162 Birds of Colorado 



Key of the Families ajstj Genera. 



A. Head and neck naked (Cathartidce). Cathartes, p. 163. 



JB. Head and neck feathered. 



a. Outer toe not reversible, claws never all the same length 

 (Falconidce). 

 a^ Large ; whig over 17'0. 



a^ Tarsus feathered to the bases of the toes. Aquila, p. 181. 

 b* Tarsus feathered about half way down. Haliaeetus, p. 183. 

 b^ Smaller ; wing less than 17. 



a- Nostrils rounded, with a bony tubercle , edge of bill 

 distinctly toothed. Falco, p. 184. 



b^ Nostrils without a bony tubercle ; edge of bill never 

 toothed, though often festooned, 

 a^ Legs with the tibia always exceeding the tarsus. 



a* Only the outer two primaries emarginate on the 

 inner web. 

 a^ Tail forked to half its extent ; tarsus reticulate 

 throughout. Elanoides, p. 165. 



b^ Tail about even ; tarsus with transverse scutes in 

 front. Ictinia, p. 165. 



b* Three to five of the outer primaries emarginate. 

 a^ Face with an Owl-Uke ruif ; tarsus with scutes 

 anteriorly and posteriorly. Circus, p. 166. 



b^ Face without ruff. 



a* Tarsus half feathered, with scutes in front only. 



Buteo, p. 173. 

 b^ Tarsus feathered to the toes. Archibuteo, p. 178. 

 b' Legs with the tibia and tarsus about equal. 



a* Tarsus feathered about } ; middle toe very long, 

 without claw exceeding the outer toe with claw. 



Accipiter, p. 168. 



b* Tarsus feathered about i ; middle toe shorter, 



without claw not exceeding the outer toe with claw. 



Astur, p. 171. 



b. Outer toe reversible, claws all approximately the same length 



(Pandionidoe). Pandion, p. 192, 



Family CATHARTID^. 



Head and neck naked ; bill hooked, comparatively- 

 weak ; nostrils large, oval and completely pervious owing 

 to the absence of the inter-nasal septum ; toes long, 

 basally webbed ; claws rather weak, slight^ curved and 



