NEVADA BROWN-HEADED COWBIRD 451 



MOLOTHRUS ATER ARTEMISIAE Grinnell 



Nevada Brown-Headed Cowbird 

 HABITS 



This large race of the species breeds in western Canada and in the 

 northern part of western United States and winters south to southern 

 Texas and Mexico. It was originally described by Joseph Grinnell 

 (1909) as similar to the eastern cowbird, "but somewhat larger, with 

 proportionally longer and more slender bill; similar to M. a. obscurus 

 (Gmelin), of the lower Sonoran zone in Arizona and southeastern 

 California, but larger." In its plumage changes, feeding, and general 

 habits it does not differ materially from its better-known eastern 

 relative. It is reported to eat the Mormon cricket and many other 

 harmful insects, an action greatly to its credit. 



Spring. — Dr. Ian McT. Cowan (1939) writes of the arrival of these 

 cowbirds in the Peace River District of northeastern British Columbia: 

 "Ten cowbirds were seen on May 6 at Tupper Creek but not until 

 May 10 did they become numerous. On that date a flock of about 

 forty males and four females and another containing fifty-five males 

 and one female appeared and fed for some time in the pasture on 

 Austin's ranch. Later on May 14 the proportion of females increased 

 to about a quarter of the aggregate of birds in each flock and flocks 

 up to fifty birds were common. * * * At its maximum the sex ratio 

 was approximately one female to three males. In May the main hosts 

 of the cowbirds were hermit thrushes and juncos." 



Nesting. — Friedmann (1929) gives a list of 52 birds known to have 

 been imposed upon by the Nevada cowbird; they belong mainly to 

 the same classes of birds that are hosts of the eastern cowbird and 

 including some of the larger birds, such as the blackbird, towhee, 

 grosbeak, catbird, brown thrasher, and robin. Eggs have been 

 found in a nest of the California gull and of the ferruginous rough- 

 legged hawk, which were, of course, wasted eggs. 



Eggs. — The eggs of the Nevada cowbird are similar to those of the 

 eastern cowbird, and the measurements have not been separated from 

 those given by Bendire (1895) for the eastern form; they average 

 slightly larger. The measurements of 40 eggs average 21.8 by 16.8; 

 the eggs showing the four extremes measure 25.4 by 16.8, 23.4 by 

 18.0, 19.8 by 17.0, and 20.1 by 15.2 millimeters. 



Behavior. — Coues' (1874) account of the behavior of this cowbird 

 in the west is worth quoting, as follows: 



Every wagon-train passing over the prairie in summer is attended by flocks of 

 the birds; every camp and stock-corral, permanent or temporary, is besieged by 

 the busy birds, eager to glean sustenance from the wasted forage. Their famili- 



