444 U. S. NATIONAL MUSEUM BULLETIN 2 1 1 



5 of vireos, 5 of flycatchers, and 5 of various other birds. Cowbirds 

 had deposited 115 eggs in these nests, only a single egg in 80 of them. 

 He estimated from his records that, approximately, for every cowbird 

 raised to a self-sustaining age there is a loss of three and one-third 

 birds of some smaller species. 



Before we condemn the cowbird for its parasitic habits, however, 

 it must be shown that the young birds sacrificed for the cowbirds have 

 more economic value than the parasites. Beal (1900) comments on 

 this point: "When a single young cowbird replaces a brood of four 

 other birds, each of which has food habits as good as its own, there is, 

 of course, a distinct loss; but, as already shown, the cowbird must 

 be rated high in the economic scale on account of its food habits, 

 and it must be remembered that in most cases the birds destroyed are 

 much smaller than the intruder, and so of less effect in their feeding, 

 and that two or three cowbird eggs are often deposited in one nest." 



Behavior. — Cowbirds are highly gregarious at all seasons: although 

 the females and mated males scatter out in their breeding territories, 

 in the vicinity there are generally to be found flocks of unmated or 

 promiscuous birds with which the breeding birds associate more or 

 less. They are sociably inclined toward each other and there seems to 

 be no jealousy among them. Friedmann (1929) never saw them 

 fighting, but Mrs. Nice (1937) has seen it five times, "the occasion 

 being disagreements between males during communal courting 

 parties." 



The outstanding features of the cowbird's behavior is its well-known 

 fondness for, or association with, grazing cattle from which it derives 

 its appropriate common name. In its association with these animals 

 it is quite fearless, searching for food about the heads of the grazing 

 animals or even between their feet, sometimes even alighting upon 

 their backs, where they are supposed to relieve the animals of annoying 

 insects. The movements of the cattle undoubtedly stir up grass- 

 hoppers and other insects, making them more easily available for the 

 birds. The statements by some earlier writers that cowbirds search 

 the droppings of cattle to feed on intestinal worms is not substantiated 

 by stomach analysis. 



On the ground the cowbird walks or runs, but seldom hops; while 

 feeding it often holds its tail erected high in the air, with the wings 

 drooping below it. Its flight in the air seems rather unsteady, much 

 like that of the red-winged blackbird, from which it can be distin- 

 guished in the mixed flocks by its smaller size. Cowbirds seem to 

 be on good terms with other blackbirds and starlings, associating 

 with them in enormous mixed flocks on their feeding grounds or 

 roosting with them at night. They also, sometimes, join with swallows 

 or martins in their night roosts. Forbush (1927), however, says 



