This genus is almost peculiar to the Old World, where about seventeen so-called species are known, while America has no member of the genus exclusively its own, the single North American species being the same as the European one. Though the details of external structure vary somewhat, and the size ranges from that of a Buteo to that of a sea-eagle (Haliaëtus), the generic characters given in the above diagnosis apply well to all the species. The species of Heteropus, Hodgson, 1842 (A. malayensis, Rein. and H. gurneyi, Gray), I remove entirely from Aquila, since they differ so strikingly in many important respects. With the general aspect of Aquila, Heteropus has the outer toe disproportionately shorter than the inner (instead of equal to it, or longer), which curious feature it shares only with Geranospiza of tropical America, and Polyboroides of South Africa,—both terrestrial Buteonine forms of specialized structure. An entirely peculiar feature of Heteropus is the great length and straightness of the claws. Its bill is more like that of Archibuteo than like that of Aquila.
The North American and European races of the single species which occurs on the former continent may be distinguished as follows:—
Species and Races.
A. chrysaëtus. Wing, 23.00–27.00; tail, 14.00–16.00; culmen, 1.50–1.90; tarsus, 3.40–4.20; middle toe, 2.40–3.10. Third to fifth quill longest first shorter than seventh or eighth. Color blackish-brown, or umber-brown, nearly uniform, except on the tail; nuchal cape of lanceolate feathers, and tarsi of a paler and more tawny tint. Adult. Tail transversely clouded with ashy, and not white at the base; feathers of the body not distinctly white beneath the surface. Young. Tail with the basal half plain white, the terminal portion plain blackish; feathers of the body distinctly white beneath the surface. Hab. Nearctic and Palæarctic Realms.
Tarsi of adult pale umber; of young, dirty whitish. Hab. Palæarctic Realm … var. chrysaëtus.[92]
Tarsi of adult deep umber; of young light brown. Hab. Nearctic Realm … var. canadensis.
Aquila chrysaëtus, var. canadensis (Linn.).
GOLDEN EAGLE; RING-TAILED EAGLE.
Aquila chrysaëtus (not of Linn.!)
, Rich. & Sw. F. B. A. II, 1831, 12.—Jard. (Wils.) Am. Orn. II, 1832, 304.—Bonap. List, 1838, 2.—Aud. Synop. 1839, 9.—De Kay, Zoöl. N. Y. II, 4, pl. vi, f. 14 (Juv.).—Cass. B. Cal. & Tex. 109.—Strickl. Orn. Syn. I, 55 (in part).—Brewer, Oölogy, 1857, 45.—Coues, Key, 1872, 219. Falco chrysaëtus, (Linn.) Max. Cab. J. 1858, VI, 9.—Blas. Ber. XVI, Vers. Deutsch. Orn. 1862, 83 (“absolutely identical with European”). Falco canadensis, Linn. S. N. (ed. 10), 1766, 88. Aquila canadensis, Wils. Am. Orn. 1808, pl. lv, f. 1.—Heerm. P. R. R. Rept. II, 1855, 30.—Cass. Birds N. Am. 1858, 41.—Coues, P. A. N. S. 1866, 13.—Gray, Hand List, I, 40. Falco niger, Gmel. S. N. 359. Aquila nobilis, Pall. Zoög. Ros. As. 1811. Aquila fulva (not of Linn.!)