HOST RELATIONS OF PARASITIC COWBIRDS 111 



disappearance of Kirtland's warbler, after which the cowbird probably 

 would turn to other hosts in the area. 



Prairie Warbler 



Dendroica discolor (Vieillot) 



The prairie warbler is a bird whose relations with the brown-headed 

 cowbird cannot be appreciated from the published data. When I 

 first studied this warbler (1929, p. 246), I was led to consider it a very 

 uncommon victim of the eastern race of the brown-headed cowbird; 

 however, correspondence and discussions with experienced and reliable 

 egg collectors since then indicate that in some localities the prau'ie 

 warbler is a very frequently imposed upon host. Approximately 35 

 records have come to my notice, distributed from New York, Connecti- 

 cut, New Jersey, Maryland, the District of Columbia, Virginia, North 

 Carolina and Georgia to Tennessee, Arkansas, Missouri, Indiana, 

 Michigan, and Ontario. 



The most important study of this warbler and its relations with the 

 cowbird is that made in Michigan by Walkinshaw (1959). He found 

 18 nests of the warbler, five of which contained cowbird eggs. In 

 these 18 nests, 63 warbler eggs had been laid, from which hatched 31 

 young (49.2 percent), 20 of which (31.74 percent) lived to leave the 

 nest. The five parasitized nests contained 6 cowbird eggs, of which 

 only 1 produced a young cowbird that survived to the fledgling 

 stage. It would appear from these data that the prairie warbler is 

 not a host with which the cowbird is very successful, and also it would 

 appear that the cowbu'd is not a great check on the increase of the 

 warbler. Nolan (1958, p. 272) in Indiana suggests, however, that the 

 presence of the young cowbu'd in a nest is serious, if not fatal, to the 

 young warblers. He found the prairie warblers to be a frequent host 

 and stated that the cowbird eggs "invariably hatched before those of 

 the host. I have seen male warblers feeding cowbird nestlings before 

 their own eggs had hatched, and this doubtless contributed to the 

 usual quick starvation of the young warblers." 



At Cape May, New Jersey, Stone (1940, p. 877) noted two para- 

 sitized nests found by Turner McMuUen. He considered the prairie 

 warbler one of the favorite hosts of the cowbird in that locality. 



According to Bailey (1925, p. 129), this warbler has been known to 

 build a new nest floor or lining over a cowbird's egg and any of its own 

 that may be present and then start a new clutch. 



All the records refer to the nominate race of warbler and cowbird. 



Palm Warbler 



Dendroica palmarum (Gmelin) 



The palm warbler rarely is victimized by the brown -headed cowbuxl. 

 Only seven instances have come to my attention. They involve two 



