_Rostrhamus_, LESS. 1831. (Type, _Falco hamatus_, ILLIG.)
GEN. CHAR. Wings and tail large, the latter emarginated. Bill very
narrow, the upper mandible much elongated and bent, the tip forming
a strong pendent hook; lower mandible drooping terminally, the gonys
straight; the upper edge arched, to correspond with the concavity of
the regular commissure. Nostril elongate-oval, horizontal. Tarsus
short, about equal to middle toe, with a continuous frontal series of
transverse scutellæ; claws extremely long and sharp, but weakly curved;
inner edge of the middle claw slightly pectinated. Third to fourth
quills longest; outer five with inner webs sinuated.
[Illustration:
=53081=, ♀. ¼
=53081=, ♀. ½
=53081=, ♀. ½
_Rostrhamus sociabilis._]
The species of this genus are two in number, and are peculiar to the
tropical portions of America, one of them being confined to the Amazon
region, the other extending to Florida in one direction and Buenos
Ayres on the other. Their nearest allies are the species _Circus_ and
_Elanus_, like them inhabiting marshy localities, where their food is
found, which consists, in large part, of small mollusca.
Species and Races.
COMMON CHARACTERS. _Adult._ Prevailing color plumbeous-black, or
bluish-plumbeous; the tail and primaries black. Entirely concolored,
or with white tail-coverts. Cere and feet orange-red. _Young._ Spotted
with blackish-brown and ochraceous, the former prevailing above, the
latter beneath.
1. =R. sociabilis.= Tail-coverts, with terminal and basal zones
of the tail, white; that of the tail more or less shaded with
grayish-brown. _Adult._ Uniform blackish-plumbeous, darker on the
head, quills, and tail. _Hab._ South America, West Indies, and
Florida.
Plumbeous of a glaucous cast, the head dark plumbeous, and
the wing-coverts lighter, inclining to grayish-brown. Wing,
13.25–15.50; tail, 6.75–8.25; bill, .85–1.04; tarsus, 1.70–2.40;
middle toe, 1.40–1.55. (2 sp. P. A. N. S.) _Hab._ Florida and West
Indies …
var. _plumbeus_.
Plumbeous of a blackish cast, the head deep black, and the
wing-coverts not lighter, and not inclining to brownish. Wing,
12.90–14.00; tail, 7.60–7.80; bill, .90–1.25; tarsus, 1.50–1.80;
middle toe, 1.45–1.65. _Hab._ South America …
var. _sociabilis_.[76]
2. =R. hamatus.=[77] Tail-coverts, with end and base of the tail,
slaty-black. _Adult._ Uniform bluish-plumbeous, darker on the
head, wings, and tail. Tail uniform black, or with two narrow,
interrupted, white bands across the middle portion (♂, Brazil, B. S.
Coll.). Wing, 11.00–12.00; tail, 5.00–7.00; bill, 1.02–1.07; tarsus,
1.75–1.90; middle toe, 1.45. _Hab._ Amazon region of South America.
Rostrhamus sociabilis, var. plumbeus, RIDGWAY.