54 BULLETIN 86, UNITED STATES NATIONAL MUSEUM. 



Chordeiles mrginianus hesferis. Such are No. 13473, L. B. Bishop, 

 adult male, Stump Lake, North Dakota, August 4, 1905; and No. 

 26715, Academy of Natural Sciences of Philadelphia, adult female, 

 Huron, South Dakota, July, 1881. Birds of this description may, 

 ' however, almost always be separated from Chordeiles mrginianus 

 hesperis by their pale, lightly barred under surface. The other ex- 

 treme is a bird which has the markings of the upper parts very 

 whitish, numerous, and extensive (No. 26717, Acad. Nat. Sci. Phila., 

 adult male, Huron, South Dakota, July, 1881). Another variation 

 produces a bird in which most of the light markings on back, scap- 

 ulars, pileum, and hind neck are buff, cream buff, or cream color (No. 

 19835, Carnegie Mus., adult male, Madison, Minnesota, June 4, 1891). 

 In some examples the lower tail-coverts and the middle of abdomen 

 are almost immaculate white. There is some variation also in the 

 depth of the color and in the width of the dark brown bars on the 

 posterior lower parts. As may be seen from the table of measure- 

 ments, this form varies greatly in size, apparently more so than some 

 of the other races. A single adult female (No. 1960, collection of 

 L. B. Bishop), from Towner County, North Dakota, taken June 11, 

 1895, is very brownish, and ochraceous or buffy both above and below, 

 and is practically indistinguishable in appearance from very typical 

 female Chordeiles vh^ginianus howelli^ thus strikingly different from 

 any of the females of Chordeiles virginianus sennetti examined. It 

 is, of course, just possible that this individual wandered northward 

 from the range of Chordeiles virginianus howelli^ but it seems better 

 to regard it as an abnormal variation of Chordeiles mrginianus sen- 

 netti. 



This subspecies has a more restricted distribution than most of 

 the others. The birds from Huron, South Dakota, and from eastern 

 South Dakota and eastern North Dakota in general are most typical, 

 in that they carry to the extreme the characters of the subspecies; and 

 the type of this race, from 50 miles west of the Pembina Mountains, is 

 practically the same as these. Specimens representing the breeding 

 bird of Dickinson County, Iowa, and Madison, western Minnesota, 

 verge toward Chordeiles mrginianus virginianus^ but are much nearer 

 the present race. Examples from Strater, and from Darnall's Ranch, 

 Dawson County, in northeastern Montana, are darker above, and 

 very close to Chordeiles virginianus hesperis^ but are, as a whole, 

 nearer Chordeiles v. sennetti. A single specimen (No. 171803, 

 U.S.N.M., June 3, 1889) from Fort Keogh, central eastern Mon- 

 tana, seems to incline a little toward Chordeiles virginianus howelli ^ 

 in its more brownish and ochraceous colors above. Females from 

 Towner County, North Dakota, are apparently darker on the upper 

 surface than the females from farther south, but the males from the 



1 See p. 57, 



