FAMILY ACCIPITRIDAE 173 



12. Under surface of body black, or blackish slate. 



Black hawk-eagle, Spizaetus tyrannus serus, p. 240 



Under surface white, barred more or less with black ; head and neck marked 



with chestnut Barred hawk-eagle, Spizaetus ornatus vicarius, p. 241 



13. Size large and robust, wing 490 mm. or more. 



Solitary eagle, Urubitornis solitaria solitaria, p. 238 

 Size smaller, wing under 450 mm 14 



14. Feathers from auricular region around forepart of head elongated to form a 



distinct facial rufif Marsh hawk, Circus cyaneus hudsonius, p. 251 



Without a facial ruff; feathers of side and forepart of head not distinctly 

 elongated IS 



15. Outer toe conspicuously shorter than inner toe; tibiotarsal joint capable of 



forward and backward flexure. 



Crane hawk, Ischnosceles caerulescens, p. 253 



Outer toe as long as, or longer, than inner toe; tibiotarsal joint capable only 



of forward flexure 16 



16. Under side of toes finely and sharply spiculate. 



Black-collared hawk, Busarellus nigricollis nigricoUis, p. 227 

 Underside of toes normal, sometimes roughened, but never sharply spicu- 

 late 17 



17. Lesser and middle wing coverts chestnut-brown 18 



l-esser and middle wing coverts not prominently chestnut-brown 20 



18. Size small, wing less than 150 mm. 



Tiny hawk, Accipiter superciliosus fontanier, immature, brown phase, p. 192 

 Size large, wing more than 300 mm 19 



19. Wings cinnamon-rufous tipped with black. 



Savanna hawk, Heterospisias meridionalis meridionalis, p. 223 

 Wings fuscous, more or less buffy white or white on inner webs. 



Harris's hawk, Parabuteo unicinctus harrisi, p. 226 



20. Breast, abdomen, and tibia white, finely and evenly barred with black. 



Barred hawk, Leucopteniis princeps, p. 222 

 Posterior under surface not as in 20 21 



21. Under surface plain dark gray, with the tibia barred with white. 



Plumbeous hawk, Leucopternis plumhea, p. 221 

 Under surface not plain gray ; tibia not barred 22 



22. Upper surface mainly pure white except for black-tipped wings and tail. 



White hawk, Leucopternis alhicollis costaricensis, p. 217 

 Upper surface with little, if any, white 23 



23. Entire under surface pure white. 



Semiplumbeous hawk, Leucopternis semiplumhea, p. 220 

 Lower surface not plain white 24 



24. Tarsus decidedly longer, more than 115 mm., so that the outstretched feet 



reach nearly to end of the tail. 



Greater black hawk, Buteogallus urubitinga, p. 229 

 Tarsus shorter, less than 100 mm 25 



25. Smaller, wing less than 350 mm 26 



Larger, wing more than 360 mm 35 



26. Very small, wing less than 150 mm. 



Tiny hawk, Accipiter superciliosus jontainier, 



adult and immature, light phase, p. 192 

 Larger, wing more than 160 mm 27 



