The Bird Watcher in the Shetlands, with Some Notes on Seals—and Digressions

by Edmund Selous

(11) A bird that, from the dark crown to the dark wing-tips, is, above and below, a uniform light fawny dun.

(12) A bird that would be the extreme light form (No. 1) that I have first described, were it not that, both on the throat and breast, the cream is encroached upon by cloudy barrings of a soft greyey-brown (or something between the two) which extend also over the under surface of the wings. Moreover, a toning of the darker colour of the general upper surface encroaches a little upon the cream of the nape.

(13) A bird exhibiting the uniform, dusky-dunnish colour of the common form (a shade lighter, perhaps, on the under surface), but with a cream patch on each side of the neck, just below the head. These patches are not, perhaps, of the brightest cream, but they are very conspicuous, whether the bird is seen standing or flying—in fact, the salient feature.

(14) A bird that would be the extreme light form (No. 1), but for a distinct collar of soft brown dividing the cream of the neck and throat from that of the breast.

(15) A bird that is yellowish dun on the neck and throat, mottled-brown on the breast, and a fine cream on the ventral surface.

Moreover, all these birds differed to a greater or less extent in those lighter markings of the quill feathers, both on the upper and under surface, some being lighter and some darker; following, in this respect, the general colouring. This feature, however, is only apparent when the birds fly, and I found it too laborious to include.

I can say with certainty, I think—judging by the lance-like projecting feathers of the tail, absent in the young bird, and by every other indication—that all the individuals here described by me, were birds of mature plumage. They were all established in one locality, and I was able to compare most of them with each other. I think, therefore, that though there might, perhaps, be some difference of opinion in regard to some of my colour terms—as where would there not be?—yet that the variation between the different forms is properly brought out. Without my seeking it, the list includes the two extreme forms, as I believe them to be, of dark and light; the former represented by a uniformly dark-brown bird, the latter by one having the whole under surface of the body, as well as the sides and nape of the neck, of a beautiful cream colour, by virtue of which, and of the salient contrast exhibited between this and the dusky upper surface, it is extremely handsome, not to say beautiful—one of the handsomest of all our birds in my opinion. Both the extreme forms are uncommon, but only, I think, as compared with all the intermediate shades, not with any one of them. Also the extreme light, or handsome, form seems to me to be commoner than the extreme plain one. Should not a bird like this be described as multi-morphic rather than as dimorphic? I believe that there exists as perfect a series between the two extreme forms as between the least eye-like and the most perfect eye-feather in the tail of the peacock—to take the well-known illustration given by Darwin to enforce his arguments in favour of sexual selection. The eye, however, insensibly masses the less saliently distinguished individuals together, so that those in whose plumage the light colour is more en évidence than the dark, go down as the light form, and vice versâ. Moreover, the more prononcé a bird is, in one or another direction, the more it is remarked; so that, perhaps, the intermediate shadings are forgotten, on the same principle as that by which extreme characters, in any direction, are more appreciated than less extreme ones, by the breeders of fancy birds—pigeons, poultry, etc. The uniform brown form, however, as being less striking (though extreme at one end) is not, I believe, so much noticed as those various dunnish shades, which have, in my view, been classed all together, as the dark variety.

In regard to the young birds, I only remember those nestling ones which had feathers under the fluff, as brown, without any admixture of cream. But I had not, at that time, these matters in my mind, and, moreover, I did not see many. When older, however, and able to fly, all that I have seen have had a distinct colouring of their own—for their plumage has borne a considerable resemblance to that of the Great Skua (Stercorarius catarriactes), being mottled on the back with two shades of brown, a darker and a lighter one. I got the effect of this when I watched young birds flying or standing, and one day I caught one whose wing had been injured, and saw that it was so. This resemblance is increased by such birds wanting the two lance-like feathers in the tail. As I say, this mottled brown is the only kind of colouring which I have seen in these immature but comparatively advanced birds, and my impression is that, in the still younger birds, such mottling was either absent or not so noticeable. At any rate, I have no clear recollection of it.

My own explanation of all these facts is that Stercorarius crepidatus—by my faith, 'tis a pretty name, though not wholly deserved—having been, originally, a plain homely-coloured bird, like his relative, the great skua, is being gradually modified, under the influence of sexual selection, into a most beautiful one, as represented by the extreme light or half-cream form. Natural selection, in the more general sense, seems here excluded, or, at any rate, extremely doubtful; and if it be suggested that the lighter birds have the more vigorous constitutions, that they are fuller of verve and energy, to which they owe their cream colouring, I, for my part, can only say "Prodigious!" (or think it), like Dominie Sampson. But I can assure all those who hold this unmanageable view—for really there is no dealing with it—that the one sort came not a whit nearer to knocking my cap off than did the other. But, leaving shadows, the main facts here suggest choice in a certain direction. There is a gradation of colour and pattern, connecting two forms—one plain, the other lovely. This suggests a passage from one to the other, and if the plain mature form—I mean the uniform brown one—most resembles the young bird in colouring—which to me it seems to do—whilst the young bird resembles, more than any old one, an allied plainer species, this makes it more than likely that the passage has been from the plain to the lovely, and not from the lovely to the plain. Supporting and emphasising this, we have the absence, in the tail of the young bird, of those lance-like feathers which give so marked a character to, and add so infinitely to the grace of, the old one. Of what use can this thin projection, an inch or so beyond the serviceable fan of the tail, be to the bird? Seeing how well every other bird does without it, can we suppose it to be of any service? Its beauty, however—which one misses dreadfully in the young flying bird—is apparent to any one, and it goes hand in hand with an ascending scale of beauty in colour. All this seems to me to point strongly towards sexual selection as the agency by which these changes have been, and are being, effected;[1] since I am, personally, a believer in the reality of that power, having never heard or read anything against it, so convincing to my mind as what Darwin said for it, nor seen anything that has appeared to me to be inconsistent either with his facts or his arguments.

[1] It is a strong enforcement, I think, of this view, that in another variable species of skua—Stercorarius pomatorhinus—the same two feathers give the bird "the grotesque appearance of having a disk attached to its tail."