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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. 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. * 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 tits (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.* * 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 |
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