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Bullseye
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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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