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Descent of Man [ 1871]

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Bullseye
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« Reply #150 on: February 10, 2009, 01:13:24 pm »

* Audubon, Ornithological Biography, vol. i., pp. 191, 349; vol.
ii., pp. 42, 275; vol. iii., p. 2.

  Turning now to domesticated and confined birds, I will commence by
giving what little I have learnt respecting the courtship of fowls.
I have received long letters on this subject from Messrs. Hewitt and
Tegetmeier, and almost an essay from the late Mr. Brent. It will be
admitted by every one that these gentlemen, so well known from their
published works, are careful and experienced observers. They do not
believe that the females prefer certain males on account of the beauty
of their plumage; but some allowance must be made for the artificial
state under which these birds have long been kept. Mr. Tegetmeier is
convinced that a gamecock, though disfigured by being dubbed and
with his hackles trimmed, would be accepted as readily as a male
retaining all his natural ornaments. Mr. Brent, however, admits that
the beauty of the male probably aids in exciting the female; and her
acquiescence is necessary. Mr. Hewitt is convinced that the union is
by no means left to mere chance, for the female almost invariably
prefers the most vigorous, defiant, and mettlesome male; hence it is
almost useless, as he remarks, "to attempt true breeding if a
game-**** in good health and condition runs the locality, for almost
every hen on leaving the roosting-place will resort to the
game-****, even though that bird may not actually drive away the
male of her own variety." Under ordinary circumstances the males and
females of the fowl seem to come to a mutual understanding by means of
certain gestures, described to me by Mr. Brent. But hens will often
avoid the officious attentions of young males. Old hens, and hens of a
pugnacious disposition, as the same writer informs me, dislike strange
males, and will not yield until well beaten into compliance. Ferguson,
however, describes how a quarrelsome hen was subdued by the gentle
courtship of a Shanghai ****.*

  * Rare and Prize Poultry, 1854, p. 27.

  There is reason to believe that pigeons of both sexes prefer pairing
with birds of the same breed; and dovecot-pigeons dislike all the
highly improved breeds.* Mr. Harrison Weir has lately heard from a
trustworthy observer, who keeps blue pigeons, that these drive away
all other coloured varieties, such as white, red, and yellow; and from
another observer, that a female dun carrier could not, after
repeated trials, be matched with a black male, but immediately
paired with a dun. Again, Mr. Tegetmeier had a female blue turbit that
obstinately refused to pair with two males of the same breed, which
were successively shut up with her for weeks; but on being let out she
would have immediately accepted the first blue dragon that offered. As
she was a valuable bird, she was then shut up for many weeks with a
silver (i. e., very pale blue) male, and at last mated with him.
Nevertheless, as a general rule, colour appears to have little
influence on the pairing of pigeons. Mr. Tegetmeier, at my request,
stained some of his birds with magenta, but they were not much noticed
by the others.

  * Variation of Animals and Plants under Domestication, vol. ii.,
p. 103.

  Female pigeons occasionally feel a strong antipathy towards
certain males, without any assignable cause. Thus M.M. Boitard and
Corbie, whose experience extended over forty-five years, state: "Quand
une femelle eprouve de l'antipathie pour un male avec lequel on veut
l'accoupler, malgre tous les feux de l'amour, malgre l'alpiste et le
chenevis dont on la nourrit pour augmenter son ardeur malgre un
emprisonnement de six mois et meme d'un an, elle refuse constamment
ses caresses; les avances empressees, les agaceries, les tournoiemens,
les tendres roucoulemens, rien ne peut lui plaire ni l'emouvoir;
gonflee, boudeuse, blottie dans un coin de sa prison, elle n'en sort
que pour boire et manger, ou pour repousser avec une espece de rage
des caresses devenues trop pressantes."* On the other hand, Mr.
Harrison Weir has himself observed, and has heard from several
breeders, that a female pigeon will occasionally take a strong fancy
for a particular male, and will desert her own mate for him. Some
females, according to another experienced observer, Riedel,*(2) are of
a profligate disposition. and prefer almost any stranger to their
own mate. Some amorous males, called by our English fanciers "gay
birds," are so successful in their gallantries, that, as Mr. H. Weir
informs me, they must be shut up on account of the mischief which they
cause.

  * Boitard and Corbie, Les Pigeons, &c., 1824, p. 12. Prosper Lucas
(Traite de l'Hered. Nat., tom. ii., 1850, p. 296) has himself observed
nearly similar facts with pigeons.
  *(2) Die Taubenzucht, 1824, s. 86.

  Wild turkeys in the United States, according to Audubon,
"sometimes pay their addresses to the domesticated females, and are
generally received by them with great pleasure." So that these females
apparently prefer the wild to their own males.*

  * Ornithological Biography, vol. i., p. 13. See to the same
effect, Dr. Bryant, in Allen's Mammals and Birds of Florida, p. 344.

  Here is a more curious case. Sir R. Heron during many years kept
an account of the habits of the peafowl, which he bred in large
numbers. He states that "the hens have frequently great preference
to a particular peafowl. They were all so fond of an old pied ****,
that one year, when he was confined, though still in view, they were
constantly assembled close to the trellice-walls of his prison, and
would not suffer a japanned peacock to touch them. On his being let
out in the autumn, the oldest of the hens instantly courted him and
was successful in her courtship. The next year he was shut up in a
stable, and then the hens all courted his rival."* This rival was a
japanned or black-winged peacock, to our eyes a more beautiful bird
than the common kind.

  * Proceedings, Zoological Society, 1835, p. 54. The japanned peacock
is considered by Mr. Sclater as a distinct species, and has been named
Pavo nigri-pennis; but the evidence seems to me to shew that it is
only a variety.
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« Reply #151 on: February 10, 2009, 01:13:41 pm »

Lichtenstein, who was a good observer and had excellent
opportunities of observation at the Cape of Good Hope, assured
Rudolphi that the female widow-bird (Chera progne) disowns the male
when robbed of the long tail-feathers with which he is ornamented
during the breeding-season. I presume that this observation must
have been made on birds under confinement.* Here is an analogous case;
Dr. Jaeger,*(2) director of the Zoological Gardens of Vienna, states
that a male silver-pheasant, who had been triumphant over all other
males and was the accepted lover of the females, had his ornamental
plumage spoiled. He was then immediately superseded by a rival, who
got the upper hand and afterwards led the flock.

  * Rudolphi, Beitrage zur Anthropologie, 1812, s. 184.
  *(2) Die Darwin'sche Theorie, und ihre Stellung zu Moral und
Religion, 1869, s. 59.

  It is a remarkable fact, as shewing how important colour is in the
courtship of birds, that Mr. Boardman, a well-known collector and
observer of birds for many years in the Northern United States, has
never in his large experience seen an albino paired with another bird;
yet he has had opportunities of observing many albinos belonging to
several species.* It can hardly be maintained that albinos in a
state of nature are incapable of breeding, as they can be raised
with the greatest facility under confinement. It appears, therefore,
that we must attribute the fact that they do not pair to their
rejection by their normally coloured comrades.

  * This statement is given by Mr. A. Leith Adams, in his Field and
Forest Rambles, 1873, p. 76, and accords with his own experience.

  Female birds not only exert a choice, but in some few cases they
court the male, or even fight together for his possession. Sir R.
Heron states that with peafowl, the first advances are always made
by the female; something of the same kind takes place, according to
Audubon, with the older females of the wild turkey. With the
capercailzie, the females flit round the male whilst he is parading at
one of the places of assemblage, and solicit his attention.* We have
seen that a tame wild-duck seduced an unwilling pintail drake after
a long courtship. Mr. Bartlett believes that the Lophophorus, like
many other gallinaceous birds, is naturally polygamous, but two
females cannot be placed in the same cage with a male, as they fight
so much together. The following instance of rivalry is more surprising
as it relates to bullfinches, which usually pair for life. Mr.
Jenner Weir introduced a dull-coloured and ugly female into his
aviary, and she immediately attacked another mated female so
unmercifully that the latter had to be separated. The new female did
all the courtship, and was at last successful, for she paired with the
male; but after a time she met with a just retribution, for, ceasing
to be pugnacious, she was replaced by the old female, and the male
then deserted his new and returned to his old love.

  * In regard to peafowl, see Sir R. Heron, Proc. Zoolog. Soc.,
1835, p. 54, and the Rev. E. S. Dixon, Ornamental Poultry, 1848, p. 8.
For the turkey, Audubon, ibid., p. 4. For the capercailzie, Lloyd,
Game Birds of Sweden, 1867, p. 23.

  In all ordinary cases the male is so eager that he will accept any
female, and does not, as far as we can judge, prefer one to the other;
but, as we shall hereafter see, exceptions to this rule apparently
occur in some few groups. With domesticated birds, I have heard of
only one case of males shewing any preference for certain females,
namely, that of the domestic ****, who, according to the high
authority of Mr. Hewitt, prefers the younger to the older hens. On the
other hand, in effecting hybrid unions between the male pheasant and
common hens, Mr. Hewitt is convinced that the pheasant invariably
prefers the older birds. He does not appear to be in the least
influenced by their colour; but "is most capricious in his
attachments":* from some inexplicable cause he shews the most
determined aversion to certain hens, which no care on the part of
the breeder can overcome. Mr. Hewitt informs me that some hens are
quite unattractive even to the males of their own species, so that
they may be kept with several cocks during a whole season, and not one
egg out of forty or fifty will prove fertile. On the other hand,
with the long-tailed duck (Harelda glacialis), "it has been remarked,"
says M. Ekstrom, "that certain females are much more courted than
the rest. Frequently, indeed, one sees an individual surrounded by six
or eight amorous males." Whether this statement is credible, I know
not; but the native sportsmen shoot these females in order to stuff
them as decoys.*(2)

  * Mr. Hewitt, quoted in Tegetmeier's Poultry Book, 1866, p. 165.
  *(2) Quoted in Lloyd's Game Birds of Sweden, p. 345.

  With respect to female birds feeling a preference for particular
males, we must bear in mind that we can judge of choice being
exerted only by analogy. If an inhabitant of another planet were to
behold a number of young rustics at a fair courting a pretty girl, and
quarrelling about her like birds at one of their places of assemblage,
he would, by the eagerness of the wooers to please her and to
display their finery, infer that she had the power of choice. Now with
birds the evidence stands thus: they have acute powers of observation,
and they seem to have some taste for the beautiful both in colour
and sound. It is certain that the females occasionally exhibit, from
unknown causes, the strongest antipathies and preferences for
particular males. When the sexes differ in colour or in other
ornaments the males with rare exceptions are the more decorated,
either permanently or temporarily during the breeding-season. They
sedulously display their various ornaments, exert their voices, and
perform strange antics in the presence of the females. Even well-armed
males, who, it might be thought, would altogether depend for success
on the law of battle, are in most cases highly ornamented; and their
ornaments have been acquired at the expense of some loss of power.
In other cases ornaments have been acquired, at the cost of
increased risk from birds and beasts of prey. With various species
many individuals of both sexes congregate at the same spot, and
their courtship is a prolonged affair. There is even reason to suspect
that the males and females within the same district do not always
succeed in pleasing each other and pairing.
  What then are we to conclude from these facts and considerations?
Does the male parade his charms with so much pomp and rivalry for no
purpose? Are we not justified in believing that the female exerts a
choice, and that she receives the addresses of the male who pleases
her most? It is not probable that she consciously deliberates; but she
is most excited or attracted by the most beautiful, or melodious, or
gallant males. Nor need it be supposed that the female studies each
stripe or spot of colour; that the peahen, for instance, admires
each detail in the gorgeous train of the peacock- she is probably
struck only by the general effect. Nevertheless, after hearing how
carefully the male Argus pheasant displays his elegant primary
wing-feathers, and erects his ocellated plumes in the right position
for their full effect; or again, how the male goldfinch alternately
displays his gold-bespangled wings, we ought not to feel too sure that
the female does not attend to each detail of beauty. We can judge,
as already remarked, of choice being exerted, only from analogy; and
the mental powers of birds do not differ fundamentally from ours. From
these various considerations we may conclude that the pairing of birds
is not left to chance; but that those males, which are best able by
their various charms to please or excite the female, are under
ordinary circumstances accepted. If this be admitted, there is not
much difficulty in understanding how male birds have gradually
acquired their ornamental characters. All animals present individual
differences, and as man can modify his domesticated birds by selecting
the individuals which appear to him the most beautiful, so the
habitual or even occasional preference by the female of the more
attractive males would almost certainly lead to their modification;
and such modifications might in the course of time be augmented to
almost any extent, compatible with the existence of the species.
  Variability of Birds, and especially of their Secondary Sexual
Characters.- Variability and inheritance are the foundations for the
work of selection. That domesticated birds have varied greatly,
their variations being inherited, is certain. That birds in a state of
nature have been modified into distinct races is now universally
admitted.* Variations may be divided into two classes; those which
appear to our ignorance to arise spontaneously, and those which are
directly related to the surrounding conditions, so that all or
nearly all the individuals of the same species are similarly modified.
Cases of the latter kind have recently been observed with care by
Mr. J. A. Allen,*(2) who shews that in the United States many
species of birds gradually become more strongly coloured in proceeding
southward, and more lightly coloured in proceeding westward to the
arid plains of the interior. Both sexes seem generally to be
affected in a like manner, but sometimes one sex more than the
other. This result is not incompatible with the belief that the
colours of birds are mainly due to the accumulation of successive
variations through sexual selection; for even after the sexes have
been greatly differentiated, climate might produce an equal effect
on both sexes, or a greater effect on one sex than on the other, owing
to some constitutional difference.
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« Reply #152 on: February 10, 2009, 01:13:52 pm »

