HOST RELATIONS OF PARASITIC COWBIRDS 71 



Brown Thrasher 



Toxostoma rufum (Linnaeus) 



Both subspecies of the brown thrasher, rufum and longicauda, are 

 parasitized occasionally by the brown-headed cowbird (subspecies 

 ater and artemisiae). This species is the largest passerine bird molested 

 by the parasite — except for accidental victims — and it is the largest 

 bird definitely known to have hatched and reared a young cowbird. 



Thirty-one actual records of cowbird parasitism have come to my 

 notice, reports that range from Quebec and Ontario to Saskatchewan 

 in Canada, and from Connecticut, Pennsylvania, Maryland, Illinois, 

 Michigan, and Iowa to Minnesota, Wisconsin, Kansas, North Dakota, 

 Nebraska, Missouri, Tennessee, and Oklahoma in the United States. 

 For many years J. A. Allen's observation of a female brown thi-asher 

 feeding a nearly full-grown fledgling cowbird in western Iowa in 

 1868, a report which was discussed by Baird, Brewer, and Ridgway 

 (1874, p. 155), remained unique. In recent years, however, similar 

 cases have been reported. Bent (1948, p. 371) noted an observation 

 by T. Moore concerning a thrasher feeding three young fledged cow- 

 birds, the details of w^hich were published later by the observer 

 himself (Moore, 1956, p. 558). More recently, Nickell (1955, pp. 

 90-91) has noted three nests of the brown thrasher containing chicks 

 of the cowbird, indicating that the greater size of the host does not 

 preclude the eventual success of the parasite. In two of the nests, 

 young thrashers were developing together with the cowbird chicks; 

 in the third, the cowbird chick also had nest-mates but it did not 

 survive to the point of leaving the nest. 



Long-billed Thrasher 



Toxostoma longirostre (Lafresnaye) 



All that is laiown of this species as a cowbird host is a report from 

 the late R. D. Camp, who informed me that he had found the thrasher 

 (subspecies sennetti) to be imposed upon by the dwarf race of the 

 parasite near Brownsville, Texas. 



Bendire's Thrasher 



Toxostoma bendirei (Coues) 



In the collections of the U.S. National Museum there is a set of 

 3 eggs of Bendire's thrasher with 1 of the dwarf brown-headed 

 cowbird collected by E. A. Mearns near Red Rock, Arizona, April 3, 

 1885. This is the only instance of cowbird parasitism known to me. 



Although a great number of the nests of this bird have since been 

 examined, the above record has remained unique, a fact which sug- 

 gests that Bendire's thrasher ordinarily is unmolested by the cowbird. 

 Brown (1901) wrote that over a nimiber of years he had examined 



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