The Zoologist/4th series, vol 3 (1899)/Issue 694/The Coloration of British Birds and Their Eggs, Storrs Fox

by William Storrs Fox

 

THE COLORATION OF BRITISH BIRDS AND THEIR EGGS.

By W. Storrs Fox, M.A., F.Z.S.

 

Some three years ago I made a rough table of the coloration of British birds and their eggs. I did this for the benefit of a local Naturalists' Club. Last year I had reason to revise this table. As I do not know of the existence of anything on quite similar lines, it has struck me that it may be of interest to some of the readers of 'The Zoologist.'

In dealing with coloration it stands to reason that there cannot be one law for birds found in the British Islands, and another which applies to those inhabiting the rest of the world. But, being more familiar with our own birds, I have drawn my illustrations from them almost entirely. I believe that the principles laid down in this paper are of universal application, and that the interest attached to them will not be lessened by the fact that the examples given are taken from a small group of islands.

The introduction to the second volume of Seebohm's 'British Birds' consists of an account by Mr. Charles Dixon of the protective colour of eggs. The subject is there dealt with at some length. Dr. A.R. Wallace, when treating of the coloration of birds' eggs, refers to that "valuable work."^[1] Mr. Dixon has collected a number of very interesting facts, and everyone interested in the subject ought to read his account.

It will be seen from the two following tables that certain general principles govern the colours of both birds and their eggs. There are, however, some very awkward exceptions to the rule. Perhaps someone will throw light upon these difficulties. When it is clear that eggs are usually protectively coloured, it is strange that we ever should come across any which lack such protection. So also with the birds themselves, it is difficult to see why the cock Song-Thrush should be protectively coloured, but the cock Blackbird conspicuous on account of his intense black plumage. I am not aware that the former assists in incubating the eggs, and that the latter does not perform any such office. It is obvious that certain birds have little or no need of protectively coloured plumage. Some are naturally protected by their size and strength, e.g. the Swan; others by size combined with gregarious habits, as the Rook and Heron; or, by these defences combined with great powers of diving, as the Cormorant and Guillemot. Birds, except very small ones, which nest in holes can dispense with protective colours. It may fairly be said that the position and structure of the nests regulate the colouring of the birds themselves as well as their eggs, and that wherever there is no special need for sombre shades of plumage, conspicuous or bright hues prevail.

I. Of birds which make open nests, either (a) both sexes are protectively coloured; or (b) the hen so coloured and the cock more showy.

It will be readily seen that small birds, and birds frequenting very exposed places, specially need protection. It is such birds which have both sexes protectively coloured, e.g. Song-Thrush, Hedge-Sparrow, Lark, smaller Game-birds, Rails, Plovers, Sandpipers. Certain species of the last-named group have the sexes different.

That the hen should be sombre but the cock conspicuous is not surprising in large birds, such as Ducks and the larger Game-birds. But in a less degree it holds good also in the case of many small birds, such as the Blackbird, Blackcap, Wagtails, some of the Finches, and Buntings; but in all these (except the Blackbird) the colouring of the upper parts tends to harmonize with their surroundings.

Among the Plovers and Sandpipers the Dotterel (Charadrius morinellus) and Phalarope (Phalaropus hyperboreus) may be mentioned as exceptional, for with them the female is more brightly coloured than the male. The explanation lies in the fact that these males perform the duties of incubation.

Most sea-birds are equally showily coloured in both sexes. They nearly all have pure white under parts, which strongly contrast with the grey or black of their upper parts; as, for instance, Terns, Auks, Gulls, Divers, Grebes.

Here it must be pointed out that (1) parts of plumage which are never displayed are dull-coloured; (2) parts which are out of sight when the birds are at rest, but which appear during flight, or under excitement, are often ornamented with beautiful colours or patterns. Examples may be found among Pheasants and Sandpipers. Conspicuous marks exposed during flight possibly act as danger signals.^[2] Probably all such showy colours and patterns are made use of in courtship and in battle.

The larger Gulls take three or four years before they attain to mature plumage. The plumage of quite young Gulls is sombre. The stages through which they pass before arriving at maturity are supposed to be recapitulations of former states of colouring.^[3]

II. Birds which nest in holes.

As a rule, both sexes of such birds have conspicuous plumage; as Woodpecker, Kingfisher, Sheldrake; and, among foreign birds, Parrot, Toucan. But small birds, such as Tits, Nuthatch, are much less brightly coloured than larger ones.

