86 U.S. NATIONAL MUSEUM BULLETIN 233 



cowbird are numerous, it is relatively unmolested by the parasite. 

 Occasionally this host may bury the cowbird's egg under a new nest 

 lining if it has no eggs of its own at the time; such a case was reported 

 by Jacobs (1903, p. 19). The j^ellow-throated vireo has been known 

 to rear cowbirds successfully to the fledging stage. All the records 

 of parasitism on this bird involve the typical race of the cowbird. 



Solitary Vireo 

 Vireo soliiarius (Wilson) 



The solitary vireo is parasitized less commonly than the white-eyed 

 and the yellow-throated and much less so than either Bell's or the 

 red-eyed vireos. I know of 20 records, involving four races of this 

 bird: solitarius (in Massachusetts, New York, Michigan, and Minne- 

 sota), alticola (in West Virginia), plumbeus (in Alberta, Montana, New 

 Mexico, and Arizona), and cassinii (in Oregon and California). All 

 three races of the parasite are involved : ater is the form parasitic on 

 solitarius, plumbeus, and alticola; artemisiae and obscurus both vic- 

 timize plumbeus and cassinii. Although a majority of the reported 

 instances are egg records, the fact is known that the solitary vireo 

 successfully may rear young cowbirds, A. H. Miller (1948, p. 92) 

 saw solitary vkeos with young cowbirds in the open pine woods of 

 Powder Kiver County, Montana, in June, 1947; similar observations 

 also have been reported from Minnesota by Roberts (1932, p. 176). 

 However, judging by not very abundant data, it seems that the soli- 

 tary vireo is somewhat more prone to cover over cowbird eggs with 

 new nest lining than to allow the young to hatch ; this habit the vireo 

 reveals more than the other species of its family. Allen (1913, pp. 

 296-300) and Greene (1892, pp. 8-9) have published accounts of such 

 behavior. 



Since the records for the races alticola, plumbeus, and cassinii are 

 still few in number, they can be itemized here, V.s. alticola so far 

 is known from two instances, Dickey (1941, pp. Ill, 112) found a 

 nest with 3 eggs of the vireo and 1 of the cowbird near Cheat River, 

 West Virginia, and another nest with a cowbird egg embedded in its 

 wall at Point Mountain, Randolph County, West Virginia. The 

 western subspecies, V.s. plumbeus, is known as a victim in the follow- 

 ing localities: Power River County, Montana (Miller, 1948, p. 92); 

 Grassland, Alberta, where a parasitized set of eggs was collected June 

 8, 1935, a set now in the William Rowan collection at the University 

 of Alberta; Boyle, Alberta, where a set of eggs was collected May 28, 

 1934, by T. E. Randall; New Mexico, according to Bailey (1928, p. 

 661) on information received from Stokley Ligon; and Arizona, where 

 Alex Walker found a nest with 3 eggs of the vireo and 1 of the dwarf 

 race of the cowbird on June 15, 1932, in Montezuma Canyon in the 



