The Cowbird: A Parasite 



By HARRY E. ELDER, Monticello, Ind. 



THE common name for the species generally known as the Cowbird 

 varies with different people and with different sections of the country. 

 Cow Blackbird, Cow Bunting, Lazy Bird, Brownheaded Blackbird, and 

 other appellations are among the synonyms in use. Whether most appropriate 

 or not, usage seems to be crystallizing upon the term 'Cowbird,' for the reason 

 that members of the species are so often found among cows in pastures. The 

 reason for this association with cattle is not exactly known. Some writers see 

 no relation between such association and the life of the bird, while others 

 believe that insects, driven from the grass and weeds by the cattle, furnish the 

 foundation for such a habit. 



It is as a parasite upon other species of birds that the Cowbird is most 

 interesting. It never builds a nest of its own, it does not incubate its own eggs 

 and it takes no care whatever of its young. Its eggs are deposited in the nests 

 of other birds, usually smaller than itself, and the foster parents incubate them 

 and feed them along wdth their own. Most evidence indicates that the Cow- 

 bird deposits its eggs directly in the nests of its victims. Not less than ninety- 

 one species, according to Bendire, are victimized in this manner. Since its 

 egg is, as a rule, larger than those of the rightful owners of the nests, it receives 

 most of the body heat during the period of incubation and frequently hatches 

 a day or two ahead of the other birds. This gives the young Cowbird the 

 advantage over his nest-mates, with the result that he gets the greater amount 

 of the food brought to the nest and soon starves the others or shoves them 

 entirely from the nest. According to my own observations the number of 

 Cowbird eggs in a single nest may range from one to three, along with from 

 one to five of the rightful owner. Greater variations than this have been 

 reported. The Report of the New York State Museum for 191 2 states that in 

 every instance the Cow^birds destroy the rightful owners of the nests. Barrows, 

 in 'Michigan Bird Life", however, states that the Song Sparrow frequently 

 rears one or two of its own young in addition to one or more yoimg Cowbirds. 

 My own observations show that this is also true of the Field Sparrow, the 

 Towhee, and the Catbird. 



The observations upon which this paper is based were made in the vicinity 

 of Winona Lake, between June 14 and August 20, 1920. A report of these 

 observations as a whole and of specific instances will make clear the nature of 

 the Cowbird. 



On June 17 I was fortunate enough to find a Towhee's nest containing four 

 eggs, all very much alike. Three were white with reddish brown spots well 

 distributed over the entire surface and one was slightly brownish with the 

 spots not so pronounced as in the other three. They were all so nearly the 

 same size, about .8 by .65 inches, that from the eggs alone no one could have 



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