BIRDS OF NORTH AND MIDDLE AMERICA 617 



least without well-defined scutella; longest primaries exceeding distal 

 secondaries by much more than one-third (sometimes by more than 

 one-half) the length of wing; second primary much longer than fourth 

 (usually longer than third), the first longer than fifth (sometimes longer 

 than third) ; tail graduated for less, to much less, than one-fifth of its 

 length; the details of the various parts of the body and plumage 

 highly variable and best described for each subgenus in order to avoid 

 many exceptions and contradictions. 



The genus is cosmopolitan in range from the high Arctic latitudes 

 to the Antipodes. It contains over 35 species with many races. 



The characters of the subgenera occurring in North and Middle 

 America are described immediately before the accounts of their in- 

 cluded forms, as they are so diverse as to make a more detailed descrip- 

 tion of the genus as a whole fuU of exceptions and contradictions and 

 to confuse rather than to clarify the picture, 



Tyjpe. — Falco subbuteo Linnaeus. 



KEY TO THE NORTH AND MIDDLE AMERICAN FORMS OF FALCO 



a. Unf Gathered part of tarsus covered with small scales, with no transverse 

 scutellae on the lower acrotarsium and no definite roT\'s of larger hexagonal 

 scales elsewhere. 



b. Inner toe, without claw, extending to or beyond the penultimate articula- 



tion of middle toe; first (outermost) primary shorter than the third; 

 second primary with inner web emarginated subterminally. 

 c. Tarsus with more than upper half densely feathered; size very large (wings 

 340-420 mm.). 

 d. The fourth primary from the outside equal to or longer than the outer- 

 most one (Bering Sea coast; south in winter). 



F. rusticolus uralensis (p. 646) 

 dd. The fourth primary from the outside less than tlie outermost one 

 (Greenland to Arctic Alaska; south in winter). 



F. rusticolus obsoletus (p. 683) 

 cc. Tarsus with less than upper half densely feathered; size smaller (wing 

 usually much less than 330 mm.). 

 d. Median pair of rectrices unbarred (w. North America from south- 

 western Canada to northwestern Mexico) . 



F. mexicanus, ad. (p. 623) 

 dd. Median pair of rectrices indistinctly barred like tlie others (w. North 

 America from southwestern Canada to northwestern Mexico). 



F. mexicanus, imm. (p. 624) 

 bb. Inner toe, without claw, falling short of penultimate articulation of middle 

 toe; first (outermost) primary much longer than the third; second primary 

 with no emargination on inner web. 



c. Tip of tail truncate or slightly emarginate; tarsus with less than one-third 



of anterior portion feathered. 

 d. Tarsus longer than middle toe without claw. 

 e. Upperparts without slate or bluish slate margins to the feathers; 

 under tail coverts marked with black (all but northwest Alexico 

 south to Argentina) F. albigularis albigularis, juv. (p. 675) 



