_Aquila_, MŒHR. 1752. (Type, _Falco chrysætos_, LINN.)
_Aëtos_, NITZSCH, 1840. (Same type.)
_Hieroaëtus_, 1844, and _Hieraëtus_, 1845, KAUP. (Type, _Falco
pennatus_, GMEL.)
_Pteroaëtus_, KAUP, 1844. (Type, _Falco vulturinus_, DAUD.)
_Uroaëtus_, KAUP, 1844. (Type, _Vultur audax_, LATH.)
_Pseudaëtus_, HODGS. 1844. (Type, _Falco bonelli_, TEMM.)
_Tolmaëtus_, BLAS. 1845. (Same type.)
_Eutolmaëtus_, BLAS. 1848. (Same type.)
[Illustration:
=41901=, ♀. ¼
=9128=, ♀. ¼
=41901=, ♀. ¼
=41901=, ♀. ¼
=54338=, ♀. ½
=12006=, ♀. ¼
=19124=, ♀ ? ¼
9128. _Haliaëtus leucocephalus._
41901 : 12006 : 19124. _Aquila chrysaëtus_, var. _canadensis_.
54338. _Archibuteo lagopus_ (tarsus from behind).]
GEN. CHAR. Form robust and structure powerful; the bearing and general
aspect that of _Buteo_ and _Archibuteo_. Wing long, the primaries long
and strong, with their emarginations very deep. Tail rather short,
slightly rounded or wedge-shaped. Bill stronger than in the preceding
genera, its outlines nearly parallel, and the tip somewhat inclined
backward at the point; commissure with a more or less prominent festoon;
nostril narrowly oval, vertical; skin of the cere very hard and firm.
Superciliary shield very prominent. Feet very strong, the membrane
between the outer and middle toes very well developed; tarsus less than
twice as long as the middle toe; outer toe equal to, or longer than, the
inner; claws very long and strong, very much graduated in size; scutellæ
of the toes small except on the terminal joint, where they form broad
transverse plates; tarsi densely feathered all round down to the base
of the toes; tibial plumes well developed, loose-webbed, their ends
reaching down to or beyond the base of the toes. Feathers of the nape
and occiput lanceolate, acute, and distinct, forming a nuchal “cape”
of differently formed feathers. Third to fifth quill longest; first
shorter than the seventh; outer five or six with their inner webs deeply
emarginated.
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.).