HOST RELATIONS OF PARASITIC COWBIRDS 169 



sympatric with the latter throughout the entire breeding range of the 

 parasite, it is parasitized probably more often and over a greater area 

 than any other bird. The total number of records is very great. 

 After accumulating over 900, I stopped noting them except for records 

 of special interest. The data came from every province of Canada 

 and every state of the United States included in the breeding ranges 

 of both birds, illl three races of the parasite are involved, and no less 

 than 17 races of the song sparrow: melodia, atlantica, euphonia, juddi, 

 montana, inexpectata, merrilli, Jisherella, morphna, cleonensis, gouldii, 

 samuelis, pusillula, heermanni, cooperi, fallax, and saltonis. So far, 

 none of the purely Mexican races have been reported as fosterers of 

 the cowbird, but this fact is probably due more to a lack of human 

 observation than to any actual immunity of the bird to cowbird 

 parasitism. 



There is no need to detail actual instances for the various races of 

 the song sparrow since such cases already have been given in my earlier 

 summaries (1929, pp. 225-226; 1934, pp. 113-114; 1938, p. 50; 1943, 

 p. 356; 1949, pp. 161-162). However, a few additional records of 

 infrequently reported races of the host species should be mentioned. 

 Talmadge (1948, p. 273) found a nest of the subspecies cleonensis witli 

 3 eggs of the sparrow and 1 of the dwarf cowbird at Mad River Bar, 

 Humboldt Co., Cahfornia, in June, 1947. M.m. fallax was reported 

 as a cowbird host in Wyoming by McCreary (1957, p. 94). M.m. 

 morphna was seen feeding a fledgling cowbird at Comox, British 

 Columbia, by W. R. Goodge and Z. M. Schultz (1956, p. 404). M.m. 

 saltonis is represented by five parasitized sets of eggs, all from Yuma, 

 Arizona, and now in the collections of the University of Arizona 

 (J. T. Marshall, Jr., in Utt.). For M.m. samuelis, two instances of 

 cowbird parasitism (Johnston, 1956, p. 29; 1960, p. 138) are of interest 

 as evidence of the cowbird's laying in nests within salt marsh vegeta- 

 tion. Johnston noted that, in the San Francisco Bay marshes, the 

 song sparrows built their nests within lumps of pickleweed (Salicornia 

 ambigua), cordgrass {Spartina foliosa) , or gumplant (Grindelia cunei- 

 folia) . The two nests that had been parasitized were found in gumplant 

 shi'ubs, which, of the three plants, is the most similar to the nonswamp 

 vegetation of the cowbird's more usual habitat. For M.m. 

 inexpectata, two additional instances of cowbird parasitism in the 

 Vanderhoof region, British Columbia, were recorded by Munro (1949, 

 p. 113). 



In recent years, not only many hundreds of additional cases, 

 but also much more quantitative data on the host-parasite relations 

 have become available. Hicks (1934) found that 135 out of 398 nests 

 (34 percent) of this sparrow were parasitized in Ohio. Nice (1937a, 

 pp. 196-201; 1937b, p. 159), also in Ohio, reported that 98 out of 



