HOST RELATIONS OF PARASITIC COWBIRDS 141 



or nearly 40 percent, were parasitized; also in Ohio, Phillips (1951) 

 found 14 nests, of which 6, or 42.8 percent, were parasitized. The 

 latter observer reported that, in the total 14 nests, 41 bunting eggs 

 and 7 cowbu'd eggs were laid; these produced 18 fledged buntings 

 (43.9 percent) and one fledged cowbird (14.3 percent). 



In his study of this bunting, Twomey (1945, pp. 193-195) found 

 that 12 out of 33 nests, observed during two successive years, were 

 parasitized. In most of these cases, fatahties to some of the host 

 young occurred: about 30 percent of those that hatched failed to 

 reach the fledging stage. Twomey studied the growth of the nestlings 

 of both host and parasite and found that the presence of a young 

 cowbird decreased the growth rate of the 3'Oung buntings which were 

 its nest-mates and that the presence of two young cowbirds in a nest 

 proved fatal to the young of the fosterer. Using Twomey's data, 

 Lack (1947, p. 323) attempted to equate one yoimg cowbird with two 

 young buntings in the factor of feeding by the host adults. 



In the Edwm S. George Keserve of southeastern Michigan, Sutton 

 (1959, pp. 95-99) found 26 nests of the indigo bunting, of which 4 

 were parasitized. In these 26 nests, 53 bunting and 6 cowbird eggs 

 had been laid. Of these, 44 bunting and 3 cowbird eggs hatched; 

 of the 44 bunting chicks, 23 fledged successfuUy. None of the para- 

 sitized nests produced fledglings of either parasite or host. 



In southern Quebec, Terrill (1961, p. 9) found 30 nests, of which 

 6, or 20 percent, were parasitized. In most places where it is para- 

 sitized, the indigo bunting appears to be a frequently chosen fosterer. 

 Orduiarily, it does not attempt to rid itseK of the strange eggs so 

 frequently foisted upon it, but one instance has come to my notice 

 of an indigo bunting burying under a new nest lining a cowbird egg 

 which had been deposited before the host had laid any of its own. 



On other occasions, as indicated above, the indigo bunting has 

 been known to rear young cowbirds to the fledging stage. I saw 

 two such cases at Ithaca, New York, in 1921 and 1922, and one of the 

 earliest and one of the most complete accounts of this finch as a 

 cowbird fosterer — published by Ord in 1836 (pp. 68-69) — gives a detailed 

 record of the development of two young cowbu-ds in an indigo bun- 

 ting's nest. As many as 5 eggs of the cowbird have been reported in 

 a single next of this host (Pius, 1949) and as many as two young cow- 

 birds have been known to be reared in one nest (Ord, loc. cit. ; Bradley, 

 1948). 



Lazuli Bunting 



Passerina amoena (Say) 



The lazuU bunting is known as a victim of the brown-headed 

 cowbird in California, Colorado, Idaho, Montana, and Washington. 

 Two races of the parasite are involved — obscurus in southern Califor- 



