THE GENUS CHORDEILES SWAINSON — OBERHOLSER. 91 



deiles acutipennis infenor ^ are comparatively local ; while Chordeiles 

 acutipennis micromeris^ is somewhat restricted in distribution. 



The ranges of the two South American forms, Chordeiles acuti- 

 2)ennis acutipennis and Chordeiles acutipennis exilis, seem to be 

 practically continuous; but, so far as known, there is a wide gap 

 between the northern breeding limit of Chordeiles acutipennis acuti- 

 pennis in northwestern Colombia and the nearest point in the sum- 

 mer distribution of Chordeiles acutipermis micromeris^ in Guate- 

 mala or British Honduras. By all the collecting that has been done 

 in the intervening countries of Central America — Salvador, Hon- 

 duras, Nicaragua, Costa Rica, and Panama, the last two particularly — 

 not an actual breeding record has been obtained. If the species 

 really does breed in any part of this area it must be very rare. The 

 range of Chordeiles acutipennis texensis is continuous with that of 

 both Chordeiles acutipennis micronneris ^ and Chordeiles acutipennis 

 inferior.^ 



Zonal distribution. — In South America this species occupies the 

 Lower Tropical Zone of the Neotropical Region; in Mexico the 

 Lower Tropical, Upper Tropical, and Lower Austral zones, and in 

 places part of the Upper Austral Zone ; in the United States chiefly 

 the Lower Austral Zone, but also parts of the Upper Austral Zone. 

 Although the details of its zonal affinities are not very well known, 

 particularly in South America, most of the subspecies seem to have 

 fairly definite zonal distribution. Two races, Chordeiles acutipennis 

 acutipennis and Chordeiles acutipennis exilis, are apparently each 

 confined to a single life zone; one, Chordeiles acutipennis texeTisis, 

 to two zones; and each of the two other forms to three zones. In 

 some cases a zone is not fully, even but little occupied^ this being 

 noted principally with regard to the Upper Austral Zone. 



Phylogeny. — The South American origin of Chordeiles acutipermis 

 may be taken almost for granted. Furthermore, that Chordeiles 

 acutipennis acutipennis should be considered the primitive and parent 

 form is indicated by its present South American distribution, its ex- 

 tensive range, its uniformity over this wide area, its lack of migration, 

 and the relation of its characters of color and size to those of other 

 subspecies. In western Peru it has been modified, in that more arid 

 climate and consequently changed environment, into Chordeiles acuti- 

 pennis exilis, a form of approximately the same size but more pallid 

 coloration. The northwestward dispersal of the species has been 

 through Central America and Mexico to the southwestern United 



1 See p. 109. 

 * See p. 100. 



