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.