HOST RELATIONS OF PARASITIC COWBIRDS 87 



Huachuca Mountains at 5400 feet elevation. Finally, the subspecies 

 V.s. cassinii was found to be parasitized at Yosemite, California, by- 

 Michael (1935, p. 178) and near MUton, San Joaquin County, Cali- 

 fornia, by W. B. Sampson. The latter informed me that on May 30, 

 1932, he found a nest containing 2 eggs of the cowbird together with 

 2 of the vireo. Kebbe (1954, p. 51) found another parasitized nest 

 on May 6, 1954, at McKay Creek near North Plains, Washington 

 County, Oregon. Bent (1958, p. 453) noted that J. Stuart Rowley 

 had found a parasitized nest at Lake Arrowhead, San Bernardino 

 County, California. Two similar sets, collected in the same county, 

 are now in the San Bernardino County Museum. In the collection 

 of the California Academy of Sciences there is a cowbird egg taken 

 from a Cassin vireo nest in Alameda County, May 13, 1934, by H. 

 W. Carriger. 



Yellow -green Vireo 



Vireo flavoviridis (Cassin) 



This vireo is a very poorly known victim; only a single observation 

 has been reported. Lawrence (1874, p. 280), quoting Grayson, wrote 

 that, near Mazatlan, Stnaloa, Mexico, the yellow-green vireo is "the 

 preferred host" of the dwarf race of the brown-headed cowbird. 

 Lawrence's statement is the basis, in turn, for that of Salvm and 

 Godman (1886, p. 451). 



Red-eyed Vireo 



Vireo olivaceus (Linnaeus) 



The red-eyed vireo is one of the commonest hosts used by the 

 brown -headed cowbird. No species is molested more — either in the 

 total number of cases or in the percentage of nests that are para- 

 sitized. The cases are so numerous that it is possible only to estimate 

 them; a total in excess of 875 was noted finally, at which point there 

 seemed no reason to accumulate any more. The records range from 

 Alberta, British Columbia, New Brunswick, Ontario, Quebec, and 

 Saskatchewan, in Canada, to the following states in the United States : 

 Alabama, Arkansas, Colorado, Connecticut, Delaware, District of 

 Columbia, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, 

 Maryland, Massachusetts, Michigan, Minnesota, Montana, New 

 Jersey, New York, North Dakota, Ohio, Oklahoma, Pennsylvania, 

 Rhode Island, South Dakota, Tennessee, Texas, Virginia, Washington, 

 West Virginia, Wisconsin, and Wyoming. All three races of the 

 parasite are involved: obscurus in the San Antonio area of Texas, 

 artemisiae in the region from British Colombia east to Saskatchewan 

 and south to Colorado and Wyoming, and ater in the remaining 

 localities. 



630590—63 7 



