A History of North American Birds; Land Birds; Vol. 1 of 3

by Spencer Fullerton Baird; T. M. Brewer; Robert Ridgway

Ægiothus linarius.
39364 ♂

Sp. Char. Bill very short, conical, acutely pointed, the outlines sometimes concave; the commissure straight; the base of the upper mandible and the nostrils concealed by stiff, appressed bristly feathers; middle of the mandible having several ridges parallel with the culmen. Inner lateral toe rather the longer, its claw reaching the middle of the middle claw; the hind toe rather longer, its claw longer than the digital portion. Wings very long, reaching the middle of the tail; second quill a little longer than the first and third. Tail deeply forked.

Ægiothus linarius.

Difficult as it sometimes is to define with precision the characters of closely allied species of birds, there are few genera where this is the case more strikingly than in Ægiothus. Leaving out of view the peculiar European species, it has been a mooted question whether North America, including Greenland, possesses one, two, or six species, owing to the strictly boreal distribution of these birds, and the fact that their summer resorts are seldom invaded by the naturalist. The necessary means of determining the proper distribution of the forms and the variations with season, locality, and sex, are scarcely to be met with in any public museum, that of the Smithsonian Institution, however, being the most complete in this respect.

To Dr. Coues, as quoted above, we owe the most satisfactory indications of the different species and varieties, his papers in the Proceedings of the Philadelphia Academy of Natural Sciences

(1861, 375; 1863, 40; and 1869, 180) being models of ornithological criticism and discussion. His labors have enabled us to define with precision the various forms, both European and American, found in the genus, and have brought us to satisfactory conclusions in reference to their limitations.

Mr. Ridgway has lately made a careful revision of the specimens of Ægiothus in the Smithsonian collection, and with a general concurrence in the conclusions of Dr. Coues in regard to the differences observable, he suggests, as an application of the laws more recently verified by him and myself in our examination of the North American land-birds, that we may best consider the actual species to be two in number, namely, canescens and linarius, ranging the other forms under these, either as geographical races or as seasonal stages. Bearing in mind the general law that the more boreal or Greenland-born specimens should be larger than the more southern or Continental, and that the peculiar dark plumage of fuscescens and rostratus only occurs in summer breeding specimens, he considers these as identical with linarius and holbölli; the winter plumages respectively of the same two races of one species, linarius; the latter race, holbölli, being the larger or Greenland form. If fuscescens be darker than summer linarius from Europe, it is simply another instance of the darker tints of Arctic American birds as compared with European.

Ægiothus canescens and exilipes Mr. Ridgway considers as the Greenland (larger) and Continental (smaller) races of one species, which perhaps do not differ so much with season as do those of linarius. The differences in the size and proportions of bill, and perhaps of feet, Mr. Ridgway does not think of much importance, as great variations are observable in this respect in specimens from the same locality, and the actual differences of the bill are obscured by the greater length of the bristly feathers around its base in winter, making it appear considerably shorter. Indeed, Professor Alfred Newton maintains that the same bird will have the bill considerably longer in summer, after living on soft insect food, and shorter in winter when worn down by use on hard seeds. Mr. Ridgway finds, too, that specimens of linarius from Kodiak differ in a much longer and more slender bill than usual, in this respect resembling Alaska specimens of several other Fringillidæ.

The following synopsis expresses Mr. Ridgway’s views as indicated above: a critical examination of a series of more than two hundred specimens, in the collection of the Smithsonian Institution, being the basis of his conclusions.—S. F. B.