HOST RELATIONS OF PARASITIC COWBIRDS 101 



black-throated blue warbler feeding a young cowbird much larger than 

 she was. Kells (1887, and 1902) recorded two parasitized nests 

 in Ontario; another Ontario record is a parasitized nest found by 

 Saunders at Durham, Gray Count}^, on June 22, 1909, and reported 

 by BaiJhe and Harrington (1937, p. 245). In New York, W. L. Ralph 

 collected three such nests, which are now in the U.S. National Museum. 

 Terrill (1961, p. 7) discovered three instances of cowbu'd parasitism 

 in seven nests which were found in southern Quebec in the course of 

 nearly 60 years of observation in that region. All the records involve 

 the nominate race, both of host and parasite. 



Myrtle Warbler 



Dendroica coronata (Linnaeus) 



The myrtle warbler is a commonly utilized host in southern Canada, 

 but seldom has it been recorded elsewhere in this capacity. It 

 has been noted as a victim of the cowbird in Alberta, Saskatchewan, 

 Ontario, Quebec, Maine, Michigan and Wisconsin. Dr. Paul Harring- 

 ton wrote to me that near Wasaga Beach, South Georgian Bay, 

 Ontario, he examined 38 nests, no less than 25 of which contained eggs 

 of the cowbird; 20 nests had 1 parasitic egg; three had 2 each; and 

 two had 3 each. One nest had a cowbird's egg imbedded in its side, 

 where the warbler had built a new nest lining over the egg. Bent 

 (1953, p. 250) quotes Harrington that "it would not be exaggerating 

 to say that two-thu*ds of the initial nests are parasitized. The egg or 

 eggs of the cowbird are often deposited before the nest is completed, 

 leading to many a deserted nest. Twice I have found a cowbird's 

 egg imbedded, as so often happens in the yellow warbler's nest, but 

 in both cases yet another was in the nest with the owner's. Twelve 

 percent of the nests with eggs of the cowbird were deserted, but none 

 in which the owner's eggs were also present. Generally but one of 

 the parasite's eggs was found, occasionally two and rarely three." 



Bent cites F. A. E. Starr as saying that, of 30 nests examined, he 

 had yet to find one which did not contain from 1 to 3 eggs of the 

 cowbird. In southern Quebec, out of a total of 33 nests examined, 

 Terrill (1961, p. 7) noted two instances of cowbird parasitism on this 

 warbler. 



In Maine, Knight (1908, pp. 341-342) hsted the myrtle warbler as 

 a local cowbird host, and C. H. Morrell collected a parasitized set of 

 eggs at Pittsfield, on May 26, 1891. This set, now in the U.S. National 

 Museum, may have been the basis for Knight's statement. In Michi- 

 gan, Van Tyne (1924, p. 169) found a parasitized nest near Hessel, 

 Macldnaw County, on June 20, 1919, and Root (1942) observed a 

 pair of myrtle warblers feeding a fledgling cowbird. The foregoing 

 records all involve the eastern race of the cowbird. 



