The cry of the Winter Hawk is clear and prolonged, and resembles the syllables kay-o. After uttering these notes, it generally alights. Towards spring they associate in small parties of four or five, to perform their migrations. In this respect the species resembles most of the Marsh Hawks or Hen-harriers.
Falco hyemalis, Gmel. Syst. Nat. vol. i. p. 274.—Lath. Ind. Ornith. vol. i. p. 34.—Ch. Bonaparte, Synops. of Birds of the United States, p. 33.
Winter Falcon, Falco hyemalis, Wils. Amer. Ornith. vol. iv. p. 73. Pl. 35.
Adult Male. Plate LXXI.
Bill short, as broad as deep at the base, the sides convex, the dorsal outline convex from the base; upper mandible cerate, the edges blunt, slightly inflected, with an obtuse lobe towards the curvature, the tip trigonal, deflected, very acute; lower mandible involute at the edges, a little truncate at the end. Nostrils round, lateral, with a soft papilla in the centre. Head rather large, neck and body rather slender. Tarsus rather slender, anteriorly scutellate; toes scutellate above, scaly on the sides, scabrous and tuberculate beneath; middle and outer toe connected at the base by a small membrane; claws roundish, curved, slender, very acute.
Plumage compact, imbricated; feathers of the head and neck narrow towards the tips, of the back broad and rounded; tibial feathers elongated behind. Wings long, third and fourth primaries longest, the first short.
Bill light blue, darker at the tip; cere, basal margin of the bill, edges of the eyelids, and the feet, yellow, tinged with green. Iris yellow. Claws black. Head, neck and back, pale brownish-red, longitudinally spotted with dark-brown, the sides and fore-part of the head greyish-white. Upper tail-coverts bluish-grey at the margins. Tail dull brown, banded with brownish-white, and tipped with white. Lesser wing-coverts brownish-red, spotted with dark brown; larger coverts and secondary quills umber, banded with brownish-white; primary quills light yellowish-red at the base, dull brown towards the end, barred with dark brown. Lower part of the neck, the sides and under wing-coverts, light brownish-red, the former longitudinally lined with brown. Breast greyish-white, sparsely marked with guttiform spots, abdomen white. Tibial feathers yellowish-white, marked with small roundish spots.
Length 22 inches; bill along the back 1½; tarsus 3.
Compared with the adult male of the Red-shouldered Hawk, the present bird is much larger, and differs greatly in colouring; but the differences will be best understood by referring to the figures.