 * According to Dr. Blasius (Ibis, vol. ii., 1860, p. 297), there are
425 indubitable species of birds which breed in Europe, besides
sixty forms, which are frequently regarded as distinct species. Of the
latter, Blasius thinks that only ten are really doubtful, and that the
other fifty ought to be united with their nearest allies; but this
shews that there must be a considerable amount of variation with
some of our European birds. It is also an unsettled point with
naturalists, whether several North American birds ought to be ranked
as specifically distinct from the corresponding European species. So
again many North American forms which until lately were named as
distinct species, are now considered to be local races.
  *(2) Mammals and Birds of East Florida, also an Ornithological
Reconnaissance of Kansas, &c. Notwithstanding the influence of climate
on the colours birds, it is difficult to account for the dull or
dark tints of almost all the species inhabiting certain countries, for
instance, the Galapagos Islands under the equator, the wide
temperate plains of Patagonia, and, as it appears, Egypt (see Mr.
Hartshorne in the American Naturalist, 1873, p. 747). These
countries are open, and afford little shelter to birds; but it seems
doubtful whether the absence of brightly coloured species can be
explained on the principle of protection, for on the Pampas, which are
equally open, though covered by green grass, and where the birds would
be equally exposed to danger, many brilliant and conspicuously
coloured species are common. I have sometimes speculated whether the
prevailing dull tints of the scenery in the above-named countries
may not have affected the appreciation of bright colours by the
birds inhabiting them.

  Individual differences between the members of the same species are
admitted by every one to occur under a state of nature. Sudden and
strongly marked variations are rare; it is also doubtful whether if
beneficial they would often be preserved through selection and
transmitted to succeeding generations.* Nevertheless, it may be
worth while to give the few cases which I have been able to collect,
relating chiefly to colour,- simple albinism and melanism being
excluded. Mr. Gould is well known to admit the existence of few
varieties, for he esteems very slight differences as specific; yet
he states*(2) that near Bogota certain humming-birds belonging to
the genus Cynanthus are divided into two or three races or
varieties, which differ from each other in the colouring of the
tail- "some having the whole of the feathers blue, while others have
the eight central ones tipped with beautiful green." It does not
appear that intermediate gradations have been observed in this or
the following cases. In the males alone of one of the Australian
parrakeets "the thighs in some are scarlet, in others grass-green." In
another parrakeet of the same country "some individuals have the
band across the wing-coverts bright-yellow, while in others the same
part is tinged with red.*(3) In the United States some few of the
males of the scarlet tanager (Tanagra rubra) have "a beautiful
transverse band of glowing red on the smaller wing-coverts";*(4) but
this variation seems to be somewhat rare, so that its preservation
through sexual selection would follow only under usually favourable
circumstances. In Bengal the honey buzzard (Pernis cristata) has
either a small rudimental crest on its head, or none at all: so slight
a difference, however, would not have been worth notice, had not
this same species possessed in southern India a well-marked
occipital crest formed of several graduated feathers."*(5)

  * I had always perceived (Origin of Species) that rare and
strongly-marked deviations of structure, deserving to be called
monstrosities, could seldom be preserved through natural selection,
and that the preservation of even highly-beneficial variations would
depend to a certain extent on chance. I had also fully appreciated the
importance of mere individual differences, and this led me to insist
so strongly on the importance of that unconscious form of selection by
man, which follows from the preservation of the most valued
individuals of each breed, without any intention on his part to modify
the characters of the breed. But until I read an able article in the
North British Review (March 1867, p. 289, et seq.), which has been
of more use to me than any other Review, I did not see how great the
chances were against the preservation of variations, whether slight or
strongly pronounced, occurring only in single individuals.
  *(2) Introduction to the Trochlidae, p. 102.
  *(3) Gould, Handbook of Birds of Australia, vol. ii., pp. 32 and 68.
  *(4) Audubon, Ornithological Biography, 1838, vol. iv., p. 389.
  *(5) Jerdon, Birds of India, vol. i., p. 108; and Mr. Blyth, in Land
and Water, 1868, p. 381.

  The following case is in some respects more interesting. A pied
variety of the raven, with the head, breast, abdomen, and parts of the
wings and tail-feathers white, is confined to the Feroe Islands. It is
not very rare there, for Graba saw during his visit from eight to
ten living specimens. Although the characters of this variety are
not quite constant, yet it has been named by several distinguished
ornithologists as a distinct species. The fact of the pied birds being
pursued and persecuted with much clamour by the other ravens of the
island was the chief cause which led Brunnich to conclude that they
were specifically distinct; but this is now known to be an error.*
This case seems analogous to that lately given of albino birds not
pairing from being rejected by their comrades.

  * Graba, Tagebuch Reise nach Faro, 1830, ss. 51-54. Macgillivray,
History of British Birds, vol. iii., p. 745. Ibis, vol. v., 1863, p.
469.
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« Reply #153 on: February 10, 2009, 01:14:04 pm »

  In various parts of the northern seas a remarkable variety of the
common guillemot (Uria troile) is found; and in Feroe, one out of
every five birds, according to Graba's estimation, presents this
variation. It is characterised* by a pure white ring round the eye,
with a curved narrow white line, an inch and a half in length,
extending back from the ring. This conspicuous character has caused
the bird to be ranked by several ornithologists as a distinct
species under the name of U. lacrymans, but it is now known to be
merely a variety. It often pairs with the common kind, yet
intermediate gradations have never been seen; nor is this
surprising, for variations which appear suddenly, are often, as I have
elsewhere shewn,*(2) transmitted either unaltered or not at all. We
thus see that two distinct forms of the same species may co-exist in
the same district, and we cannot doubt that if the one had possessed
any advantage over the other, it would soon have been multiplied to
the exclusion of the latter. If, for instance, the male pied ravens,
instead of being persecuted by their comrades, had been highly
attractive (like the above pied peacock) to the black female ravens
their numbers would have rapidly increased. And this would have been a
case of sexual selection.

  * Graba, ibid., s. 54. Macgillivray, ibid., vol. v., p. 327.
  *(2) Variation of Animals and Plants under Domestication, vol.
ii., p. 92.

  With respect to the slight individual differences which are
common, in a greater or less degree, to all the members of the same
species, we have every reason to believe that they are by far the most
important for the work of selection. Secondary sexual characters are
eminently liable to vary, both with animals in a state of nature and
under domestication.* There is also reason to believe, as we have seen
in our eighth chapter, that variations are more apt to occur in the
male than in the female sex. All these contingencies are highly
favourable for sexual selection. Whether characters thus acquired
are transmitted to one sex or to both sexes, depends, as we shall
see in the following chapter, on the form of inheritance which
prevails.

  * On these points see also Variation of Animals and Plants under
Domestication, vol. i., p. 253; vol ii., pp. 73, 75.

  It is sometimes difficult to form an opinion whether certain
slight differences between the sexes of birds are simply the result of
variability with sexually-limited inheritance, without the aid of
sexual selection, or whether they have been augmented through this
latter process. I do not here refer to the many instances where the
male displays splendid colours or other ornaments, of which the female
partakes to a slight degree; for these are almost certainly due to
characters primarily acquired by the male having been more or less
transferred to the female. But what are we to conclude with respect to
certain birds in which, for instance, the eyes differ slightly in
colour in the two sexes?* In some cases the eyes differ conspicuously;
thus with the storks of the genus Xenorhynchus, those of the male
are blackish-hazel, whilst those of the females are gamboge-yellow;
with many hornbills (Buceros), as I hear from Mr. Blyth,*(2) the males
have intense crimson eyes, and those of the females are white. In
the Buceros bicornis, the hind margin of the casque and a stripe on
the crest of the beak are black in the male, but not so in the female.
Are we to suppose that these black marks and the crimson colour of the
eyes have been preserved or augmented through sexual selection in
the males? This is very doubtful; for Mr. Bartlett shewed me in the
Zoological Gardens that the inside of the mouth of this Buceros is
black in the male and flesh-coloured in the female; and their external
appearance or beauty would not be thus affected. I observed in
Chile*(3) that the iris in the condor, when about a year old, is
dark-brown, but changes at maturity into yellowish-brown in the
male, and into bright red in the female. The male has also a small,
longitudinal, leaden-coloured, fleshy crest or comb. The comb of
many gallinaceous birds is highly ornamental, and assumes vivid
colours during the act of courtship; but what are we to think of the
dull-coloured comb of the condor, which does not appear to us in the
least ornamental? The same question may be asked in regard to
various other characters, such as the knob on the base of the beak
of the Chinese goose (Anser cygnoides), which is much larger in the
male than in the female. No certain answer can be given to these
questions; but we ought to be cautious in assuming that knobs and
various fleshy appendages cannot be attractive to the female, when
we remember that with savage races of man various hideous deformities-
deep scars on the face with the flesh raised into protuberances, the
septum of the nose pierced by sticks or bones, holes in the ears and
lips stretched widely open- are all admired as ornamental.

  * See, for instance, on the irides of a Podica and Gallicrex in
Ibis, vol. ii., 1860, p. 206; and vol. V., 1863, p. 426.
  *(2) See also Jerdon, Birds of India, vol. i., pp. 243-245
  *(3) Zoology of the Voyage of H. M. S. Beagle, 1841, p. 6.

  Whether or not unimportant differences between the sexes, such as
those just specified, have been preserved through sexual selection,
these differences, as well as all others, must primarily depend on the
laws of variation. On the principle of correlated development, the
plumage often varies on different parts of the body, or over the whole
body, in the same manner. We see this well illustrated in certain
breeds of the fowl. In all the breeds the feathers on the neck and
loins of the males are elongated, and are called hackles; now when
both sexes acquire a top-knot, which is a new character in the
genus, the feathers on the head of the male become hackle-shaped,
evidently on the principle of correlation; whilst those on the head of
the female are of the ordinary shape. The colour also of the hackles
forming the top-knot of the male, is often correlated with that of the
hackles on the neck and loins, as may be seen by comparing these
feathers in the golden and silver-spangled Polish, the Houdans, and
Creve-coeur breeds. In some natural species we may observe exactly the
same correlation in the colours of these same feathers, as in the
males of the splendid gold and Amherst pheasants.
  The structure of each individual feather, generally causes any
change in its colouring to be symmetrical; we see this in the
various laced, spangled, and pencilled breeds of the fowl; and on
the principle of correlation the feathers over the whole body are
often coloured in the same manner. We are thus enabled without much
trouble to rear breeds with their plumage marked almost as
symmetrically as in natural species. In laced and spangled fowls the
coloured margins of the feathers are abruptly defined; but in a
mongrel raised by me from a black Spanish **** glossed with green, and
a white game-hen, all the feathers were greenish-black, excepting
towards their extremities, which were yellowish-white; but between the
white extremities and the black bases, there was on each feather a
symmetrical, curved zone of dark-brown. In some instances the shaft ofthe feather determines the distribution of the tints; thus with the
body-feathers of a mongrel from the same black Spanish **** and a
silver-spangled Polish hen, the shaft, together with a narrow space on
each side, was greenish-black, and this was surrounded by a regular
zone of dark-brown, edged with brownish-white. In these cases we
have feathers symmetrically shaded, like those which give so much
elegance to the plumage of many natural species. I have also noticed a
variety of the common pigeon with the wing-bars symmetrically zoned
with three bright shades, instead of being simply black on a
slaty-blue ground, as in the parent-species.
  In many groups of birds the plumage is differently coloured in the
several species, yet certain spots, marks, or stripes are retained
by all. Analogous cases occur with the breeds of the pigeon, which
usually retain the two wing-bars, though they may be coloured red,
yellow, white, black, or blue, the rest of the plumage being of some
wholly different tint. Here is a more curious case, in which certain
marks are retained, though coloured in a manner almost exactly the
opposite of what is natural; the aboriginal pigeon has a blue tail,
with the terminal halves of the outer webs of the two outer tail
feathers white; now there is a sub-variety having a white instead of a
blue tail, with precisely that part black which is white in the
parent-species.*
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« Reply #154 on: February 10, 2009, 01:14:18 pm »

* Bechstein, Naturgeschichte Deutschlands, B. iv., 1795, s. 31, on a
sub-variety of the monck pigeon.