There are some noticeable exceptions to this rule. In the case of the Wheatears and Redstarts, the hens are sombre in colour, and the cocks much more striking looking. According to my own experience of Saxicola œnanthe and Ruticilla phœnicurus, they place their nests quite out of sight. I have very little acquaintance with the other members of these genera, but, so far as I can gather, the nests of some species are usually quite hidden, whereas those of others may be as much open to view as are many nests of the Pied Wagtail. Is it possible that with our common Wheatear and Redstart the sombre hues of the hens' plumage date back to a time when the nest was always more exposed to view?

The Wryneck and many of the Petrels are also exceptions, as both sexes are clad in dull-coloured garb. I know of no satisfactory explanation.

III. All British birds which build covered nests have both sexes alike, and are sombre in colouring. They are small defenceless birds, such as the Wren, Willow-Warbler, and Dipper.

IV. Nocturnal birds, e.g. Nightjar, Owl, have plumage which will conceal them during the day. At first sight the Barn Owl would seem to be an exception, but this species is much more retiring than most of the others, and hides away entirely out of sight.

V. The usually dull colours of the Accipitres may help these birds to escape the notice of their prey. Such an explanation is not very satisfactory, as they do not sit still and wait for their prey to approach them. But, as these birds are well able to take care of themselves, they might be expected to have brightcoloured plumage.

There are certain individual cases which are very difficult to explain:—

(a) Why is the common Swift (Cypselus apus) such a sombre-looking bird?

(b) Does the Cuckoo (Cuculus canorus) really mimic a Hawk? There are other members of this family which appear to mimic species which are not allied to them.

(c) How is the Egret (Ardea garzetta) protected? It is not large, and has pure white plumage. Is its beak a sufficient means of defence?

(d) Ruffs (Machetes pugnax) are adorned with variously coloured plumes about the neck. They go through a form of battle for the Reeves. Such characteristics are contrary to the rule of the family (Scolopacidæ) to which they belong. By way of explanation, Darwin^[4] states that the males of this species are probably polygamous.

(e) The plumage of the hen Oriole (Oriolus galbula) and the Jay (Garrulus glandarius) is quite bright enough to be conspicuous. But they nest among the thickest foliage.

 

Just as the coloration of birds' plumage falls naturally into divisions depending upon the nesting habits of the species concerned, so also may their eggs be grouped on similar lines. And moreover, the less important divisions also correspond in both cases. But when we are considering eggs laid in open nests, it is necessary to remember that such nests are nearly always partially covered by overhanging leaves and branches, by a projection of rock or stone, by thick herbage, or by sedges and long grasses. This fact will often account for the deeper or paler shades of egg-colouring.

I. Eggs laid in open nests are coloured.

(a) The ground colour of those laid in trees and bushes is often some shade of green or blue marked with brown, red, or black, e.g. Thrushes, Finches, Crows.

(b) When the nest is placed very low down amongst herbage, or when it is placed in a covered site, the ground colour of the eggs is paler, and so are the markings, which are sometimes greenish, e.g. Redbreast, Wagtail, Whitethroat; but not so the Pipits.

(c) When exposed to some extent on the ground they are generally clay-colour, or brown, or greenish brown, spotted and blotched with a darker shade, or even with black, e.g. the Lark, Lapwing, Curlew, Gulls.

(d) Certain birds, as Ducks, Partridge, Grebes, cover their eggs when they leave the nest. Such eggs are usually white or of a pale tint. This might be expected, as the protection of colour is in such cases unnecessary.

(e) Large birds which are able to defend themselves may be expected to be capable of keeping their eggs safe from the attacks of Crows, &c. Swans and Cormorants will come under this head.

II. Birds which nest in holes nearly always have white eggs, e.g. Swift, Woodpecker, Kingfisher, Puffin, Petrel. But very small birds so nesting generally lay white eggs speckled with red.

The only exceptions which occur to me are the Wheatear, Redstart, Starling, Jackdaw, and Chough. The first two of these have already been dealt with. I have no personal knowledge of the Chough. But there is some reason to suppose that nesting in holes is a comparatively recent habit both with the Starling and the Jackdaw. In 1887 I found two Starlings' nests which were "open." One was at the top of a spruce-fir, built upon an old Wood-Pigeon's nest; the other was in ivy. Perfectly fresh-laid Starlings' eggs differ very much, varying from a decided blue to nearly white. Jackdaws sometimes lay their eggs in hollow trunks, where they can be seen from above. Moreover, I have a note to the effect that near Eyam, in 1887, some Jackdaws were nesting among the branches, after the manner of Rooks. In the 'Naturalists' Journal' (vol. vii. No. 72, June, 1898) a similar occurrence is recorded.

