HOST RELATIONS OF PARASITIC COWBIRDS 75 



should be noted that A. O. Gross {in Bent, 1949, p. 160) found the 

 bu-d to be a fairly frequent victim. He writes that, although he had 

 seen less than 15 nests of this thrush, four of them had been para- 

 sitized — two in Maine and two in Michigan. Furthermore, Cowan 

 (1939, p. 44) at Tupper Lake, Peace River, British Columbia, reported 

 that seven out of eight nests found were parasitized. These Tupper 

 Lake records probably are better allocated to the nominate form of the 

 host than to Jaxoni as I previously thought (1943, p. 354). In southern 

 Quebec, over more than a half century of observation, Terrill (1961, 

 p. 5) found 120 nests of the eastern hermit thrush, Jaxoni; of these, 

 only six, or five percent, contained eggs or young of the cowbird. 

 Other reports of parasitism on the eastern hermit thrush are on record 

 from Alberta (Godfrey, 1952, p. 170), Montreal (Wintle, 1896, p. 90), 

 Michigan (Swales, 1892, p. 45), and New York (Short, 1894, pp. 255- 

 256; Burtch, 1910, p. 139). There is a single record for the subspecies 

 auduhoni: a set taken in Valley, Utah, June 12, 1912, comprising 3 

 eggs of the host and 1 of the parasite, now in the R. M. Barnes collec- 

 tion of the Chicago Natural History Museum. There must have 

 been an earlier record, since Bendire listed H.g. auduhoni as a cowbird 

 host in his 1895 list. A parasitized set of eggs of the host race polionota 

 was taken in Mono County, California, June 6, 1933; it is now in the 

 collections of the Western Foundation of Vertebrate Zoology. 



Swainson's Thrush 



Hylocichla ustulata (Nuttall) 



Swainson's thrush has been reported very seldom as a cowbii'd host; 

 less than a dozen instances have come to my notice. The data 

 involve two races of the host and thi'ee of the parasite. Smith (1926, 

 p. 245) found a nest of the nominate race of the thrush near San Jose, 

 California, containing 2 eggs of the host and 1 of the brown-headed 

 cowbird (obscurus); another parasitized set, taken near Riverside, 

 California, June 26, 1950, is now in the San Bernardino Countj^ 

 Museum; these are the only instances for each of the foregoing sub- 

 species. Horsbrugh (1918, p. 495) noted three cases of parasitism of 

 the eastern race H.u. swainsoni at Sylvan Lake, Alberta; to this may 

 be added a fourth case from Edmonton, a set now in the Rowan 

 collection at the University of Edmonton. Stansell (1907, p. 120) 

 recorded another from Alberta. All the Alberta records involve the 

 northwestern race of the parasite, M.a. artemisiae, as do also two from 

 Minnesota (Cass and Kjttson Counties) Hsted by Roberts (1932, p. 

 129), one from Minnesota listed by Sparkes (1953), and one from Reeves 

 Lake, TurnbuU Refuge, Spokane Coimty, Washington (from the files 

 of the British Columbia Nest Records Scheme). The eastern form 

 of the cowbird, M.a. ater, is involved in two instances of parasitism 



