_Circus_, LACÉP. 1800, 1801. (Type, _Falco æruginosus_, LINN.)
_Pygargus_, KOCH, 1816. (Same type.)
_Strigiceps_, BONAP. 1831. (Type, _Falco cyaneus_, LINN.)
_Glaucopteryx_, KAUP, 1844. (Type, _Falco cineraceus_, MONT.)
_Spilocircus_, KAUP, 1847. (Type, _Circus jardini_, GOULD.)
_Pterocircus_, KAUP, 1851. (Same type.)
_Spizacircus_ and _Spiziacircus_, KAUP, 1844 and 1851. (Type, _Circus
macropterus_, VIEILL.)
[Illustration:
=1042=, ♀. ½
½
¼
_Circus hudsonius._]
GEN. CHAR. Form very slender, the wings and tail very long, the head
small, bill weak, and feet slender. Face surrounded by a ruff of stiff,
compact feathers, as in the Owls (nearly obsolete in some species). Bill
weak, much compressed; the upper outline of the cere greatly ascending
basally, and arched posteriorly, the commissure with a faint lobe;
nostril oval, horizontal. Loral bristles fine and elongated, curving
upwards, their ends reaching above the top of the cere. Superciliary
shield small, but prominent. Tarsus more than twice the middle toe,
slender, and with perfect frontal and posterior continuous series of
regular transverse scutellæ; toes slender, the outer longer than the
inner; claws strongly curved, very acute. Wings very long, the third or
fourth quills longest; first shorter than the sixth; outer three to five
with inner webs sinuated. Tail very long, about two thirds the wing;
rounded.
The relationships of this well-marked genus are, to _Accipiter_ on the
one hand, and _Elanus_ on the other; nearest the former, though it is
not very intimately allied to either. I cannot admit the subgenera
proposed by various authors (see synonomy above), as I consider
the characters upon which they are based to be merely of specific
importance, scarcely two species being exactly alike in the minute
details of their form.
The species are quite numerous, numbering about twenty, of which only
about four (including the climatic sub-species, or geographical races)
are American. North America possesses but one (_C. hudsonius_, Linn.),
and this, with the _C. cinereus_, Vieill., of South America, I consider
to be a geographical race of _C. cyaneus_ of Europe.
The birds of this genus frequent open, generally marshy, localities,
where they course over the meadows, moors, or marshes, with a steady,
gliding flight, seldom flapping, in pursuit of their food, which
consists mainly of mice, small birds, and reptiles. Their assault upon
the latter is sudden and determined, like the “Swift Hawks,” or the
species of _Accipiter_.
In the following synopsis, I include only the three forms of _C.
cyaneus_, giving the characters of the European race along with those of
the two American ones.
Species and Races.
=C. cyaneus.= Wing, 12.50–16.00; tail, 9.00–10.70; culmen, .60–.80;
tarsus, 2.42–3.25; middle toe, 1.10–1.55. Third to fourth quills
longest; first shorter than sixth or seventh; outer four with inner
webs sinuated. _Adult male._[78] Above pearly-ash, with a bluish cast
in some parts; breast similar; beneath white, with or without rufous
markings. _Adult female._ Above brown, variegated with ochraceous
on the scapulars and wing-coverts; beneath yellowish-white or pale
ochraceous, with a few longitudinal stripes of brown. _Young_ (of both
sexes). Like the adult female, but darker brown above, the spotting
deeper ochraceous, or rufous; beneath pale rufous, the stripes less
distinct.
Tail and secondaries without a subterminal band of dusky; lower
parts without any markings.
Wing, 12.50–15.00; tail, 9.00–10.70; culmen, .60–.75; tarsus,
2.70–2.85; middle toe, 1.10–1.35. _Hab._ Europe …
var. _cyaneus_.[79]
Tail and secondaries with a subterminal band of dusky; lower parts
with rufous markings.
Wing, 12.90–16.00; tail, 9.00–10.50; culmen, .65–.75; tarsus,
2.90–3.25; middle toe, 1.20–1.55. Lower parts with scattered
irregular specks, or small cordate spots, of reddish-rufous.
_Hab._ North and Middle America …
var. _hudsonius_.
Wing, 12.40–14.50; tail, 8.50–10.50; culmen, .62–.81; tarsus,
2.42–3.00; middle toe, 1.20–1.50. Lower parts with numerous
regular transverse bars of reddish-rufous _Hab._ South America …
var. _cinereus_.[80]
Circus cyaneus, var. hudsonius (LINN.).