The species of this subgenus are generally of small size and slender form; but with a graceful and apparently delicate structure they combine remarkable strength and unsurpassed daring. They differ from the species of Astur mainly in less robust organization. The species are very numerous, and most plentiful within the tropical regions. The Old World possesses about thirty, and America about fifteen, nominal species. Several South American species are intimately related to the two North American ones, and may prove to be only climatic races of the same species; thus, erythrocnemis, Gray (Hand List, p. 32, No. 305) may be the intertropical form of fuscus, and chilensis, Ph. and Landb. (Hand List, No. 314), that of cooperi. But the material at my command is too meagre to decide this.
26588, ♀. ¼
Nisus cooperi.
26588, ♀. ¼
Nisus cooperi.
10759, ♂. ½
Nisus fuscus.