_Accipiter_, BRISS. 1760. (Type, _Falco nisus_, LINN.)
_Nisus_, CUV. 1799. (Same type.)
_Astur_, LACÉP. 1801. (Type, _Falco palumbarius_, LINN.)
_Dædalion_, SAVIG. 1809. (Same type.)
_Dædalium_, AGASS. (Same type.)
_Sparvius_, VIEILL. 1816. (Same type.)
_Jerax_, LEACH, 1816. (Same type.)
_Aster_, SWAINS. 1837. (Same type.)
_Micronisus_, GRAY, 1840. (Type, _Falco gabar_, DAUD.)
_Phabotypus_, GLOG. 1842. (Same type.)
_Hieraspiza_, 1844, _Jeraspiza_, 1851, and _Teraspiza_, 1867, KAUP.
(Type, _Falco tinus_, LATHAM.)
_Hieracospiza_, AGAS. (Same type.)
_Nisastur_, BLAS. 1844. (Same type.)
_Urospiza_, 1845, _Urospizia_, 1848, and _Uraspiza_, 1867, KAUP.
(Type, _Sparvius cirrhocephalus_, VIEILL.)
_Leucospiza_, KAUP, 1851. (Type, _Falco novæ-hollandiæ_, GMEL.)
_Cooperastur_, BONAP. 1854. (Type, _Accipiter cooperi_, BONAP.)
_Erythrospiza_, KAUP, 1867. (Type, _A. trinotatus_ TEMM.? not of
BONAP. 1830!)
GEN. CHAR. Form slender, the tail long, the wings short and rounded,
the feet slender, the head small, and bill rather weak. Bill nearly as
high through the base as the length of the chord of the culmen, its
upper outline greatly ascending basally; commissure with a prominent
festoon. Superciliary shield very prominent. Nostril broadly ovate,
obliquely horizontal. Tarsus longer than the middle toe, the frontal
and posterior series of regular transverse scutellæ very distinct,
and continuous, sometimes fused into a continuous plate (as in the
_Turdinæ_!). Outer toe longer than the inner; claws strongly curved,
very acute. Wing short, much rounded, very concave beneath; third to
fifth quills longest; first usually shortest, never longer than the
sixth; outer three to five with inner webs cut (usually sinuated). Tail
long, nearly equal to wing, usually rounded, sometimes even, more rarely
graduated (_Astur macrourus_) or emarginated (some species of subgenus
_Nisus_).
Subgenera.
Less than one third of the upper portion of the tarsus feathered in
front, the feathering widely separated behind; frontal transverse
scutellæ of the tarsus and toes uninterrupted in the neighborhood of
the digito-tarsal joint, but continuous from knees to claws. Tarsal
scutellæ sometimes fused into a continuous plate …
_Nisus._
More than one third (about one half) of the upper portion of the
tarsus feathered in front, the feathering scarcely separated behind;
frontal transverse scutellæ of the tarsus and toes interrupted in the
region of the digito-tarsal joint, where replaced by irregular small
scales. Tarsal scutellæ never fused …
_Astur._
The species of this genus are exceedingly numerous, about fifty-seven
being the number of nominal “species” recognized at the present date.
Among so many species, there is, of course, a great range of variation
in the details of form, so that many generic and subgeneric names have
been proposed and adopted to cover the several groups of species which
agree in certain peculiarities of external structure. That too many
genera and subgenera have been recognized is my final conclusion, after
critically examining and comparing forty of the fifty-seven species of
Gray’s catalogue (Hand List of Birds, I, 1869, pp. 29–35). The variation
of almost every character ranges between great extremes; but when all
the species are compared, it is found that, taking each character
separately, they do not all correspond, and cross and re-cross each
other in the series in such a manner that it is almost impossible to
arrange the species into well-defined groups. From this genus I exclude
_Lophospiza_, Kaup (type, _L. trivirgatus_); _Asturina_, Vieill. (type,
_A. nitida_); _Rupornis_, Kaup (type, _R. magnirostris_); _Buteola_,
Dubus (= _Buteo_, type, _B. brachyura_, Vieill.); included by Gray under
_Astur_, as subgenera, and _Tachyspiza_, Kaup (type, _T. soloensis_);
and _Scelospiza_, Kaup (type, _S. francesii_); which are given by
Gray as subgenera of _Micronisus_, Gray (type, _Accipiter gabar_),
the species of the typical subgenus of which, as arranged in Gray’s
Hand List, I refer to _Nisus_. All these excluded names I consider as
representing distinct genera.
The species of this genus are noted for their very predatory
disposition, exceeding the Falcons in their daring, and in the quickness
of their assault upon their prey, which consists chiefly of small birds.