  Formation and Variability of the Ocelli or eye-like Spots on the
Plumage of Birds.- As no ornaments are more beautiful than the
ocelli on the feathers of various birds, on the hairy coats of some
mammals, on the scales of reptiles and fishes, on the skin of
amphibians, on the wings of many Lepidoptera and other insects, they
deserve to be especially noticed. An ocellus consists of a spot within
a ring of another colour, like the pupil within the iris, but the
central spot is often surrounded by additional concentric zones. The
ocelli on the tail-coverts of the peacock offer a familiar example, as
well as those on the wings of the peacock-butterfly (Vanessa). Mr.
Trimen has given me a description of a S. African moth (Gynanisa
isis), allied to our emperor moth, in which a magnificent ocellus
occupies nearly the whole surface of each hinder wing; it consists
of a black centre, including a semi-transparent crescent-shaped
mark, surrounded by successive, ochre-yellow, black, ochre-yellow,
pink, white, pink, brown, and whitish zones. Although we do not know
the steps by which these wonderfully beautiful and complex ornaments
have been developed, the process has probably been a simple one, at
least with insects; for, as Mr. Trimen writes to me, "no characters of
mere marking or colouration are so unstable in the Lepidoptera as
the ocelli, both in number and size." Mr. Wallace, who first called my
attention to this subject, shewed me a series of specimens of our
common meadow-brown butterfly (Hipparchia janira) exhibiting
numerous gradations from a simple minute black spot to an
elegantly-shaded ocellus. In a S. African butterfly (Cyllo leda,
Linn.), belonging to the same family, the ocelli are even still more
variable. In some specimens (see A, fig. 53) large spaces on the upper
surface of the wings are coloured black, and include irregular white
marks; and from this state a complete gradation can be traced into a
tolerably perfect ocellus (A1), and this results from the
contraction of the irregular blotches of colour. In another series
of specimens a gradation can be followed from excessively minute white
dots, surrounded by a scarcely visible black line (B), into
perfectly symmetrical and large ocelli (B1).* In cases like these, the
development of a perfect ocellus does not require a long course of
variation and selection.

  * This woodcut has been engraved from a beautiful drawing, most
kindly made for me by Mr. Trimen; see also his description of the
wonderful amount of variation in the coloration and shape of the wings
this butterfly, in his Rhopalocera Africae, Australis, p. 186.

  With birds and many other animals, it seems to follow from the
comparison of allied species that circular spots are often generated
by the breaking up and contraction of stripes. In the tragopan
pheasant faint white lines in the female represent the beautiful white
spots in the male;* and something of the same kind may be observed
in the two sexes of the Argus pheasant. However this may be,
appearances strongly favour the belief that on the one hand, a dark
spot is often formed by the colouring matter being drawn towards a
central point from a surrounding zone, which latter is thus rendered
lighter; and, on the other hand, that a white spot is often formed
by the colour being driven away from a central point, so that it
accumulates in a surrounding darker zone. In either case an ocellus is
the result. The colouring matter seems to be a nearly constant
quantity, but is redistributed, either centripetally or centrifugally.
The feathers of the common guinea-fowl offer a good instance of
white spots surrounded by darker zones; and wherever the white spots
are large and stand near each other, the surrounding dark zones become
confluent. In the same wing-feather of the Argus pheasant dark spots
may be seen surrounded by a pale zone, and white spots by a dark zone.
Thus the formation of an ocellus in its most elementary state
appears to be a simple affair. By what further steps the more
complex ocelli, which are surrounded by many successive zones Of
colour, have been generated, I will not pretend to say. But the
zoned feathers of the mongrels from differently coloured fowls, and
the extraordinary variability of the ocelli on many Lepidoptera,
lead us to conclude that their formation is not a complex process, but
depends on some slight and graduated change in the nature of the
adjoining tissues.

  * Jerdon, Birds of India, vol. iii., p. 517.

  Gradation of Secondary Sexual Characters.- Cases of gradation are
important, as shewing us that highly complex ornaments may be acquired
by small successive steps. In order to discover the actual steps by
which the male of any existing bird has acquired his magnificent
colours or other ornaments, we ought to behold the long line of his
extinct progenitors; but this is obviously impossible. We may,
however, generally gain a clue by comparing all the species of the
same group, if it be a large one; for some of them will probably
retain, at least partially, traces of their former characters. Instead
of entering on tedious details respecting various groups, in which
striking instances of gradation could be given, it seems the best plan
to take one or two strongly marked cases, for instance that of the
peacock, in order to see if light can be thrown on the steps by
which this bird bas become so splendidly decorated. The peacock is
chiefly remarkable from the extraordinary length of his
tail-coverts; the tail itself not being much elongated. The barbs
along nearly the whole length of these feathers stand separate or
are decomposed; but this is the case with the feathers of many
species, and with some varieties of the domestic fowl and pigeon.
The barbs coalesce towards the extremity of the shaft forming the oval
disc or ocellus, which is certainly one of the most beautiful
objects in the world. It consists of an iridescent, intensely blue,
indented centre, surrounded by a rich green zone, this by a broad
coppery-brown zone, and this by five other narrow zones of slightly
different iridescent shades. A trifling character in the disc deserves
notice; the barbs, for a space along one of the concentric zones are
more or less destitute of their barbules, so that a part of the disc
is surrounded by an almost transparent zone, which gives it a highly
finished aspect. But I have elsewhere described* an exactly
analogous variation in the hackles of a sub-variety of the
game-****, in which the tips, having a metallic lustre, "are separated
from the lower part of the feather by a symmetrically shaped
transparent zone, composed of the naked portions of the barbs." The
lower margin or base of the dark-blue centre of the ocellus is
deeply indented on the line of the shaft. The surrounding zones
likewise shew traces, as may be seen in the drawing (see fig. 54),
of indentations, or rather breaks. These indentations are common to
the Indian and Javan peacocks (Pavo cristatus and P. muticus); and
they seem to deserve particular attention, as probably connected
with the development of the ocellus; but for a long time I could not
conjecture their meaning.

  * Variation of Animals and Plants under Domestication, vol. i., p.
254.
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« Reply #155 on: February 10, 2009, 01:14:31 pm »

