90 BULLETIN- 86, UNITED STATES NATIONAL MUSEUM. 



Chordeiles acutipennis exilis is much more like the widely separated 

 Yucatan form, Chordeiles acutipenms micromeHs^ than like the 

 intervening and undoubtedly close ally, Chordeiles acutipennis acuti- 

 pennis. Other than this, the geographical variations of this species 

 present no peculiarities. 



The five forms here treated under Chordeiles acutipenms are un- 

 doubtedly all subspecies, and the three heretofore recognized currently 

 pass as such. The Peruvian Chordeiles acutipennis exilis doubtless 

 intergrades geographically with Chordeiles acutipenms acutipennis., 

 though we have seen no actual intermediates. Although Chordeiles 

 acutipenms micromeris ^ has in the breeding season no geographical 

 connection with Chordeiles a. acutipenms^ its individual variation in 

 both size and color bridges the gap between the characters of these 

 two forms ; while the same is practically true of Chordeiles acutipen- 

 nis micromeris'^ and the much more widely separated Chordeiles 

 acutipennis exilis. The northern Chordeiles acutipennis texensis 

 passes into Chordeiles acutipennis micromeris'^ in southern Mexico, 

 intergrading both geographically and individually; and similarly 

 into Chordeiles acutipennis inferior^ in southern California and ex- 

 treme northern Lower California. Actual geographical intermedi- 

 ates are, however, few in the material examined, doubtless from 

 lack of specimens from the particular localities where intergradation 

 takes place; but intermediates due to individual variation are of 

 frequent occurrence. 



The characters which serve to separate the several subspecies con- 

 sist largely in differences of size, principally of wing and tail, some- 

 times also of exposed culmen, tarsus, and middle toe ; the colors and 

 general tone of upper surface and lower parts, light or dark; the 

 width of both the dark bars and the light interspaces on the posterior 

 lower surface ; and the width of the light bars on the tail. 



Geographical distribution. — The breeding range of Chordeiles 

 acutipennis as a species extends, in South America, from southern 

 Brazil to Venezuela and Colombia, including, as well, the islands of 

 Tobago and Margarita ; also to British Honduras, Guatemala, Mexico, 

 and the southwestern portion of the United States. It winters also 

 in the remaining countries of Central America. The typical race, 

 Chordeiles acutipennis acutipennis^ occupies an area in South America 

 approximately twice as great as the combined range of the four other 

 subspecies. Of the latter, Chordeiles acutipennis texensis has a range 

 of considerable extent ; but Chordeiles acutipennis exilis and Chor- 



1 See p. 100. 

 s See p. 109. 



