Page:The Zoologist, 4th series, vol 6 (1902).djvu/408

348 I have given the descriptions of the two species alternately, so that the various plumages may be more readily compared.

Any ornithologist looking at the series of A. gambeli when they are placed side by side in a row, with their breasts all forward, could never doubt that they all belonged to one and the same species, judging by plumage alone. Upon scrutinising the series of A. albifrons under similar conditions, it is also equally clear that they belong to one and the same species, and that those species are distinct and easily separable. Turn all the birds round and examine the outlines of the bills, and the difference will be seen to be very striking. When one's eyes become thoroughly accustomed to these outlines, it is perfectly easy to separate the species by bills alone.

I now come to a very important point. I have said that I have discovered a further valuable osteological distinction: it is that the neck in A. gambeli is about 1½ in. longer than in A. albifrons.

Up to January last I had secured all my specimens singly, and had not noticed the difference in the length of neck; but in that month I was fortunate enough to get two specimens at one time—an immature gambeli and adult albifrons, and when the two birds were lying before me I was instantly struck by the extraordinary difference in the lengths of their necks. After skinning the birds and dislocating the necks at the base of the skull, the measurements were:—Adult albifrons 7½ in., and immature gambeli 9 in. I should not have attached too much importance to this single instance, but I was enabled during February to abundantly corroborate this evidence by getting two adult gambeli which gave me necks of 8¾ in. and 9 in.; also another adult albifrons with a neck 7½ in.

I think, in the foregoing remarks, I have given abundance of proof in differences of plumage and osteological characters already well known to fully establish the distinctions between the two birds; but the final discovery ought surely to be all that is required to prove the specific validity of Anser gambeli.

It will perhaps be useful to give here, in tabular form for easy comparison, the measurements and weights of the various specimens:—