If we admit the principle of gradual evolution, there must
formerly have existed many species which presented every successive
step between the wonderfully elongated tail-coverts of the peacock and
the short tail-coverts of all ordinary birds; and again between the
magnificent ocelli of the former, and the simpler ocelli or mere
coloured spots on other birds; and so with all the other characters of
the peacock. Let us look to the allied Gallinaceae for any
still-existing gradations. The species and sub-species of Polyplectron
inhabit countries adjacent to the native land of the peacock; and they
so far resemble this bird that they are sometimes called
peacock-pheasants. I am also informed by Mr. Bartlett that they
resemble the peacock in their voice and in some of their habits.
During the spring the males, as previously described, strut about
before the comparatively plain-coloured females, expanding and
erecting their tail and wing-feathers, which are ornamented with
numerous ocelli. I request the reader to turn back to the drawing (see
fig. 51) of a Polyplectron; In P. napoleonis the ocelli are confined
to the tail, and the back is of a rich metallic blue; in which
respects this species approaches the Java peacock P. hardwickii
possesses a peculiar topknot, which is also somewhat like that of
the Java peacock. In all species the ocelli on the wings and tail
are either circular or oval, and consist of a beautiful, iridescent,
greenish-blue or greenish-purple disc, with a black border. This
border in P. chinquis shades into brown. edged with cream colour, so
that the ocellus is here surrounded with variously shaded, though
not bright, concentric zones. The unusual length of the tail-coverts
is another remarkable character in Polyplectron; for in some of the
species they are half, and in others two-thirds as long as the true
tail-feathers. The tail-coverts are ocellated as in the peacock.
Thus the several species of Polyplectron manifestly make a graduated
approach to the peacock in the length of their tail-coverts, in the
zoning of the ocelli, and in some other characters.
  Notwithstanding this approach, the first species of Polyplectron
which I examined almost made me give up the search; for I found not
only that the true tail-feathers, which in the peacock are quite
plain, were ornamented with ocelli, but that the ocelli on all the
feathers differed fundamentally from those of the peacock, in there
being two on the same feather (see fig. 55), one on each side of the
shaft.
  Hence I concluded that the early progenitors of the peacock could
not have resembled a Polyplectron. But on continuing my search, I
observed that in some of the species the two ocelli stood very near
each other; that in the tail-feathers of P. hardwickii they touched
each other; and, finally, that on the tail-coverts of this same
species as well as of P. malaccense (see fig. 56) they were actually
confluent. As the central part alone is confluent, an indentation is
left at both the upper and lower ends; and the surrounding coloured
zones are likewise indented. A single ocellus is thus formed on each
tail-covert, though still plainly betraying its double origin. These
confluent ocelli differ from the single ocelli of the peacock in
having an indentation at both ends, instead of only at the lower or
basal end. The explanation, however, of this difference is not
difficult; in some species of Polyplectron the two oval ocelli on
the same feather stand parallel to each other; in other species (as in
P. chinquis) they converge towards one end; now the partial confluence
of two convergent ocelli would manifestly leave a much deeper
indentation at the divergent than at the convergent end. It is also
manifest that if the convergence were strongly pronounced and the
confluence complete, the indentation at the convergent end would
tend to disappear.
  The tail-feathers in both species of the peacock are entirely
destitute of ocelli, and this apparently is related to their being
covered up and concealed by the long tail-coverts. In this respect
they differ remarkably from the tail-feathers of Polyplectron, which
in most of the species are ornamented with larger ocelli than those on
the tail-coverts. Hence I was led carefully to examine the
tail-feathers of the several species, in order to discover whether
their ocelli shewed any tendency to disappear; and to my great
satisfaction, this appeared to be so. The central tail-feathers of
P. napoleonis have the two ocelli on each side of the shaft
perfectly developed; but the inner ocellus becomes less and less
conspicuous on the more exterior tail-feathers, until a mere shadow or
rudiment is left on the inner side of the outermost feather. Again, in
P. malaccense, the ocelli on the tail-coverts are, as we have seen,
confluent; and these feathers are of unusual length, being
two-thirds of the length of the tail-feathers, so that in both these
respects they approach the tail-coverts of the peacock. Now in P.
malaccense, the two central tail-feathers alone are ornamented, each
with two brightly-coloured ocelli, the inner ocellus having completely
disappeared from all the other tail-feathers. Consequently the
tail-coverts and tail-feathers of this species of Polyplectron make
a near approach in structure and ornamentation to the corresponding
feathers of the peacock.
  As far, then, as gradation throws light on the steps by which the
magnificent train of the peacock has been acquired, hardly anything
more is needed. If we picture to ourselves a progenitor of the peacock
in an almost exactly intermediate condition between the existing
peacock, with his enormously elongated tail-coverts, ornamented with
single ocelli, and an ordinary gallinaceous bird with short
tail-coverts, merely spotted with some colour, we shall see a bird
allied to Polyplectron- that is, with tail-coverts, capable of
**** and expansion, ornamented with two partially confluent
ocelli, and long enough almost to conceal the tail-feathers, the
latter having already partially lost their ocelli. The indentation
of the central disc and of the surrounding zones of the ocellus, in
both species of peacock, speaks plainly in favour of this view, and is
otherwise inexplicable. The males of Polyplectron are no doubt
beautiful birds, but their beauty, when viewed from a little distance,
cannot be compared with that of the peacock. Many female progenitors
of the peacock must, during a long line of descent, have appreciated
this superiority; for they have unconsciously, by the continued
preference for the most beautiful males, rendered the peacock the most
splendid of living birds.
  Argus pheasant.- Another excellent case for investigation is offered
by the ocelli on the wing-feathers of the Argus pheasant, which are
shaded in so wonderful a manner as to resemble balls lying loose
within sockets, and consequently differ from ordinary ocelli. No
one, I presume, will attribute the shading, which has excited the
admiration of many experienced artists, to chance- to the fortuitous
concourse of atoms of colouring matter. That these ornaments should
have been formed through the selection of many successive
variations, not one of which was originally intended to produce the
ball-and-socket effect, seems as incredible as that one of Raphael's
Madonnas should have been formed by the selection of chance daubs of
paint made by a long succession of young artists, not one of whom
intended at first to draw the human figure. In order to discover how
the ocelli have been developed, we cannot look to a long line of
progenitors, nor to many closely-allied forms, for such do not now
exist. But fortunately the several feathers on the wing suffice to
give us a clue to the problem, and they prove to demonstration that
a gradation is at least possible from a mere spot to a finished
ball-and-socket ocellus.
  The wing-feathers, bearing the ocelli, are covered with dark stripes
(see fig. 57) or with rows of dark spots (see fig. 59), each stripe or
row of spots running obliquely down the outer side of the shaft to one
of the ocelli. The spots are generally elongated in a line
transverse to the row in which they stand. They often become confluent
either in the line of the row- and then they form a longitudinal
stripe- or transversely, that is, with the spots in the adjoining
rows, and then they form transverse stripes. A spot sometimes breaks
up into smaller spots, which still stand in their proper places.
  It will be convenient first to describe a perfect ball-and-socket
ocellus. This consists of an intensely black circular ring,
surrounding a space shaded so as exactly to resemble a ball. The
figure here given has been admirably drawn by Mr. Ford and well
engraved, but a woodcut cannot exhibit the exquisite shading of the
original. The ring is almost always slightly broken or interrupted
(see fig. 57) at a point in the upper half, a little to the right of
and above the white shade on the enclosed ball; it is also sometimes
broken towards the base on the right hand. These little breaks have an
important meaning. The ring is always much thickened, with the edges
ill-defined towards the left-hand upper corner, the feather being beld
erect, in the position in which it is here drawn. Beneath this
thickened part there is on the surface of the ball an oblique almost
pure-white mark, which shades off downwards into a pale-leaden hue,
and this into yellowish and brown tints, which insensibly become
darker and darker towards the lower part of the ball. It is this
shading which gives so admirably the effect of light shining on a
convex surface. If one of the balls be examined, it will be seen
that the lower part is of a brown tint and is indistinctly separated
by a curved oblique line from the upper part which is yellower and
more leaden; this curved oblique line runs at right angles to the
longer axis of the white patch of light, and indeed of all the
shading; but this difference in colour, which cannot of course be
shewn in the woodcut, does not in the least interfere with the perfect
shading of the ball. It should be particularly observed that each
ocellus stands in obvious connection either with a dark stripe, or
with a longitudinal row of dark spots for both occur indifferently
on the same feather. Thus in fig. 57 (see figure) stripe A runs to
ocellus (a); B runs to ocellus (b); stripe C is broken in the upper
part, and runs down to the next succeeding ocellus, not represented in
the woodcut; D to the next lower one, and so with the stripes E and F.
Lastly, the several ocelli are separated from each other by a pale
surface bearing irregular black marks.
  I will next describe the other extreme of the series, namely, the
first trace of an ocellus. The short secondary wing-feather (see
fig. 58), nearest to the body, is marked like the other feathers, with
oblique, longitudinal, rather irregular, rows of very dark spots.
The basal spot, or that nearest the shaft, in the five lower rows
(excluding the lowest one) is a little larger than the other spots
of the same row, and a little more elongated in a transverse
direction. It differs also from the other spots by being bordered on
its upper side with some dull fulvous shading. But this spot is not in
any way more remarkable than those on the plumage of many birds, and
might easily be overlooked. The next higher spot does not differ atall from the upper ones in the same row. The larger basal spots occupy
exactly the same relative position on these feathers as do the perfect
ocelli on the longer wing-feathers.
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« Reply #156 on: February 10, 2009, 01:14:46 pm »

By looking to the next two or three succeeding wing-feathers, an
absolutely insensible gradation can be traced from one of the last
described basal spots, together with the next higher one in the same
row, to a curious ornament, which cannot be called an ocellus, and
which I will name, from the want of a better term, an "elliptic
ornament." These are shewn in the accompanying figure (see fig. 59).
We here see several oblique rows, A, B, C, D, &c. (see the lettered
diagram on the right hand), of dark spots of the usual character. Each
row of spots runs down to and is connected with one of the elliptic
ornaments, in exactly the same manner as each stripe in fig. 57 (see
figure) runs down to, and is connected with, one of the
ball-and-socket ocelli. Looking to any one row, for instance, B, in
fig. 59 (see figure), the lowest mark (b) is thicker and
considerably longer than the upper spots, and has its left extremity
pointed and curved upwards. This black mark is abruptly bordered on
its upper side by a rather broad space of richly shaded tints,
beginning with a narrow brown zone, which passes into orange, and this
into a pale leaden tint, with the end towards the shaft much paler.
These shaded tints together fill up the whole inner space of the
elliptic ornament. The mark (b) corresponds in every respect with
the basal shaded spot of the simple feather described in the last
paragraph (see fig. 58), but is more highly developed and more
brightly coloured. Above and to the right of this spot (see b, fig.
59), with its bright shading, there is a long narrow, black mark
(c), belonging to the same row, and which is arched a little downwards
so as to face (b). This mark is sometimes broken into two portions. It
is also narrowly edged on the lower side with a fulvous tint. To the
left of and above (c), in the same oblique direction, but always
more or less distinct from it, there is another black mark (d). This
mark is generally sub-triangular and irregular in shape, but in the
one lettered in the diagram it is unusually narrow, elongated, and
regular. It apparently consists of a lateral and broken prolongation
of the mark (c), together with its confluence with a broken and
prolonged part of the next spot above; but I do not feel sure of this.
These three marks, b, c, and d, with the intervening bright shades,
form together the so-called elliptic ornament. These ornaments
placed parallel to the shaft, manifestly correspond in position with
the ball-and-socket ocelli. Their extremely elegant appearance
cannot be appreciated in the drawing, as the orange and leaden
tints, contrasting so well with the black marks, cannot be shewn.
  Between one of the elliptic ornaments and a perfect
ball-and-socket ocellus, the gradation is so perfect that it is
scarcely possible to decide when the latter term ought to be used. The
passage from the one into the other is effected by the elongation
and greater curvature in opposite directions of the lower black mark
(see b, fig. 59), and more especially of the upper one (c), together
with the contraction of the elongated sub-triangular or narrow mark
(d), so that at last these three marks become confluent, forming an
irregular elliptic ring. This ring is gradually rendered more and more
circular and regular, increasing at the same time in diameter. I
have here given a drawing (see fig. 60) of the natural size of an
ocellus not as yet quite perfect. The lower part of the black ring
is much more curved than is the lower mark in the elliptic ornament
(see b, fig. 59). The upper part of the ring consists of two or
three separate portions; and there is only a trace of the thickening
of the portion which forms the black mark above the white shade.
This white shade itself is not as yet much concentrated; and beneath
it the surface is brighter coloured than in a perfect
ball-and-socket ocellus. Even in the most perfect ocelli traces of the
junction of three or four elongated black marks, by which the ring has
been formed, may often be detected. The irregular sub-triangular or
narrow mark (see d, fig. 59), manifestly forms, by its contraction and
equalisation, the thickened portion of the ring above the white
shade on a perfect ball-and-socket ocellus. The lower part of the ring
is invariably a little thicker than the other parts (see fig. 57), and
this follows from the lower black mark of the elliptic ornament (see
b, fig. 59) having originally been thicker than the upper mark (c).
Every step can be followed in the process of confluence and
modification; and the black ring which surrounds the ball of the
ocellus is unquestionably formed by the union and modification of
the three black marks, b, c, d, of the elliptic ornament. The
irregular zigzag black marks between the successive ocelli (see
again fig. 57) are plainly due to the breaking up of the somewhat more
regular but similar marks between the elliptic ornaments.
  The successive steps in the shading of the ball-and-socket ocelli
can be followed out with equal clearness. The brown, orange, and
pale-leadened narrow zones, which border the lower black mark of the
elliptic ornament, can be seen gradually to become more and more
softened and shaded into each other, with the upper lighter part
towards the left-hand corner rendered still lighter, so as to become
almost white, and at the same time more contracted. But even in the
most perfect ball-and-socket ocelli a slight difference in the
tints, though not in the shading, between the upper and lower parts of
the ball can be perceived, as before noticed; and the line of
separation is oblique, in the same direction as the bright coloured
shades of the elliptic ornaments. Thus almost every minute detail in
the shape and colouring of the ball-and-socket ocelli can be shewn
to follow from gradual changes in the elliptic ornaments; and the
development of the latter can be traced by equally small steps from
the union of two almost simple spots, the lower one (see fig. 58)
having some dull fulvous shading on its upper side.
  The extremities of the longer secondary feathers which bear the
perfect ball-and-socket ocelli, are peculiarly ornamented (see fig.
61). The oblique longitudinal stripes suddenly cease upwards and
become confused; and above this limit the whole upper end of the
feather (a) is covered with white dots, surrounded by little black
rings, standing on a dark ground. The oblique stripe belonging to
the uppermost ocellus (b) is barely represented by a very short
irregular black mark with the usual, curved, transverse base. As
this stripe is thus abruptly cut off, we can perhaps understand from
what has gone before, how it is that the upper thickened part of the
ring is here absent; for, as before stated, this thickened part
apparently stands in some relation with a broken prolongation from the
next higher spot. From the absence of the upper and thickened part
of the ring, the uppermost ocellus, though perfect in all other
respects, appears as if its top had been obliquely sliced off. It
would, I think, perplex any one, who believes that the plumage of
the Argus pheasant was created as we now see it, to account for the
imperfect condition of the uppermost ocellus. I should add that on the
secondary wing-feather farthest from the body all the ocelli are
smaller and less perfect than on the other feathers, and have the
upper part of the ring deficient, as in the case just mentioned. The
imperfection here seems to be connected with the fact that the spots
on this feather shew less tendency than usual to become confluent into
stripes; they are, on the contrary, often broken up into smaller
spots, so that two or three rows run down to the same ocellus.
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« Reply #157 on: February 10, 2009, 01:15:00 pm »

There still remains another very curious point, first observed by
Mr. T. W. Wood,* which deserves attention. In a photograph, given me
by Mr. Ward, of a specimen mounted as in the act of display, it may be
seen that on the feathers which are held perpendicularly, the white
marks on the ocelli, representing light reflected from a convex
surface, are at the upper or further end, that is, are directed
upwards; and the bird whilst displaying himself on the ground would
naturally be illuminated from above. But here comes the curious point;
the outer feathers are held almost horizontally, and their ocelli
ought likewise to appear as if illuminated from above, and
consequently the white marks ought to be placed on the upper sides
of the ocelli; and, wonderful as is the fact, they are thus placed!
Hence the ocelli on the several feathers, though occupying very
different positions with respect to the light, all appear as if
illuminated from above, just as an artist would have shaded them.
Nevertheless they are not illuminated from strictly the same point
as they ought to be; for the white marks on the ocelli of the feathers
which are held almost horizontally, are placed rather too much towards
the further end; that is, they are not sufficiently lateral. We
have, however, no right to expect absolute perfection in a part
rendered ornamental through sexual selection, any more than we have in
a part modified through natural selection for real use; for
instance, in that wondrous organ the human eye. And we know what
Helmholtz, the highest authority in Europe on the subject, has said
about the human eye; that if an optician had sold him an instrument so
carelessly made, he would have thought himself fully justified in
returning it.*(2)

  * The Field, May 28, 1870.
  *(2) Popular Lectures on Scientific Subjects, Eng. trans., 1873, pp.
219, 227, 269, 390.

