have beside me specimens in which the colour of the plumage is very dif-
ferent, some being quite light, others almost black ; and I feel pretty con-
fident that further researches i-especting this species will shew that my
opinion is not incorrect, when I say that the Rough-legged Falcon of
America and the F.alco niger of Wilson, are the same bird.
I am of opinion that the reason for which the dark coloured indivi- duals are of much rarer occurrence with us, than the lighter ones, is, that the former being older and stronger birds, are much better able to bear the inclemency of the weather in more northern regions.
Falco lagopus, Gmel. Syst. Nat. vol. i. p. 260 — Lath. Ind. Ornith. voL i. p. 19 — Ch. Bonaparte, Syiiops. of Birds of the United States, p. 32.
BuTEO LAGOPUS, Sivains. and Richards. Fauna Bor. Amer. part ii. p. 52.
KouGH-LEGGED Falcon, Falco lagopus, Wils. Amer. Ornith. vol. iv. p, 59. pi. 33.
Fig. 1 Nuttall, Manual, part i. p. 97.
Middle-aged Male. Plate CLXVL
Bill short, as broad as deep at the base, which is cerate, the sides con- vex ; upper mandible with the dorsal outline straight and declinate at the base, soon becoming convex, the tip trigonal, descending obhquely, acute, the sharp margin undulated and perpendicular ; lower mandible with the back convex, the edges sharp, arched, and inflected, the tip obliquely truncate. Nostrils large, subovate in the fore and imder part of the cere. Head rather large, broad, neck of moderate length, body robust. Feet short, robust ; tarsi roundish, feathered ; toes short, and rather small, hind toe and inner strongest and nearly equal, the latter connected with the middle at the base by a short membrane, the outer smallest ; aU with four transverse scutella at the end, the rest of their upper parts covered with very small hexagonal scales ; claws compressed, strong, curved, acute, flat beneath.
Plumage ordinary, soft beneath. Space between the bill and eye co- vered with bristly feathers, the bases of which are furnished with short barbs. Feathers of the head and neck lanceolate, of the back and breast broad and rounded, of the legs short and narrow, excepting the external tibial, which are long and rounded. Wings long, third quill longest, fourth almost equal, second shorter than fifth, first very short ; first four abruptly cut out towards the end on the inner web ; secondaries broad and rounded. Tail rather long, broad, rounded.
Bill dull bluish-grey, black at the end. Iris hazel, projecting part
