HOST RELATIONS OF PARASITIC COWBIRDS 123 



mon host. Several records from Georgia (Chamberlain and Denton, 

 1949; Parkes, 1950; Chamberlain, 1958; Webb and Wetherbee, I960) 

 reveal that in this southeastern area, which recently has been invaded 

 by the parasite, the hooded warbler seems to be a rather frequently 

 chosen host. 



Wilson's Warbler 

 Wilsonia pusilla (Wilson) 



Wilson's warbler has been reported very seldom as a cowbird victim, 

 but locally it is probably a fairly common host. Fourteen records 

 have been noted, all but two from southern California (race chryseola) : 

 one from eastern California and the other from Alberta {vsice pusilla) . 

 Most of the California records involve the small race of the cowbird, 

 M.a. obscurus; two from Mono County (Dixon, 1934, p. 36; Kowley, 

 1939, p. 251) and the record from Alberta refer to Al.a. artemisiae. 



In southern California, Willet (1912, p. 70) recorded three parasit- 

 ized nests in Ventura County; LaJeunesse (1923, pp. 31-32) found 

 five nests in Alameda County, each of which contamed eggs of the 

 cowbu'd. The last five nests were all found within one month in a 

 limited area, a fact which indicates that there the cowbird was making 

 much use of the nests of this warbler. M. C. Badger wrote me that 

 the bird is a very common victim in southern California. Ungiish 

 (1931, p. 214) found a parasitized nest in San Benito County; Peyton 

 (1931, p. 162) found another in Ventura County. Other records in 

 private egg collections, transmitted to me without definite localities, 

 are three in number. Talmadge (1948) recorded a cowbird egg from 

 the nest of either Wilsonia pusilla or Vermivora celata at Fern bridge, 

 Humboldt County, California. Although this record is uncertain, it 

 probably involves Wilsonia. 



The one Alberta record was found by T. E. Randall at Boyle, 

 Alberta, on May 27, 1934 — a nest with 4 eggs of the warbler and 

 1 of the cowbird. 



Canada Warbler 



Wilsonia canadensis (Linnaeus) 



The Canada warbler is a regular but infrequent host of the brown- 

 headed cowbird. It has been loiown to be imposed upon by the 

 nominate race of the parasite in Ontario, New Brunswick, New York, 

 Indiana, Michigan, and Minnesota. Recently, it has been found by 

 Street (Houston and Street, 1959, p. 176) to be molested by the 

 western race, artemisiae, at Nipawin, Saskatchewan. Instances of 

 this warbler as a victim of the eastern brown-headed cowbird may be 

 noted as follows. C. T. Black (1955, p. 23) listed three cases in 

 Lapeer and Macomb Counties, Michigan, and Nolan (1958, p. 417) 

 added another one from Dunes Park, Indiana. Besides these, there 



