HOST RELATIONS OF PARASITIC COWBIRDS 129 



by Bent (1958, p. 144), establishes further corroboration. Out of 

 hundreds of redwing nests found by Trautman, only four were para- 

 sitized and these were isolated nests, considerably removed from the 

 main colony. Trautman rightly concluded that it was possible for 

 a cowbird to lay in a solitary nest without discovery and inevitable 

 pursuit, but not in a colony. In Minnesota, Roberts (1932, p. 303) 

 noted that those redwing nests which were built in the marshes 

 usually were not parasitized, whereas those in bushes on uplands 

 near the marshes generally contained cowbird eggs. Although 

 Roberts does not say so specifically, it appears that the nests built 

 in upland bushes were scattered more widely than those in the cattail 

 swamps. In Kent Island, Maryland, during two successive seasons 

 (1958-59), Meanley (in htt.) examined 367 nests and found that five 

 were parasitized. He later wrote me that in his experience, in 

 Maryland and elsewhere, such parasitism invariably occurred in the 

 very earliest redwing nests. The red^vings begin nesting earlier 

 than most of the other passerine birds and the cowbirds begin to lay 

 about the same time as the redwings, but the parasites do not seem to 

 bother the latter when other potential hosts become available. 



At Ithaca, New York, a region where both the redwing and the 

 cowbird are very common and where both species have been exhaus- 

 tively studied (A. A. Allen, 1913b; Friedmann, 1929), many hundreds 

 of nests of the redwing have been examined but none have been 

 found to be parasitized. That some variation may occiu-, even in 

 such areas, is suggested by the observations of Goelitz (1916, p. 147) 

 in lUinois, who writes that, "until this year I have never found eggs 

 of this bird [cowbird] in redwing's nests, but in a little colony of some 

 twenty-five pairs of red-winged blackbirds I destroyed eleven cowbird 

 eggs on June 17, and six on June 27 of the present season." 



Smith (1943, p. 198) studied these blackbirds near Chicago and 

 found that cowbirds seldom molested redwings nesting in sizeable 

 colonies. In 1940 at Orlando, the incidence of parasitism was only 

 0.6 percent (a single case, in which 2 cowbird eggs were laid in an 

 empty redwing nest, resulting in its desertion.) In 1941, no cowbird 

 eggs were found among 563 eggs of redwings. Smith suggested that 

 "there may be an aggregate effect of numbers which retards or even 

 prohibits the deposition of cowbird eggs in redwing populations of 

 high density. In view of the restricted incidence of cowbird parasit- 

 ism and its apparent negligible effect upon redwing mortality, it 

 would appear that this factor is of httle importance in a consideration 

 of the success of redwing reproduction." 



In fm-ther studies in Arkansas as well as in Illinois, the same author 

 (1949, p. 60) found that, out of 653 nests of the redwing, 14 were 

 parasitized, 13 with 1 cowbird egg in each, and 1 with 2 cowbird 