  We have now seen that a perfect series can be followed, from
simple spots to the wonderful ball-and-socket ornaments. Mr. Gould,
who kindly gave me some of these feathers, fully agrees with me in the
completeness of the gradation. It is obvious that the stages in
development exhibited by the feathers on the same bird do not at all
necessarily shew us the steps passed through by the extinct
progenitors of the species; but they probably give us the clue to
the actual steps, and they at least prove to demonstration that a
gradation is possible. Bearing in mind how carefully the male Argus
pheasant displays his plumes before the female, as well as the many
facts rendering it probable that female birds prefer the more
attractive males, no one who admits the agency of sexual selection
in any case will deny that a simple dark spot with some fulvous
shading might be converted, through the approximation and modification
of two adjoining spots, together with some slight increase of
colour, into one of the so-called elliptic ornaments. These latter
ornaments have been shewn to many persons, and all have admitted
that they are beautiful, some thinking them even more so than the
ball-and-socket ocelli. As the secondary plumes became lengthened
through sexual selection, and as the elliptic ornaments increased in
diameter, their colours apparently became less bright; and then the
ornamentation of the plumes had to be gained by an improvement in
the pattern and shading; and this process was carried on until the
wonderful ball-and-socket ocelli were finally developed. Thus we can
understand- and in no other way as it seems to me- the present
condition and origin of the ornaments on the wing-feathers of the
Argus pheasant.

  From the light afforded by the principle of gradation- from what
we know of the laws of variation- from the changes which have taken
place in many of our domesticated birds- and, lastly, from the
character (as we shall hereafter see more clearly) of the immature
plumage of young birds- we can sometimes indicate, with a certain
amount of confidence, the probable steps by which the males have
acquired their brilliant plumage and various ornaments; yet in many
cases we are involved in complete darkness. Mr. Gould several years
ago pointed out to me a humming-bird, the Urosticte benjamini,
remarkable for the curious differences between the sexes. The male,
besides a splendid gorget, has greenish-black tail-feathers, with
the four central ones tipped with white; in the female, as with most
of the allied species, the three outer tail-feathers on each side
are tipped with white, so that the male has the four central, whilst
the female has the six exterior feathers ornamented with white tips.
What makes the case more curious is that, although the colouring of
the tail differs remarkably in both sexes of many kinds of
humming-birds, Mr. Gould does not know a single species, besides the
Urosticte, in which the male has the four central feathers tipped with
white.
  The Duke of Argyll, in commenting on this case,* passes over
sexual selection, and asks, "What explanation does the law of
natural selection give of such specific varieties as these?" He
answers "none whatever"; and I quite agree with him. But can this be
so confidently said of sexual selection? Seeing in how many ways the
tail-feathers of humming-birds differ, why should not the four central
feathers have varied in this one species alone, so as to have acquired
white tips? The variations may have been gradual, or somewhat abrupt
as in the case recently given of the humming-birds near Bogota, in
which certain individuals alone have the "central tail-feathers tipped
with beautiful green." In the female of the Urosticte I noticed
extremely minute or rudimental white tips to the two outer of the four
central black tail-feathers; so that here we have an indication of
change of some kind in the plumage of this species. If we grant the
possibility of the central tail-feathers of the male varying in
whiteness, there is nothing strange in such variations having been
sexually selected. The white tips, together with the small white
ear-tufts, certainly add, as the Duke of Argyll admits, to the
beauty of the male; and whiteness is apparently appreciated by other
birds, as may be inferred from such cases as the snow-white male of
the bell-bird. The statement made by Sir R. Heron should not be
forgotten, namely, that his peahens, when debarred from access to
the pied peacock, would not unite with any other male, and during that
season produced no offspring. Nor is it strange that variations in the
tail-feathers of the Urosticte should have been specially selected for
the sake of ornament, for the next succeeding genus in the family
takes its name of Metallura from the splendour of these feathers. We
have, moreover, good evidence that humming-birds take especial pains
in displaying their tail-feathers; Mr. Belt,*(2) after describing
the beauty of the Florisuga mellivora, says, "I have seen the female
sitting on a branch, and two males displaying their charms in front of
her. One would shoot up like a rocket, then suddenly expanding the
snow-white tail, like an inverted parachute, slowly descend in front
of her, turning round gradually to shew off back and front.... The
expanded white tail covered more space than all the rest of the
bird, and was evidently the grand feature in the performance. Whilst
one male was descending, the other would shoot up and come slowly down
expanded. The entertainment would end in a fight between the two
performers; but whether the most beautiful or the most pugnacious
was the accepted suitor, I know not." Mr. Gould, after describing
the peculiar plumage of the Urosticte, adds, "that ornament and
variety is the sole object, I have myself but little doubt."*(3) If
this be admitted, we can perceive that the males which during former
times were decked in the most elegant and novel manner would have
gained an advantage, not in the ordinary struggle for life, but in
rivalry with other males, and would have left a larger number of
offspring to inherit their newly-acquired beauty.

  * The Reign of Law, 1867, p. 247.
  *(2) The Naturalist in Nicaragua, 1874, p. 112.
  *(3) Introduction to the Trochilidae, 1861, p. 110.



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« Reply #158 on: February 10, 2009, 01:15:22 pm »

Chapter XV - Birds- Continued

  WE have in this chapter to consider why the females of many birds
have not acquired the same ornaments as the male; and why, on the
other hand, both sexes of many other birds are equally, or almost
equally, ornamented? In the following chapter we shall consider the
few cases in which the female is more conspicuously coloured than
the male.
  In my Origin of Species* I briefly suggested that the long tail of
the peacock would be inconvenient and the conspicuous black colour
of the male capercailzie dangerous, to the female during the period of
incubation: and consequently that the transmission of these characters
from the male to the female offspring had been checked through natural
selection. I still think that this may have occurred in some few
instances: but after mature reflection on all the facts which I have
been able to collect, I am now inclined to believe that when the sexes
differ, the successive variations have generally been from the first
limited in their transmission to the same sex in which they first
arose. Since my remarks appeared, the subject of sexual colouration
has been discussed in some very interesting papers by Mr. Wallace,*(2)
who believes that in almost all cases the successive variations tended
at first to be transmitted equally to both sexes; but that the
female was saved, through natural selection, from acquiring the
conspicuous colours of the male, owing to the danger which she would
thus have incurred during incubation.

  * Fourth edition, 1866, p. 241.
  *(2) Westminster Review, July, 1867. Journal of Travel, vol. i.,
1868, p. 73.

  This view necessitates a tedious discussion on a difficult point,
namely, whether the transmission of a character, which is at first
inherited by both sexes can be subsequently limited in its
transmission to one sex alone by means of natural selection. We must
bear in mind, as shewn in the preliminary chapter on sexual selection,
that characters which are limited in their development to one sex
are always latent in the other. An imaginary illustration will best
aid us in seeing the difficulty of the case; we may suppose that a
fancier wished to make a breed of pigeons, in which the males alone
should be coloured of a pale blue, whilst the females retained their
former slaty tint. As with pigeons characters of all kinds are usually
transmitted to both sexes equally, the fancier would have to try to
convert this latter form of inheritance into sexually-limited
transmission. All that he could do would be to persevere in
selecting every male pigeon which was in the least degree of a paler
blue; and the natural result of this process, if steadily carried on
for a long time, and if the pale variations were strongly inherited or
often recurred, would be to make his whole stock of a lighter blue.
But our fancier would be compelled to match, generation after
generation, his pale blue males with slaty females, for he wishes to
keep the latter of this colour. The result would generally be the
production either of a mongrel piebald lot, or more probably the
speedy and complete loss of the pale-blue tint; for the primordial
slaty colour would be transmitted with prepotent force. Supposing,
however, that some pale-blue males and slaty females were produced
during each successive generation, and were always crossed together,
then the slaty females would have, if I may use the expression, much
blue blood in their veins, for their fathers, grandfathers, &c.,
will all have been blue birds. Under these circumstances it is
conceivable (though I know of no distinct facts rendering it probable)
that the slaty females might acquire so strong a latent tendency to
pale-blueness, that they would not destroy this colour in their male
offspring, their female offspring still inheriting the slaty tint.
If so, the desired end of making a breed with the two sexes
permanently different in colour might be gained.
  The extreme importance, or rather necessity in the above case of the
desired character, namely, pale-blueness, being present though in a
latent state in the female, so that the male offspring should not be
deteriorated, will be best appreciated as follows: the male of
Soemmerring's pheasant has a tail thirty-seven inches in length,
whilst that of the female is only eight inches; the tail of the male
common pheasant is about twenty inches, and that of the female
twelve inches long. Now if the female Soemmerring pheasant with her
short tail were crossed with the male common pheasant, there can be no
doubt that the male hybrid offspring would have a much longer tail
than that of the pure offspring of the common pheasant. On the other
hand, if the female common pheasant, with a tail much longer than that
of the female Soemmerring pheasant, were crossed with the male of
the latter, the male hybrid offspring would have a much shorter tail
than that of the pure offspring of Soemmerring's pheasant.*

  * Temminck says that the tail of the female Phasianus
Soemmerringii is only six inches long, Planches coloriees, vol. v.,
1838, pp. 487 and 488: the measurements above given were made for me
by Mr. Sclater. For the common pheasant, see Macgillivray, History
of British Birds, vol. i., pp. 118-121.

  Our fancier, in order to make his new breed with the males of a
pale-blue tint, and the females unchanged, would have to continue
selecting the males during many generations; and each stage of
paleness would have to be fixed in the males, and rendered latent in
the females. The task would be an extremely difficult one, and has
never been tried, but might possibly be successfully carried out.
The chief obstacle would be the early and complete loss of the
pale-blue tint, from the necessity of reiterated crosses with the
slaty female, the latter not having at first any latent tendency to
produce pale-blue offspring.
  On the other hand, if one or two males were to vary ever so slightly
in paleness, and the variations were from the first limited in their
transmission to the male sex, the task of making a new breed of the
desired kind would be easy, for such males would simply have to be
selected and matched with ordinary females. An analogous case has
actually occurred, for there are breeds of the pigeon in Belgium* in
which the males alone are marked with black striae. So again Mr.
Tegetmeier has recently shewn*(2) that dragons not rarely produce
silver-coloured birds, which are almost always hens; and he himself
has bred ten such females. It is on the other hand a very unusual
event when a silver male is produced; so that nothing would be easier,
if desired, than to make a breed of dragons with blue males and silver
females. This tendency is indeed so strong that when Mr. Tegetmeier at
last got a silver male and matched him with one of the silver females,
he expected to get a breed with both sexes thus coloured; he was
however disappointed, for the young male reverted to the blue colour
of his grandfather, the young female alone being silver. No doubt with
patience this tendency to reversion in the males, reared from an
occasional silver male matched with a silver hen, might be eliminated,
and then both sexes would be coloured alike; and this very process has
been followed with success by Mr. Esquilant in the case of silver
turbits.

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« Reply #159 on: February 10, 2009, 01:15:34 pm »

  * Dr. Chapius, Le Pigeon Voyageur Belge, 1865, p. 87.
  *(2) The Field, Sept., 1872.

