Page:The Zoologist, 4th series, vol 6 (1902).djvu/399

Rh connecting links later, and probably next season. One reason why my series of A. gambeli is so much more perfect than that of A. albifrons arises from the fact that, out of the great numbers of White-fronted Geese which have come under my notice, I have been in the habit, fortunately, of selecting only striking-looking birds, leaving the ordinary run to be secured at any time.

I shall now endeavour to show that these large-billed, heavily barred, or striking-looking immature birds should all be regarded as specimens of A. gambeli.

This series of ten specimens is a singularly, and I may say valuably complete one, ranging from the first plumage, through almost every grade, up to the breeding bird with glossy black under parts.

Now, it is in the two extremes—the immature and breeding stages—that it is most easy to discriminate between the two species, so far as plumage goes; in the intermediate or winter stage it is more difficult, as the student has then to rely mainly upon the differences in the size of the bill, a slightly longer tarsus, and, as my series shows, the distinctly lighter colour of the extreme outer wing coverts; this latter runs practically through the whole series, but perhaps too much importance must not be attached to it. There is another, and I consider very important osteological character, which I have discovered, and which cannot be detected unless the bird is in the flesh, but this I shall refer to in its proper place.

I believe that this similarity in the winter plumages of the two species—the stage most readily procurable by collectors—and the fact that there is no full, or in any way complete description published of the immature, or breeding stages, has led to much confusion, and caused the bird not only to be overlooked as a British species, but its specific validity to be doubted.

Because large-billed specimens have been procured in Great Britain, it has been concluded that they must belong to A. albifrons, and therefore that this bird has sometimes a bill quite as large as A. gambeli. If those British-killed, large-billed specimens in various collections were admitted, as they should, to be A. gambeli, much confusion would have been avoided.

My series demonstrates clearly the very important fact that the immature conditions of the plumage in A. gambeli are quite 2 2