The Cowbird: A Parasite 189 



unknown in all three cases. The tenth nest, found July 19, contained three 

 Sparrow eggs and one Cowbird egg. All four eggs had hatched by July 30, 

 but the nest was robbed and the birds destroyed, probably by a Hawk, on 

 August 3 or 4. 



The first Song Sparrow's nest, found June 28, is interesting because of the 

 large number of eggs and its subsequent history. When found there were five 

 Sparrow eggs and three Cowbird eggs. By 4 o'clock p.m. of, the same day, one 

 Sparrow egg had disappeared. By July 7, another was gone. On July 10, when 

 I visited the nest, I found two young Sparrows, two young Cowbirds, and one 

 egg of each; on July 12, three Sparrows, two Cowbirds, and one Cowbird 

 egg; on July 13, one Sparrow, and two Cowbirds. On the morning of the 

 15th the Sparrow was found dead; one Cowbird was found in a similar condi- 

 tion on the 1 6th. The remaining Cowbird, now receiving the food of the entire 

 brood, grew very rapidly and left the nest on July 17 or 18. The other three 

 nests were found late in July, after the nesting season was over, but each con- 

 tained one Cowbird egg. Repeated observations, between June 22 and August 

 18, of Song Sparrows feeding young Cowbirds tend to confirm Barrows' state- 

 ment that "probably this species rears more Cowbirds than any other species 

 which we have." 



On July 19, a nest of the Acadian Flycatcher, containing one Cowbird 

 about to leave the nest, was found. On this same date a member of this same 

 species was observed feeding a young Cowbird which had left the nest. The 

 small, frail, shallow nest of this Flycatcher makes it almost certain that it does 

 not raise any of its own young in the same brood with a Cowbird. 



In addition to the birds which I have found nesting which were victimized 

 by Cowbirds I have noticed several species feeding young Cowbirds which had 

 left the nest. The young Cowbirds, usually already much larger than their 

 foster parents, were always calling for food more frequently than it could be 

 found and carried to them. Indeed, after they were well able to fly, they fol- 

 lowed their foster parents about and almost incessantly repeated their hunger- 

 call. They were, undoubtedly, fed long after they were able to care for them- 

 selves. I have seen Vireos, Maryland Yellow-throats, and American Redstarts 

 imposed upon in this manner. If these birds had any offspring of their own, 

 I did not see them. They gave the young Cowbirds their undivided attention, 

 while the adult Cowbirds flitted merrily about, probably spying out new victims. 



During the period of my observations I saw at least ninety different species 

 of birds. Thirty-three of these were either nesting or feeding young which 

 had left the nest. Thirteen of these thirty- three were victims of the Cowbird. 

 In other words, almost 40 per cent of the species found nesting or feeding 

 young birds were rearing young Cowbirds. Probably, if the entire truth 

 were known, the figures would show a still higher percentage. Consider- 

 ing some single species, such as the Field Sparrow, Song Sparrow, Towhee, 

 Yellow Warbler, and Maryland Yellow-throat, there is every reason to 