  With fowls, variations of colour, limited in their transmission to
the male sex, habitually occur. When this form of inheritance
prevails, it might well happen that some of the successive
variations would be transferred to the female, who would then slightly
resemble the male, as actually occurs in some breeds. Or again, the
greater number, but not all, of the successive steps might be
transferred to both sexes, and the female would then closely
resemble the male. There can hardly be a doubt that this is the
cause of the male pouter pigeon having a somewhat larger crop, and
of the male carrier pigeon having somewhat larger wattles, than
their respective females; for fanciers have not selected one sex
more than the other, and have had no wish that these characters should
be more strongly displayed in the male than in the female, yet this is
the case with both breeds.
  The same process would have to be followed, and the same
difficulties encountered, if it were desired to make a breed with
the females alone of some new colour.
  Lastly, our fancier might wish to make a breed with the two sexes
differing from each other, and both from the parent species. Here
the difficulty would be extreme, unless the successive variations were
from the first sexually limited on both sides, and then there would be
no difficulty. We see this with the fowl; thus the two sexes of the
pencilled Hamburghs differ greatly from each other, and from the two
sexes of the aboriginal Gallus bankiva; and both are now kept constant
to their standard of excellence by continued selection, which would be
impossible unless the distinctive characters of both were limited in
their transmission.
  The Spanish fowl offers a more curious case; the male has an immense
comb, but some of the successive variations, by the accumulation of
which it was acquired, appear to have been transferred to the
female; for she has a comb many times larger than that of the
females of the parent species. But the comb of the female differs in
one respect from that of the male, for it is apt to lop over; and
within a recent period it has been ordered by the fancy that this
should always be the case, and success has quickly followed the order.
Now the lopping of the comb must be sexually limited in its
transmission, otherwise it would prevent the comb of the male from
being perfectly upright, which would be abhorrent to every fancier. On
the other hand, the uprightness of the comb in the male must
likewise be a sexually-limited character, otherwise it would prevent
the comb of the female from lopping over.
  From the foregoing illustrations, we see that even with almost
unlimited time at command, it would be an extremely difficult and
complex, perhaps an impossible process, to change one form of
transmission into the other through selection. Therefore, without
distinct evidence in each case, I am unwilling to admit that this
has been effected in natural species. On the other hand, by means of
successive variations, which were from the first sexually limited in
their transmission, there would not be the least difficulty in
rendering a male bird widely different in colour or in any other
character from the female; the latter being left unaltered, or
slightly altered, or specially modified for the sake of protection.
  As bright colours are of service to the males in their rivalry
with other males, such colours would be selected whether or not they
were transmitted exclusively to the same sex. Consequently the females
might be expected often to partake of the brightness of the males to a
greater or less degree; and this occurs with a host of species. If all
the successive variations were transmitted equally to both sexes,
the females would be indistinguishable from the males; and this
likewise occurs with many birds. If, however, dull colours were of
high importance for the safety of the female during incubation, as
with many ground birds, the females which varied in brightness, or
which received through inheritance from the males any marked accession
of brightness, would sooner or later be destroyed. But the tendency in
the males to continue for an indefinite period transmitting to their
female offspring their own brightness, would have to be eliminated
by a change in the form of inheritance; and this, as shewn by our
previous illustration, would be extremely difficult. The more probable
result of the long-continued destruction of the more brightly-coloured
females, supposing the equal form of transmission to prevail would
be the lessening or annihilation of the bright colours of the males,
owing to their continual crossing with the duller females. It would be
tedious to follow out all the other possible results; but I may remind
the reader that if sexually limited variations in brightness
occurred in the females, even if they were not in the least
injurious to them and consequently were not eliminated, yet they would
not be favoured or selected, for the male usually accepts any
female, and does not select the more attractive individuals;
consequently these variations would be liable to be lost, and would
have little influence on the character of the race; and this will
aid in accounting for the females being commonly duller-coloured
than the males.
  In the eighth chapter instances were given, to which many might here
be added, of variations occurring at various ages, and inherited at
the corresponding age. It was also shewn that variations which occur
late in life are commonly transmitted to the same sex in which they
first appear; whilst variations occurring early in life are apt to
be transmitted to both sexes; not that all the cases of
sexually-limited transmission can thus be accounted for. It was
further shewn that if a male bird varied by becoming brighter whilst
young, such variations would be of no service until the age for
reproduction had arrived, and there was competition between rival
males. But in the case of birds living on the ground and commonly in
need of the protection of dull colours, bright tints would be far more
dangerous to the young and inexperienced than to the adult males.
Consequently the males which varied in brightness whilst young would
suffer much destruction and be eliminated through natural selection;
on the other hand, the males which varied in this manner when nearly
mature, notwithstanding that they were exposed to some additional
danger, might survive, and from being favoured through sexual
selection, would procreate their kind. As a relation often exists
between the period of variation and the form of transmission, if the
bright-coloured young males were destroyed and the mature ones were
successful in their courtship, the males alone would acquire brilliant
colours and would transmit them exclusively to their male offspring.
But I by no means wish to maintain that the influence of age on the
form of transmission, is the sole cause of the great difference in
brilliancy between the sexes of many birds.
  When the sexes of birds differ in colour, it is interesting to
determine whether the males alone have been modified by sexual
selection, the females having been left unchanged, or only partially
and indirectly thus changed; or whether the females have been
specially modified through natural selection for the sake of
protection. I will therefore discuss this question at some length,
even more fully than its intrinsic importance deserves; for various
curious collateral points may thus be conveniently considered.
  Before we enter on the subject of colour, more especially in
reference to Mr. Wallace's conclusions, it may be useful to discuss
some other sexual differences under a similar point of view. A breed
of fowls formerly existed in Germany* in which the hens were furnished
with spurs; they were good layers, but they so greatly disturbed their
nests with their spurs that they could not be allowed to sit on
their own eggs. Hence at one time it appeared to me probable that with
the females of the wild Gallinaceae the development of spurs had
been checked through natural selection, from the injury thus caused to
their nests. This seemed all the more probable, as wing-spurs, which
would not be injurious during incubation, are often as well
developed in the female as in the male; though in not a few cases they
are rather larger in the male. When the male is furnished with
leg-spurs the female almost always exhibits rudiments of them,- the
rudiment sometimes consisting of a mere scale, as in Gallus. Hence
it might be argued that the females had aboriginally been furnished
with well-developed spurs, but that these had subsequently been lost
through disuse or natural selection. But if this view be admitted,
it would have to be extended to innumerable other cases; and it
implies that the female progenitors of the existing spur-bearing
species were once encumbered with an injurious appendage.

  * Bechstein, Naturgeschichte Deutschlands, 1793, B. iii., 339.

  In some few genera and species, as in Galloperdix, Acomus, and the
Javan peacock (Pavo muticus), the females, as well as the males,
possess well-developed leg-spurs. Are we to infer from this fact
that they construct a different sort of nest from that made by their
nearest allies, and not liable to be injured by their spurs; so that
the spurs have not been removed? Or are we to suppose that the females
of these several species especially require spurs for their defence?
It is a more probable conclusion that both the presence and absence of
spurs in the females result from different laws of inheritance
having prevailed, independently of natural selection. With the many
females in which spurs appear as rudiments, we may conclude that
some few of the successive variations, through which they were
developed in the males, occurred very early in life, and were
consequently transferred to the females. In the other and much rarer
cases, in which the females possess fully developed spurs, we may
conclude that all the successive variations were transferred to
them; and that they gradually acquired and inherited the habit of
not disturbing their nests.
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« Reply #160 on: February 10, 2009, 01:15:46 pm »

The vocal organs and the feathers variously modified for producing
sound, as well as the proper instincts for using them, often differ in
the two sexes, but are sometimes the same in both. Can such
differences be accounted for by the males having acquired these organs
and instincts, whilst the females have been saved from inheriting
them, on account of the danger to which they would have been exposed
by attracting the attention of birds or beasts of prey? This does
not seem to me probable, when we think of the multitude of birds which
with impunity gladden the country with their voices during the
spring.* It is a safer conclusion that, as vocal and instrumental
organs are of special service only to the males during their
courtship, these organs were developed through sexual selection and
their constant use in that sex alone- the successive variations and
the effects of use having been from the first more or less limited
in transmission to the male offspring.

  * Daines Barrington, however, thought it probable (Philosophical
Transactions, 1773, p. 164) that few female birds sing, because the
talent would have been dangerous to them during incubation. He adds,
that a similar view may possibly account for the inferiority of the
female to the male in plumage.

  Many analogous cases could be adduced; those for instance of the
plumes on the head being generally longer in the male than in the
female, sometimes of equal length in both sexes, and occasionally
absent in the female,- these several cases occurring in the same group
of birds. It would be difficult to account for such a difference
between the sexes by the female having been benefited by possessing
a slightly shorter crest than the male, and its consequent
diminution or complete suppression through natural selection. But I
will take a more favourable case, namely the length of the tail. The
long train of the peacock would have been not only inconvenient but
dangerous to the peahen during the period of incubation and whilst
accompanying her young. Hence there is not the least a priori
improbability in the development of her tail having been checked
through natural selection. But the females of various pheasants, which
apparently are exposed on their open nests to as much danger as the
peahen, have tails of considerable length. The females as well as
the males of the Menura superba have long tails, and they build a
domed nest, which is a great anomaly in so large a bird. Naturalists
have wondered how the female Menura could manage her tail during
incubation; but it is now known* that she "enters the nest head first,
and then turns round with her tail sometimes over her back, but more
often bent round by her side. Thus in time the tail becomes quite
askew, and is a tolerable guide to the length of time the bird has
been sitting." Both sexes of an Australian kingfisher (Tanysiptera
sylvia) have the middle tail-feathers greatly lengthened, and the
female makes her nest in a hole; and as I am informed by Mr. R. B.
Sharpe these feathers become much crumpled during incubation.

  * Mr. Ramsay, in Proc. Zoolog. Soc., 1868, p. 50.

  In these two latter cases the great length of the tail-feathers must
be in some degree inconvenient to the female; and as in both species
the tail-feathers of the female are somewhat shorter than those of the
male, it might be argued that their full development had been
prevented through natural selection. But if the development of the
tail of the peahen had been checked only when it became inconveniently
or dangerously great, she would have retained a much longer tail
than she actually possesses; for her tail is not nearly so long,
relatively to the size of her body, as that of many female
pheasants, nor longer than that of the female turkey. It must also
be borne in mind that, in accordance with this view, as soon as the
tail of the peahen became dangerously long, and its development was
consequently checked, she would have continually reacted on her male
progeny, and thus have prevented the peacock from acquiring his
present magnificent train. We may therefore infer that the length of
the tail in the peacock and its shortness in the peahen are the result
of the requisite variations in the male having been from the first
transmitted to the male offspring alone.
  We are led to a nearly similar conclusion with respect to the length
of the tail in the various species of pheasants. In the Eared pheasant
(Crossoptilon auritum) the tail is of equal length in both sexes,
namely sixteen or seventeen inches; in the common pheasant it is about
twenty inches long in the male and twelve in the female; in
Soemmerring's pheasant, thirty-seven inches in the male and only eight
in the female; and lastly in Reeve's pheasant it is sometimes actually
seventy-two inches long in the male and sixteen in the female. Thus in
the several species, the tail of the female differs much in length,
irrespectively of that of the male; and this can be accounted for,
as it seems to me, with much more probability, by the laws of
inheritance,- that is by the successive variations having been from
the first more or less closely limited in their transmission to the
male sex than by the agency of natural selection, resulting from the
length of tail being more or less injurious to the females of these
several allied species.

  We may now consider Mr. Wallace's arguments in regard to the
sexual colouration of birds. He believes that the bright tints
originally acquired through sexual selection by the males would in
all, or almost all cases, have been transmitted to the females, unless
the transference had been checked through natural selection. I may
here remind the reader that various facts opposed to this view have
already been given under reptiles, amphibians, fishes and lepidoptera.
Mr. Wallace rests his belief chiefly, but not exclusively, as we shall
see in the next chapter, on the following statement,* that when both
sexes are coloured in a very conspicuous manner, the nest is of such a
nature as to conceal the sitting bird; but when there is a marked
contrast of colour between the sexes, the male being gay and the
female dull-coloured, the nest is open and exposes the sitting bird to
view. This coincidence, as far as it goes, certainly seems to favour
the belief that the females which sit on open nests have been
specially modified for the sake of protection; but we shall
presently see that there is another and more probable explanation,
namely, that conspicuous females have acquired the instinct of
building domed nests oftener than dull-coloured birds. Mr. Wallace
admits that there are, as might have been expected, some exceptions to
his two rules, but it is a question whether the exceptions are not
so numerous as seriously to invalidate them.

  * Journal of Travel, edited by A. Murray, vol. i., 1868, p. 78.

