HOST RELATIONS OF PARASITIC COWBIRDS 59 



against successful parasitism by the cowbird. Experimentally he 

 found that the lark will tolerate strange eggs or young in the nest 

 and that in the second half of the lark's breeding season, the food 

 supply is adequate and ample; thus it appears that other factors, as 

 yet undetermined, operate against the occurrence of cowbird parasit- 

 ism. In a period of many years in southern Quebec, Terrill (1961, 

 p. 4) found 201 nests of the horned lark and, of these, only 3 were 

 parasitized. 



Tree Swallow 



Iridoprocne bicolor (VieiUot) 



The tree swallow is a rarely imposed upon victim but one which, 

 Kumlien and Hollister (1903, p. 105) wrote, "often becomes the 

 foster parent of the cowbird" in Wisconsin. Still earlier, also in 

 Wisconsin, F. L. Grundtvig (1894, p. 122) wi"ote of having seen a 

 female brown-headed cowbu'd looking into the nest of a tree swallow 

 on May 28 and, on July 19, of seeing five yomig cowbirds among a 

 large flock of young tree swallows. More recently, Robbins (1947, 

 p. 135) reported a nest with 7 eggs of the swallow and 1 of the cowbird, 

 found on Jime 13, 1947, by Carl Richter in Oconto County, Wisconsin. 

 Years ago I suggested (1929, p. 234) that, if the brown-headed cowbird 

 parasitizes tree swallows in Wisconsin to any extent when it still is 

 not known to do so elsewhere, the case might be that the swallows 

 there used shallower and wider-mouthed nesting cavities (possibly 

 nest boxes) than in other areas; however, this is not known to be so. 

 It is strange that every one of the few records should come from a 

 single area, especially since the tree swallow is not parasitized in the 

 remamder of its ranges. The parasite in aU these cases is the eastern 

 form, M.a. ater. 



Bank Swallow 



Riparia riparia (Linnaeus) 



The bank swallow is an unusual and unlikely victim of the brown- 

 headed cowbird. There is one record. In the R. M. Barnes collec- 

 tion, presumably now in the Chicago Natm'al History Museum, is a 

 parasitized set of 6 eggs of the bank swallow and 1 of the cowbird 

 (race M.a. ater), collected in Illinois by W. E. Loucks. This record 

 involves the nominate race of the host. 



Barn Swallow 

 Hirundo rustica Linnaeus 



The barn swallow is a very infrequent victim. The known instances 

 are as follows: Anderson (1907, p. 299) listed it as a cowbird host in 

 Iowa, a listing which he based on the record of a parasitized nest found 

 by J. V. Crone and originally reported by Savage (1895, p. 36); a 

 parasitized set, consisting of 4 swallow eggs and 1 cowbird egg, col- 



