96 



BULLETIN 86, UNITED STATES NATIONAL MUSEUM. 



Maripa, on the Rio Caura, Venezuela, seem to average somewhat 

 more grayish (less ochraceous) on the light areas of the upper sur- 

 face, while the dark areas are not quite so brownish. Two specimens 

 from Encontrados (Zulia), Venezuela, are much more blackish above 

 than either the series from Guiana or Maripa; and one from the 

 Eio San Juan Oscuro, Colombia (No. 71705, Amer. Mus. Nat. Hist.), 

 is even darker, and also more ochraceous above and below. None of 

 thevSe color differences, however, appear to be more than individual. 

 Specimens from Cayenne and British Guiana are in color like those 

 from Brazil ; and one from Margarita Island, Venezuela, is just the 

 same. Nor am I able to distinguish from Venezuela birds a single 

 example from Guayaquil, Ecuador (No. 21992, Acad. Nat. Sci. 

 Phila). Specimens from different parts of the range of Chordeiles 

 acutipennis acutipennis average as follows: 



Localities. 



Middle 



toe. 



Nine males, from Venezuela 



Two males, from the Guianas 



Three females, from Venezuela 



Five females, from British Guiana and French Guiana 

 One female, from Brazil 



13.7 

 13.1 



13.9 

 12.9 

 14 



It will be noticed that the birds from the Guianas average smaller 

 than those from other localities, but this is possibly due to the small- 

 ness of the series. 



Individual variation in size is very great, as the table of detailed 

 measurements will show. Likewise there is a wide range of color 

 difference, unattributable to sex, age, or season. In some cases the 

 white subterminal tail-bar of the male is practically absent. There 

 are also two, or rather four, styles of plumage, or phases, as they 

 doubtless really are ; a gray, and an ochraceous or tawny phase, each 

 of these with a light and dark extreme. All these are connected by 

 various intermediates. These phases are not so strongly marked as 

 the red and gray plumages of Otiis asio, but are nevertheless readily 

 recognizable, although birds in the extremes of these phases seem to 

 be uncommon. Gray birds seem to be the more numerous. In the 

 gray phase the upper surface almost entirely lacks rufous and ochra- 

 ceous, most of the light areas being white or grayish ; and the lower 

 parts have the ochraceous confined to the jugulum, and the buff of the 

 remaining inferior area to the posterior portion. In the ochraceous 

 phase the blackish areas above are somewhat more brownish and the 

 light areas mostly tinged with ochraceous or buff; the lower parts 

 are strongly tinged with ochraceous or tawny throughout; and the 