  There is in the first place much truth in the Duke of Argyll's
remark* that a large domed nest is more conspicuous to an enemy,
especially to all tree-haunting carnivorous animals, than a smaller
open nest. Nor must we forget that with many birds which build open
nests, the male sits on the eggs and aids the female in feeding the
young: this is the case, for instance, with Pyranga aestiva,*(2) one
of the most splendid birds in the United States, the male being
vermilion, and the female light brownish-green. Now if brilliant
colours had been extremely dangerous to birds whilst sitting on
their open nests, the males in these cases would have suffered
greatly. It might, however, be of such paramount importance to the
male to be brilliantly coloured, in order to beat his rivals, that
this may have more than compensated some additional danger.

  * Journal of Travel, edited by A. Murray, vol. i., 1868, p. 281.
  *(2) Audubon, Ornithological Biography, vol. i., p. 233.

  Mr. Wallace admits that with the king-crows (Dicrurus), orioles, and
Pittidae, the females are conspicuously coloured, yet build open
nests; but he urges that the birds of the first group are highly
pugnacious and could defend themselves; that those of the second group
take extreme care in concealing their open nests, but this does not
invariably hold good;* and that with the birds of the third group
the females are brightly coloured chiefly on the under surface.
Besides these cases, pigeons which are sometimes brightly, and
almost always conspicuously coloured, and which are notoriously liable
to the attacks of birds of prey, offer a serious exception to the
rule, for they almost always build open and exposed nests. In
another large family, that of the humming-birds, all the species build
open nests, yet with some of the most gorgeous species the sexes are
alike; and in the majority, the females, though less brilliant than
the males, are brightly coloured. Nor can it be maintained that all
female humming-birds, which are brightly coloured, escape detection by
their tints being green, for some display on their upper surfaces red,
blue, and other colours.*(2)

  * Jerdon, Birds of India, vol. ii., p. 108. Gould's Handbook of
the Birds of Australia, vol. i., p. 463.
  *(2) For instance, the female Eupetomena macroura has the head and
tail dark blue with reddish loins; the female Lampornis porphyrurus is
blackish-green on the upper surface, with the lores and sides of the
throat crimson; the female Eulampis jugularis has the top of the
head and back green, but the loins and the tail are crimson. Many
other instances of highly conspicuous females could be given. See
Mr. Gould's magnificent work on this family.

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« Reply #161 on: February 10, 2009, 01:16:06 pm »

In regard to birds which build in holes or construct domed nests,
other advantages, as Mr. Wallace remarks, besides concealment are
gained, such as shelter from the rain, greater warmth, and in hot
countries protection from the sun;* so that it is no valid objection
to his view that many birds having both sexes obscurely coloured build
concealed nests.*(2) The female horn-bill (Buceros), for instance,
of India and Africa is protected during incubation with
extraordinary care, for she plasters up with her own excrement the
orifice of the hole in which she sits on her eggs, leaving only a
small orifice through which the male feeds her; she is thus kept a
close prisoner during the whole period of incubation;*(3) yet female
horn-bills are not more conspicuously coloured than many other birds
of equal size which build open nests. It is a more serious objection
to Mr. Wallace's view, as is admitted by him, that in some few
groups the males are brilliantly coloured and the females obscure, and
yet the latter hatch their eggs in domed nests. This is the case
with the Grallinae of Australia, the superb warblers (Maluridae) of
the same country, the sun-birds (Nectariniae), and with several of the
Australian honey-suckers or Meliphagidae.*(4)

  * Mr. Salvin noticed in Guatemala (Ibis, 1864, p. 375) that
humming-birds were much more unwilling to leave their nests during
very hot weather, when the sun was shining brightly, as if their
eggs would be thus injured, than during cool, cloudy, or rainy
weather.
  *(2) I may specify, as instances of dull-coloured birds building
concealed nests, the species belonging to eight Australian genera
described in Gould's Handbook of the Birds of Australia, vol. i.,
pp. 340, 362, 365, 383, 387, 389, 391, 414.
  *(3) Mr. C. Horne, Proc. Zoolog. Soc., 1869. p. 243.
  *(4) On the nidification and colours of these latter species, see
Gould's Handbook of the Birds of Australia, vol. i., pp. 504, 527.

  If we look to the birds of England we shall see that there is no
close and general relation between the colours of the female and the
nature of the nest which is constructed. About forty of our British
birds (excluding those of large size which could defend themselves)
build in holes in banks, rocks, or trees, or construct domed nests. If
we take the colours of the female goldfinch, bullfinch, or black-bird,
as a standard of the degree of conspicuousness, which is not highly
dangerous to the sitting female, then out of the above forty birds the
females of only twelve can be considered as conspicuous to a dangerous
degree, the remaining twenty-eight being inconspicuous.* Nor is
there any close relation within the same genus between a
well-pronounced difference in colour between the sexes, and the nature
of the nest constructed. Thus the male house sparrow (Passer
domesticus) differs much from the female, the male tree-sparrow (P.
montanus) hardly at all, and yet both build well-concealed nests.
The two sexes of the common fly-catcher (Muscicapa grisola) can hardly
be distinguished, whilst the sexes of the pied fly-catcher (M.
luctuosa) differ considerably, and both species build in holes or
conceal their nests. The female blackbird (Turdus merula) differs
much, the female ring-ouzel (T. torquatus) differs less, and the
female common thrush (T. musicus) hardly at all from their
respective males; yet all build open nests. On the other hand, the not
very distantly-allied water-ouzel (Cinclus aquaticus) builds a domed
nest, and the sexes differ about as much as in the ring-ouzel. The
black and red grouse (Tetrao tetrix and T. scoticus) build open
nests in equally well-concealed spots, but in the one species the
sexes differ greatly, and in the other very little.

  * I have consulted, on this subject, Macgillivray's British Birds,
and though doubts may be entertained in some cases in regard to the
degree of concealment of the nest, and to the degree of
conspicuousness of the female, yet the following birds, which all
lay their eggs in holes or in domed nests, can hardly be considered,
by the above standard, as conspicuous: Passer, 2 species; Sturnus,
of which the female is considerably less brilliant than the male;
Cinclus; Motallica boarula (?); Erithacus (?); Fruticola, 2 sp.;
Saxicola; Ruticilla, 2 sp.; Sylvia, 3 sp.; Parus, 3 sp.; Mecistura
anorthura; Certhia; Sitta; Yunx; Muscicapa, 2 sp.; Hirundo, 3 sp.; and
Cypselus. The females of the following 12 birds may be considered as
conspicuous according to the same standard, viz., Pastor, Motacilla
alba, Parus major and P. caeruleus, Upupa, Picus, 4 sp., Coracias,
Alcedo, and Merops.

  Notwithstanding the foregoing objections, I cannot doubt, after
reading Mr. Wallace's excellent essay, that looking to the birds of
the world, a large majority of the species in which the females are
conspicuously coloured (and in this case the males with rare
exceptions are equally conspicuous), build concealed nests for the
sake of protection. Mr. Wallace enumerates* a long series of groups in
which this rule bolds good; but it will suffice here to give, as
instances, the more familiar groups of kingfishers, toucans,
trogons, puff-birds (Capitonidae), plantain-eaters (Musophagae,
woodpeckers, and parrots. Mr. Wallace believes that in these groups,
as the males gradually acquired through sexual selection their
brilliant colours, these were transferred to the females and were
not eliminated by natural selection, owing to the protection which
they already enjoyed from their manner of nidification. According to
this view, their present manner of nesting was acquired before their
present colours. But it seems to me much more probable that in most
cases, as the females were gradually rendered more and more
brilliant from partaking of the colours of the male, they were
gradually led to change their instincts (supposing that they
originally built open nests), and to seek protection by building domed
or concealed nests. No one who studies, for instance, Audubon's
account of the differences in the nests of the same species in the
northern and southern United States,*(2) will feel any great
difficulty in admitting that birds, either by a change (in the
strict sense of the word) of their habits, or through the natural
selection of so-called spontaneous variations of instinct, might
readily be led to modify their manner of nesting.

  * Journal of Travel, edited by A. Murray, vol. i., p. 78.
  *(2) See many statements in the Ornithological Biography. See also
some curious observations on the nests of Italian birds by Eugenio
Bettoni, in the Atti della Societa Italiana, vol. xi., 1869, p. 487.

  This way of viewing the relation, as far as it holds good, between
the bright colours of female birds and their manner of nesting,
receives some support from certain cases occurring in the Sahara
Desert. Here, as in most other deserts, various birds, and many
other animals, have had their colours adapted in a wonderful manner to
the tints of the surrounding surface. Nevertheless there are, as I
am informed by the Rev. Mr. Tristram, some curious exceptions to the
rule; thus the male of the Monticola cyanea is conspicuous from his
bright blue colour, and the female almost equally conspicuous from her
mottled brown and white plumage; both sexes of two species of
Dromolaea are of a lustrous black; so that these three species are far
from receiving protection from their colours, yet they are able to
survive, for they have acquired the habit of taking refuge from danger
in holes or crevices in the rocks.
  With respect to the above groups in which the females are
conspicuously coloured and build concealed nests, it is not
necessary to suppose that each separate species had its nidifying
instinct specially modified; but only that the early progenitors of
each group were gradually led to build domed or concealed nests, and
afterwards transmitted this instinct, together with their bright
colours, to their modified descendants. As far as it can be trusted,
the conclusion is interesting, that sexual selection together with
equal or nearly equal inheritance by both sexes, have indirectly
determined the manner of nidification of whole groups of birds.
  According to Mr. Wallace, even in the groups in which the females,
from being protected in domed nests during incubation, have not had
their bright colours eliminated through natural selection, the males
often differ in a slight, and occasionally in a considerable degree
from the females. This is a significant fact, for such differences
in colour must be accounted for by some of the variations in the males
having been from the first limited in transmission to the same sex; as
it can hardly be maintained that these differences, especially when
very slight, serve as a protection to the female. Thus all the species
in the splendid group of the trogons build in holes; and Mr. Gould
gives figures* of both sexes of twenty-five species, in all of
which, with one partial exception, the sexes differ sometimes
slightly, sometimes conspicuously, in colour,- the males being
always finer than the females, though the latter are likewise
beautiful. All the species of kingfishers build in holes, and with
most of the species the sexes are equally brilliant, and thus far
Mr. Wallace's rule holds good; but in some of the Australian species
the colours of the females are rather less vivid than those of the
male; and in one splendidly-coloured species, the sexes differ so much
that they were at first thought to be specifically distinct.*(2) Mr.
R. B. Sharpe, who has especially studied this group, has shewn me some
American species (Ceryle) in which the breast of the male is belted
with black. Again, in Carcineutes, the difference between the sexes is
conspicuous: in the male the upper surface is dull-blue banded with
black, the lower surface being partly fawn-coloured, and there is much
red about the head; in the female the upper surface is reddish-brown
banded with black, and the lower surface white with black markings
It is an interesting fact, as shewing how the same peculiar style of
sexual colouring often characterises allied forms, that in three
species of Dacelo the male differs from the female only in the tail
being dull-blue banded with black, whilst that of the female is
brown with blackish bars; so that here the tail differs in colour in
the two sexes in exactly the same manner as the whole upper surface in
the two sexes of Carcineutes.
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« Reply #162 on: February 10, 2009, 01:17:29 pm »

* See his Monograph of the Trogonidae, 1st edition.
  *(2) Namely, Cyanalcyon. Gould's Handbook of the Birds of Australia,
vol. i., p. 133; see, also, pp. 130, 136.

  With parrots, which likewise build in holes, we find analogous
cases: in most of the species, both sexes are brilliantly coloured and
indistinguishable, but in not a few species the males are coloured
rather more vividly than the females, or even very differently from
them. Thus, besides other strongly-marked differences, the whole under
surface of the male king lory (Aprosmictus scapulatus) is scarlet,
whilst the throat and chest of the female is green tinged with red: in
the Euphema splendida there is a similar difference, the face and wing
coverts moreover of the female being of a paler blue than in the
male.* In the family of the **** (Parinae), which build concealed
nests, the female of our common blue tomtit (Parus caeruleus), is
"much less brightly coloured" than the male: and in the magnificent
sultan yellow tit of India the difference is greater.*(2)

  * Every gradation of difference between the sexes may be followed in
the parrots of Australia. See Gould, op. cit., vol. ii., pp. 14-102.
  *(2) Macgillivray's British Birds, vol. ii., p. 433. Jerdon, Birds
of India, vol. ii., p. 282.

