BLACKBIRDS, ORIOLES, ETC. 285 



cowbird, or cow blackbird, deposits her eggs in the nests 

 of other birds, usually some smaller variety, as she builds 

 no nest, but leaves her eggs solely to the care of the foster 

 parents. Nests of the yellow warbler, bobolink, indigo 

 bunting, song sparrow, field sparrow, towhee, yellow- 

 breasted chat, red-winged blackbird, and redstart are fre- 

 quently used for this purpose. Sometimes the eggs of the 

 cowbird closely resemble those of the owner of the nest, as 

 is true with the eggs of the towhee, chat, and cardinal. 



Such birds as the catbird, wood thrush, and prairie 

 horned lark resent such imposture, and destroy or remove 

 the cowbird's eggs. Some of the smaller species, as the 

 yellow warbler, unable to cope with the situation, build 

 over the intruder's eggs, since the cowbird often deposits 

 her eggs before the owner of the nest begins to lay. I have 

 known j^ellow warblers to repeat this operation three times 

 in one nest in their effort to rid themselves of the unwel- 

 come eggs. If hatched, the intruders monopolize the nest, 

 crowding the nestlings from their own cradle or starving 

 and smothering them. 



YELLOW-HEADED BLACKBIRD 



Like the dickcissel, the occurrence of the Yellow-headed 

 Blackbird is uncertain and erratic. In many sections from 

 the Mississippi to the Pacific they may be found breeding 

 singly or in small flocks, usually returning annually to the 

 same swamps and marshes. East of the Mississippi their 

 appearance is uncertain and rare. During years of study 

 and observation in northern Illinois, I never discovered this 



