HOST RELATIONS OF PARASITIC COWBIRDS 165 



ever, the frequency with which this sparrow is molested must vary 

 from time to time ; m an earher study, the same observer (Walkinshaw, 

 1936) noted that, out of 70 nests of the field sparrow, only four con- 

 tained eggs of the cowbird, whereas, in only 12 nests found in 1935, 

 four were parasitized. All but one of the parasitized nests were 

 deserted by the sparrows. 



In the nearby Edwin S. George Reserve, Sutton (1960, pp. 57-58) 

 found 59 nests of the field sparrow, of which 11 were parasitized. 

 However, he noted that he had never seen a fledgling cowbird attended 

 by field sparrows, and he concluded that, although parasitism appar- 

 ently cuts down sharply the percentage of nest-success for the host, 

 it does so without producing any parasitic young. In Maryland 

 and the District of Columbia, Stewart and Robbins (1958, pp. 329, 

 363) listed 11 cases of parasitism but they recorded data on some 265 

 field sparrow nests. 



As many as 5 cowbird eggs have been reported from a single nest 

 together wdth 2 of the field sparrow. 



The field sparrow quite often is tolerant of the cowbird eggs and 

 has been known on several occasions to rear the young parasites to 

 the fledgling stage. Walkinshaw's data, noted above, seems to have 

 involved an unusually intolerant group of bhds. 



Two records from South Dakota refer to the western race, arenacea, 

 of the sparrow and to the race artemisiae of the cowbhd. All the 

 other records involve the nominate race of each bird. 



Black-chinned Sparrow 



Spizella atrogularis (Cabanis) 



This little known bird has been recorded only twice as far as I 

 Iniow as a victim of the dwarf race of the bro'WTi -headed cowbird. 

 In the files of the U.S. Fish and Wildlife Service there is a record by 

 Stokely Ligon reporting a parasitized nest which was found 18 miles 

 above Santa Rosa, New Mexico, on July 6, 1913. The sparrow there 

 is the race evura. Bent (1958, p. 454) noted that Hanna collected two 

 parasitized nests in San Bernardino County, California. The local 

 race of the sparrow is cana. 



White-crowned Sparrow 



Zonotrichia leucophrys (Forster) 



The white-crowned sparrow is imposed upon infrequently b}^ the 

 brown-headed cowbird. There are only a few records, which are 

 outlined below. Rust (1917, pp. 37-39) found a nest with 4 eggs of 

 the sparrow and 1 of the cowbird in Fremont County, Idaho. Two 

 parasitized nests were found at Okotoks, southern Alberta, one by 

 Lings (Friedmann, 1949, p. 161) on June 11, 1930, the other by 



