162 Birds of Colorado 
Key or THE FamMities AND GENERA. 
A. Head and neck naked (Cathartida). Cathartes, p. 163. 
B. Head and neck feathered. 
a. Outer toe not reversible, claws never all the same length 
(Falconide). 
al Large; wing over 17-0. 
a2 Tarsus feathered to the bases of the toes. Aquila, p. 181. 
b? Tarsus feathered about half way down. Halizetus, p. 183. 
bt Smaller; wing less than 17. 
a® Nostrils rounded, with a bony tubercle, edge of bill 
distinctly toothed. Falco, p. 184. 
b? Nostrils without « bony tubercle; edge of bill never 
toothed, though often festooned. 
a? Legs with the tibia always exceeding the tarsus. 
at Only the outer two primaries emarginate on the 
inner web. 
a5 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. 
a5 Face with an Owl-like ruff; tarsus with scutes 
anteriorly and posteriorly. Circus, p. 166. 
b> Face without ruff. 
a® Tarsus half feathored, 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. 
at Tarsus feathered about +; middle toe very long, 
without claw exceeding the outer toe with claw. 
Accipiter, p. 168. 
bt Tarsus feathered about 4; 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 
(Pandionide). Pandion, p. 192. 
Family CATHARTID&2. 
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, slightly curved and 