  Again, in the great group of the woodpeckers,* the sexes are
generally nearly alike, but in the Megapicus validus all those parts
of the head, neck, and breast, which are crimson in the male are
pale brown in the female. As in several woodpeckers the head of the
male is bright crimson, whilst that of the female is plain, it
occurred to me that this colour might possibly make the female
dangerously conspicuous, whenever she put her head out of the hole
containing her nest, and consequently that this colour, in
accordance with Mr. Wallace's belief, had been eliminated. This view
is strengthened by what Malherbe states with respect to Indopicus
carlotta; namely, that the young females, like the young males, have
some crimson about their heads, but that this colour disappears in the
adult female, whilst it is intensified in the adult male. Nevertheless
the following considerations render this view extremely doubtful:
the male takes a fair share in incubation,*(2) and would be thus
almost equally exposed to danger; both sexes of many species have
their heads of an equally bright crimson; in other species the
difference between the sexes in the amount of scarlet is so slight
that it can hardly make any appreciable difference in the danger
incurred; and lastly, the colouring of the head in the two sexes often
differs slightly in other ways.

  * All the following facts are taken from M. Malherbe's magnificent
Monographie des Picidees, 1861.
  *(2) Audubon's Ornithological Biography, vol. ii., p. 75; see also
the Ibis, vol. i., p. 268.

  The cases, as yet given, of slight and graduated differences in
colour between the males and females in the groups, in which as a
general rule the sexes resemble each other, all relate to species
which build domed or concealed nests. But similar gradations may
likewise be observed in groups in which the sexes as a general rule
resemble each other, but which build open nests.
  As I have before instanced the Australian parrots, so I may here
instance, without giving any details, the Australian pigeons.* It
deserves especial notice that in all these cases the slight
differences in plumage between the sexes are of the same general
nature as the occasionally greater differences. A good illustration of
this fact has already been afforded by those kingfishers in which
either the tail alone or the whole upper surface of the plumage
differs in the same manner in the two sexes. Similar cases may be
observed with parrots and pigeons. The differences in colour between
the sexes of the same species are, also, of the same general nature as
the differences in colour between the distinct species of the same
group. For when in a group in which the sexes are usually alike, the
male differs considerably from the female, he is not coloured in a
quite new style. Hence we may infer that within the same group the
special colours of both sexes when they are alike, and the colours
of the male, when he differs slightly or even considerably from the
female, have been in most cases determined by the same general
cause; this being sexual selection.

  * Gould's Handbook of the Birds of Australia, vol. ii., pp. 109-149.

  It is not probable, as has already been remarked, that differences
in colour between the sexes, when very slight, can be of service to
the female as a protection. Assuming, however, that they are of
service, they might be thought to be cases of transition; but we
have no reason to believe that many species at any one time are
undergoing change. Therefore we can hardly admit that the numerous
females which differ very slightly in colour from their males are
now all commencing to become obscure for the sake of protection.
Even if we consider somewhat more marked sexual differences, is it
probable, for instance, that the head of the female chaffinch,- the
crimson on the breast of the female bullfinch,- the green of the
female greenfinch,- the crest of the female golden-crested wren,
have all been rendered less bright by the slow process of selection
for the sake of protection? I cannot think so; and still less with the
slight differences between the sexes of those birds which build
concealed nests. On the other hand, the differences in colour
between the sexes, whether great or small, may to a large extent be
explained on the principle of the successive variations, acquired by
the males through sexual selection, having been from the first more or
less limited in their transmission to the females. That the degree
of limitation should differ in different species of the same group
will not surprise any one who has studied the laws of inheritance, for
they are so complex that they appear to us in our ignorance to be
capricious in their action.*
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« Reply #163 on: February 10, 2009, 01:17:43 pm »

* See remarks to this effect in Variation of Animals and Plants
under Domestication, vol. ii., chap. xii.

  As far as I can discover there are few large groups of birds in
which all the species have both sexes alike and brilliantly
coloured, but I hear from Mr. Sclater, that this appears to be the
case with the Musophagae or plantain-eaters. Nor do I believe that any
large group exists in which the sexes of all the species are widely
dissimilar in colour: Mr. Wallace informs me that the chatterers of S.
America (Cotingidae) offer one of the best instances; but with some of
the species, in which the male has a splendid red breast, the female
exhibits some red on her breast; and the females of other species shew
traces of the green and other colours of the males. Nevertheless we
have a near approach to close sexual similarity or dissimilarity
throughout several groups: and this, from what has just been said of
the fluctuating nature of inheritance, is a somewhat surprising
circumstance. But that the same laws should largely prevail with
allied animals is not surprising. The domestic fowl has produced a
great number of breeds and sub-breeds, and in these the sexes
generally differ in plumage; so that it has been noticed as an unusual
circumstance when in certain sub-breeds they resemble each other. On
the other hand, the domestic pigeon has likewise produced a vast
number of distinct breeds and sub-breeds, and in these, with rare
exceptions, the two sexes are identically alike.
  Therefore if other species of Gallus and Columba were domesticated
and varied, it would not be rash to predict that similar rules of
sexual similarity and dissimilarity, depending on the form of
transmission, would hold good in both cases. In like manner the same
form of transmission has generally prevailed under nature throughout
the same groups, although marked exceptions to this rule occur. Thus
within the same family or even genus, the sexes may be identically
alike, or very different in colour. Instances have already been
given in the same genus, as with sparrows, flycatchers, thrushes and
grouse. In the family of pheasants the sexes of almost all the species
are wonderfully dissimilar, but are quite alike in the eared
pheasant or Crossoptilon auritum. In two species of Chloephaga, a
genus of geese, the male cannot be distinguished from the females,
except by size; whilst in two others, the sexes are so unlike that
they might easily be mistaken for distinct species.*

  * The Ibis, vol. vi., 1864, p. 122.

  The laws of inheritance can alone account for the following cases,
in which the female acquires, late in life, certain characters
proper to the male, and ultimately comes to resemble him more or
less completely. Here protection can hardly have come into play. Mr.
Blyth informs me that the females of Oriolus melanocephalus and of
some allied species, when sufficiently mature to breed, differ
considerably in plumage from the adult males; but after the second
or third moults they differ only in their beaks having a slight
greenish tinge. In the dwarf bitterns (Ardetta), according to the same
authority, "the male acquires his final livery at the first moult, the
female not before the third or fourth moult; in the meanwhile she
presents an intermediate garb, which is ultimately exchanged for the
same livery as that of the male." So again the female Falco peregrinus
acquires her blue plumage more slowly than the male. Mr. Swinhoe
states that with one of the drongo shrikes (Dicrurus macrocercus)
the male, whilst almost a nestling, moults his soft brown plumage
and becomes of a uniform glossy greenish-black; but the female retains
for a long time the white striae and spots on the axillary feathers;
and does not completely assume the uniform black colour of the male
for three years. The same excellent observer remarks that in the
spring of the second year the female spoon-bill (Platalea) of China
resembles the male of the first year, and that apparently it is not
until the third spring that she acquires the same adult plumage as
that possessed by the male at a much earlier age. The female
Bombycilla carolinensis differs very little from the male, but the
appendages, which like beads of red sealing-wax ornament the
wing-feathers,* are not developed in her so early in life as in the
male. In the male of an Indian parrakeet (Paloeornis javanicus) the
upper mandible is coral-red from his earliest youth, but in the
female, as Mr. Blyth has observed with caged and wild birds, it is
at first black and does not become red until the bird is at least a
year old, at which age the sexes resemble each other in all
respects. Both sexes of the wild turkey are ultimately furnished
with a tuft of bristles on the breast, but in two-year-old birds the
tuft is about four inches long in the male and hardly apparent in
the female; when, however, the latter has reached her fourth year,
it is from four to five inches in length.*(2)

  * When the male courts the female, these ornaments are vibrated, and
"are shewn off to great advantage," on the outstretched wings: A.
Leith Adams, Field and Forest Rambles, 1873, p. 153.
  *(2) On Ardetta, Translation of Cuvier's Regne Animal, by Mr. Blyth,
footnote, p. 159. On the peregrine falcon, Mr. Blyth, in
Charlesworth's Mag. of Nat. Hist., vol. i., 1837, p. 304. On Dicrurus,
Ibis, 1863, p. 44. On the Platalea, Ibis, vol. vi., 1864, p. 366. On
the Bombycilla, Audubon's Ornitholog. Biography, vol. i., p. 229. On
the Palaeornis, see, also, Jerdon, Birds of India, vol. i., p. 263. On
the wild turkey, Audubon, ibid., vol. i., p. 15; but I hear from Judge
Caton that in Illinois the female very rarely acquires a tuft.
Analogous cases with the females of Petrcocssyphus are given by Mr. R.
Sharpe, Proeedings of the Zoological Society, 1872, p. 496.

  These cases must not be confounded with those where diseased or
old females abnormally assume masculine characters, nor with those
where fertile females, whilst young, acquire the characters of the
male, through variation or some unknown cause.* But all these cases
have so much in common that they depend, according to the hypothesis
of pangenesis, on gemmules derived from each part of the male being
present, though latent, in the female; their development following
on some slight change in the elective affinities of her constituent
tissues.

  * Of these latter cases Mr. Blyth has recorded (Translation of
Cuvier's Regne Animal, p. 158) various instances with Lanius,
Ruticilla, Linaria, and Anas. Audubon has also recorded a similar case
(Ornitholog. Biography, vol. v., p. 519) with Pyranga aestiva.

  A few words must be added on changes of plumage in relation to the
season of the year. From reasons formerly assigned there can be little
doubt that the elegant plumes, long pendant feathers, crests, &c.,
of egrets, herons, and many other birds, which are developed and
retained only during the summer, serve for ornamental and nuptial
purposes, though common to both sexes. The female is thus rendered
more conspicuous during the period of incubation than during the
winter; but such birds as herons and egrets would be able to defend
themselves. As, however, plumes would probably be inconvenient and
certainly of no use during the winter, it is possible that the habit
of moulting twice in the year may have been gradually acquired through
natural selection for the sake of casting off inconvenient ornaments
during the winter. But this view cannot be extended to the many
waders, whose summer and winter plumages differ very little in colour.
With defenceless species, in which both sexes, or the males alone,
become extremely conspicuous during the breeding-season,- or when
the males acquire at this season such long wing or tail-feathers as to
impede their flight, as with Cosmetornis and Vidua,- it certainly at
first appears highly probable that the second moult has been gained
for the special purpose of throwing off these ornaments. We must,
however, remember that many birds, such as some of the birds of
paradise, the Argus pheasant and peacock, do not cast their plumes
during the winter; and it can hardly be maintained that the
constitution of these birds, at least of the Gallinaceae, renders a
double moult impossible, for the ptarmigan moults thrice in the year.*
Hence it must be considered as doubtful whether the many species which
moult their ornamental plumes or lose their bright colours during
the winter, have acquired this habit on account of the inconvenience
or danger which they would otherwise have suffered.
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« Reply #164 on: February 10, 2009, 01:18:01 pm »

* See Gould's Birds of Great Britain.

  I conclude, therefore, that the habit of moulting twice in the
year was in most or all cases first acquired for some distinct
purpose, perhaps for gaining a warmer winter covering; and that
variations in the plumage occurring during the summer were accumulated
through sexual selection, and transmitted to the offspring at the same
season of the year; that such variations were inherited either by both
sexes or by the males alone, according to the form of inheritance
which prevailed. This appears more probable than that the species in
all cases originally tended to retain their ornamental plumage
during the winter, but were saved from this through natural selection,
resulting from the inconvenience or danger thus caused.

  I have endeavoured in this chapter to shew that the arguments are
not trustworthy in favour of the view that weapons, bright colours,
and various ornaments, are now confined to the males owing to the
conversion, by natural selection, of the equal transmission of
characters to both sexes, into transmission to the male sex alone.
It is also doubtful whether the colours of many female birds are due
to the preservation, for the sake of protection, of variations which
were from the first limited in their transmission to the female sex.
But it will be convenient to defer any further discussion on this
subject until I treat, in the following chapter, of the differences in
plumage between the young and old.



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