36 U.S. NATIONAL MUSEUM BULLETIN 233 



ment. However, the presence of the host's own eggs in the nest 

 tends to make the contest more unfavorable to the cychcal sequence; 

 in such a situation the cowbird's eggs are frequently accepted along 

 with the host's eggs which are already present. 



As might be expected of a purely instinctive behavioral reaction, 

 the victimized bird may at times cover over the wrong eggs. Mousley 

 (1916, p. 178) reported a yellow warbler's nest containing 4 eggs of its 

 own. and 1 cowbird egg, while 1 of the warbler eggs was covered over 

 by nest-lining. He removed the cowbu'd egg and raised the embedded 

 warbler egg, freeing it of the materials placed over it. Revisiting the 

 nest three days later, he found that the warbler had embedded 2 of 

 her own eggs. The interference caused by his well-intended actions 

 had the same effect as if a cowbird had deposited another egg in the 

 nest. 



In some species of hosts, the "flooring over" behavior has been 

 noted frequently, chiefly in the yellow warbler, which has been known 

 to follow this pattern repeatedly in cases where the parasite persisted 

 in revisiting the nest. This would often result in two-, three-, foiu-, 

 five-, and even six-storied nests, in the lower stories of which were 

 buried cowbkd eggs with or without some of the warbler's own. In 

 other species, this reaction behavior has been recorded less often, 

 sometimes only once or twice. However, the fact that it has been 

 found to occur indicates the wide distribution of the pattern. This, 

 in turn, seems to bear out Herrick's concept that what is involved is 

 an interruption of a basic cyclical pattern and not something peculiar 

 to one or a few host species. In still other frequently imposed-upon 

 hosts, such as the eastern phoebe, wood thrush, veery, ovenbird, 

 Maryland yellowthi"oat, rufous-sided towhee, and chipping sparrow, 

 flooring over has not been reported as yet. 



The following species have been fomid to bury cowbird eggs beneath 

 new nest linings: 



eastern kingbird chestnut-sided warbler 



eastern phoebe prairie warbler 



Acadian flycatcher Kentucky warbler 



Traill's flycatcher yellowthroat 



bush-tit American redstart 



catbird eastern meadowlark 



blue-gray gnatcatcher redwinged blackbird 



Bell's vireo Baltimore oriole 



yellow-throated vireo cardinal 



solitary vireo indigo bunting 



red-eyed vireo American goldfinch 



warbling vireo clay-colored sparrow 



prothonotary warbler white-crowned sparrow 



yellow warbler song sparrow 

 myrtle warbler 



