THE GENUS CHOKDEILES SWAINSON OBEKHOLSER. 89 



once evident on comparison of specimens. In adults these color 

 variations consist in the darkness or lightness of the upper surface, 

 due to the brownness or blackness of the dark areas, and particu- 

 larly to the fineness and amount of the light mottling, together with 

 the wliitish, grayish, ochraceous, or tawny hue of these markings; 

 depth or paleness of lower surface, and of its buffy, ochraceous, or 

 tawny tinge; the width of the black bars on the posterior lower 

 surface, and of the light bars on the tail ; and the size of the light 

 wing-spot. 



In fact, so conspicuous and often coordinated are many of these 

 dilfferences, particularly those affecting the general coloration of 

 upper and lower parts, that they form several more or less well- 

 defined color phases, which are, however, more striking in some of 

 the subspecies than in others. These phases really number four, 

 though two of them are light and dark extremes of the gray 

 and ochraceous, or tawny, phases. They are all more fully treated 

 under Chordeiles acutipennis acutipennis,^ in which race thej^ are 

 very well defined. It is interesting to note that, while in C?i07'- 

 deiles virginianiis these buffy, ochraceous, or tawny variations are 

 largely geographical, they are in the present species almost wholly 

 individual. The gray and ochraceous phases of this species are 

 almost if not quite as well marked in juvenal birds of all ages as in 

 the adults, a proof, if any were needed, that these color phases are 

 not due to age. 



Geographical variation. — To the three subspecies of Chordeiles 

 acutipennis currently recognized, two are now added, making thus 

 five. All the races are wholly or mainly continental, and corre- 

 spond fairly well to the characteristics exhibited by representatives 

 of other species occupying the same areas. The typical wide-ranging 

 South American Chordeiles acutipennis acutipennis is a small, dark 

 race ; the Peruvian Chordeiles acutipennis exilis, small and light ; the 

 Yucatan Chordeiles acutipennis micromeHs^^ of moderate size and 

 rather pale coloration; the Lower California Chordeiles acutipennis 

 inferior^ rather large and of light color ; and ChordeUes acutipennis 

 texeTisis, large and pale. It is noticeable also that the two southern- 

 most forms — Chordeiles acutipennis acutipennis and Chordeiles acu- 

 tipennis exilis — are the smallest, and that the size increases regularly 

 northward through Chordeiles acutipennis micromeris ^ and Chor- 

 deiles acutipennis inferior,^ reaching its maximum in the northern- 

 most race, Chordeiles acutipennis texensis. In color the pale Peruvian 



1 See pp. 96-97. 

 = See p. 100, 

 8 See p. 109. 



13732°— Bull. 86—14 7 



