BIRDS OF NORTH AND MIDDLE AMERICA 579 



>Polyborinae Bonaparte, Consp. Gen. Av., i, 1850, 12 (includes Polyboroides). 



= Polyborinae Carus, Handb. Zool., i, 1868-75, 306.— Oberholser, Outl. 



' Classif. North Amer. Birds, 1905, 2.— Peters, Check-list Birds of World, 



i, 1931, 278. 

 = Pseudo-Vulturidae Lesson, ficho du Monde Savant, 9« ann., vi, ser. 2, No. 49, 



Dec. 25, 1842, col. 1151. 

 = Polybori Ridgway, Proc. Boston Soc. Nat. Hist., xvi, 1873, 50; U. S. Geol. 



and Geogr. Surv. Terr., ser. 2, Bull. 4, 1875, 4, 5, 6, 7; No. 6, 1876, 452. 

 = Polyboreae Ridgwat, Orn. Illinois, i, 1889, 427. 



Ignoble Falcoiies of more or less vulturine habits; the more typical 

 forms largely terrestrial and ambulatorial, therefore with relatively 

 long legs and short toes; all (?) with a naked or downy crop, visible 

 externally when extended with food, and, except genus Milvago, with 

 head partly bare. 



Maxillary tomium without a distinct, if any, subterminal "tooth" 

 and mandibular tomium without distinct notch; ^^ superciliary proc- 

 ess of lachrymal short, extending not more than halfway across orbit; 

 posterior margin of metasternum deeply indented by a pair of notches 

 (these double in Milvago); three or more outer primaries with inner 

 webs sinuated at about (on outermost anterior to) middle portion. 



Sexes alike in coloration, but young very different from adults. 



Nidification as in Falconinae, the eggs very sunilar, both in form 

 and coloration. 



The Polyborinae are vulturelike Falcones, whose distinctive char- 

 acters are far more superficial than would be imagined from an ex- 

 amination of their external structure alone. Their chief characters 

 are, in fact, teleological or adaptive, and their relationship to the 

 true falcons therefore of much the same nature, if not in the same 

 degree, as that of the Old World vultures to the buzzards (Bute- 

 oninae). Although far from numerous in species, the Polyborinae 

 present great differences of external aspect, the extremes being repre- 

 sented by the long-legged, ambulatorial, largely terrestrial and essen- 

 tially necrophagous caracaras (genus Polyborus) w^hose bearing when 

 standing or moving on the ground strongly suggests that of the secre- 

 tary bird (Sagittarius serpentarius) and the short-legged, insessorial, 

 arboreal, and insectivorous Daptrius. These are the two most spe- 

 cialized types, the more generalized genus Milvago presenting a very 

 close approach to the true falcons, through a New Zealand genus of 

 the latter subfamily {leracidea) . 



The Polyborinae are peculiar to America and are most numerous 

 m South America, only four of the ten known species being found 

 north as far as Panama; and of these, one (Milvago chimachima) finds 



"8 Though faint indications of these are observable in some genera {Milvago and 

 Phalcobaenus) in the horny sheath, they cannot be detected in the bones of the 

 bill. 



839094—50 38 