III. When birds build covered nests the eggs are white, spotted finely with red, black, or brown, e.g. the Wren's, Chiffchaff's, Swallow's; or pure white, e.g. the Dipper's. The House- and Tree-Sparrows are exceptions.

IV. Nocturnal birds lay white eggs, as the Short-eared Owl; or nearly white, as the Nightjar. Protective colouring is not needed in such cases, as the birds sit on their eggs throughout the day.

V. The eggs of the Accipitres are safe under the parental guardianship. They are pure white, white slightly spotted with red, or boldly blotched with red, or in some cases the ground colour is entirely hidden by the overlying red.

 

Here again the exceptions to the rule present great difficulties. Some of them are interesting enough to have attracted the attention of Dr. Wallace and Prof. Poulton.

(a) All the breeding habits of the Cuckoo are strange and abnormal. Until more is known about them we cannot hope for a satisfactory explanation of the variability of its eggs.

(b) It is a surprising fact that the Wood-Pigeon, which makes an open nest, lays pure white eggs. Dr. Wallace^[5] and Prof. Poulton^[6] give the following explanation:—They suggest that the egg is white as a protection from below; that the Wood-Pigeon builds a flimsy wicker nest, through the bottom of which the eggs can be seen; but that, being white, they are inconspicuous against the blue sky. [Dr. Wallace expresses it rather differently. After remarking that light may be seen through the nest from below, he says:—"It is a difficult matter to discover, from beneath, whether there are eggs in the nest or not, while they are well hidden by the thick foliage above."] It seems hardly possible that this is the true explanation. Wood-Pigeons' nests are not always of the wicker type; and, if it is an advantage for the eggs to be unnoticeable from below, the natural course for the birds to take would be to build solid-bottomed nests always. Nor has it yet been proved that a white egg is less conspicuous from below than a coloured one. Mr. Beddard has shown that white is not invisible from below,—that a snowflake, when seen against a blue sky, looks black. If the colours of eggs have any meaning, they are obviously a protection against marauders above the nest. It is not usual for eggs laid in open nests to be white, even when dense foliage overhangs them. The eggs being white and the nest so flimsy, it might be supposed that until recently these birds built in holes. But the fact that by far the majority of the members of this great family (Columbidæ)—which embraces some three hundred species—does not nest in holes is a very strong argument against such a theory. These birds lay but two eggs, and often begin to sit as soon as the first egg is laid. In this way the need of colour would to some extent be obviated.

(c) Lastly, we must turn our attention to the Alcidæ. The eggs of the Common Guillemot display an extraordinary variety in ground colour and markings. Dr. Wallace^[7] and Mr. Dixon^[8] suppose that this is due to their being laid on inaccessible cliffs, and thus completely protected from enemies. If this is the correct explanation, it seems strange that the eggs should be coloured at all. But a visit to Flamborough Head in the breeding season will show that these eggs are not safe from all marauders. These cliffs are tenanted by Jackdaws as well as by Guillemots. And that the former have a taste for the eggs of the latter is evident, for the shells of sucked eggs may be seen lying about on the top of the cliffs. Prof. Poulton^[9] believes that a more feasible explanation is that all this variety of colouring enables "each bird to know its own eggs." But, if this is necessary in the case of Guillemots' eggs, how do Terns and Gulls, which nest together in such dense numbers, dispense with a similar provision? Most of the eggs of any one species are very much alike, and are so difficult to see that the greatest care must be taken by anyone visiting their nesting stations in order to avoid treading on them.

The Razorbill also lays its eggs on precipitous rocks, but they are placed under cover. Though the markings vary to some extent, the ground colour is generally white, sometimes brown. The Puffin's eggs are laid far down a hole, and they are pure white. When they are fresh and clean faint traces will be found of those bold markings which are so common on the eggs of the Alcidæ. Do not these suggest that long ago the Puffin laid coloured eggs in the open, after the manner of its cousin the Guillemot at the present day?

I hope that these remarks will draw out criticisms and observations from your readers, and that thus the difficulties of the subject may to some extent be cleared up.

 

1. 'Darwinism,' p. 214.
2. Newton's 'Dictionary of Birds,' p. 101; Wallace's 'Darwinism,' pp. 217–226.
3. Newton's 'Dictionary of Birds,' p. 100.
4. 'Descent of Man,' ch. viii.
5. 'Darwinism,' p. 213.
6. 'Colours of Animals,' p. 62; cf. also Beddard's 'Animal Coloration.' p. 115.
7. 'Darwinism,' pp. 214, 215.
8. Seebohm's 'British Birds,' vol. ii. p. xxvii.
9. 'Colours of Animals,' p. 213.