The above arrangement may appear satisfactory to the casual observer, but the trouble with it is that all of the above characters, particularly those on which Dr. Dwight bases his new species, are decidedly variable and inconstant. Size is the most satisfactory character but even this shows intergradation or overlapping and greater individual variation in each group than the differences in averages between the groups. The measurements, in inches, of the four forms, which I have taken or had sent to me, are as follows:—
The other characters are equally confusing. The nape is lightest and almost constantly so in North American pacifica; it is darkest in viridigularis and more or less intermediate in many specimens of the other two forms.
The black throat patch terminates below in a straight line almost invariably in North American pacifica; I have seen but one exception to this rule; but in Siberian pacifica this character is less constant. In viridigularis this patch terminates below in a decided point, in all specimens that I have seen. In European arctica about half of the specimens I have seen have the patch decidedly pointed below and the others have it nearly straight or only slightly pointed.
The colored reflections of the black throat-patch are the most variable and inconstant of all the characters. In viridigularis three of the specimens examined show mainly greenish colors but even these show some signs of purple; and in one, a bird in my own collection, the colors are about equally divided. In European arctica about half of the specimens show mainly purplish reflections, while fully half show both purplish and greenish. In North American pacifica the purplish reflections predominate, but five specimens out of twenty-two show more or less greenish in certain lights. Mr. Waldron DeWitt Miller, in sending me descriptions of Pacific Loons in the American Museum, used the following terms in designating the colors of the throats; greenish-blue, bluish-green, dark greenish-blue, violaceous and dark violet. It can be easily seen from the above that the colors are very variable.
Dr. Dwight says, in his diagnosis of viridigularis:—“The green coloration of the throat is the essential character that sets this species apart from arctica and its races, which all have purple throats.” In the light of the facts stated above this “essential character” disappears and his new species must be reduced to the rank of a subspecies at least. Even a subspecies must prove to be fairly constant in a more or less definite range. The range of viridigularis is very imperfectly known; the four specimens, referable to this form, that I have seen were taken at Nijni Kolymsk, Siberia, St. George Island, Bering Sea, Nome and Saint Michael, Alaska; Dr. Dwight’s specimens all came from northeastern Siberia. The Nijni Kolymsk bird, referred to above, is somewhat intermediate between viridigularis and arctica; if it had been taken in Europe it would probably be referred to the latter. I also have a perfectly typical pacifica from the Kolyma River, Siberia.
I have seen birds from Victoria, B. C., from Finland and from Norway which closely approach this new form, viridigularis, in size and color characters. If we had a larger series of arctica from Europe and Asia available for comparison, we could perhaps match these birds exactly and we could certainly show, if I have not already demonstrated it, that viridigularis is merely a subspecies of arctica. To use Dr. Dwight’s own terms, the green throat seems to be a quantitative rather than a qualitative character.