HOST RELATIONS OF PARASITIC COWBIRDS 51 



found a cowbird's egg in a nest of this flycatcher in Ciiaiies County, 

 Maryland; Stewart and Robbins (1958, p. 329) mention two instances 

 in Maryland, one of which is the E. J. Court record mentioned above; 

 A. J. Berger (1960, p. 118) examined 11 nests near Ann Arbor, Mich- 

 igan, during four summers of 1956-1959 and found that one of them 

 was "parasitized" five days after it had been deserted. This nest was 

 in one of a series of nesting boxes placed by Berger for the flycatchers. 

 When using this type of box, the flycatchers would cover the entire 

 floor with nesting material to the depth of an inch but would make 

 the nest cup for the eggs at the rear of the box. The parsite did not 

 lay her egg in the nest cup but on the nesting material halfway back 

 from the entrance hole. Since the nest had been deserted by the time 

 the cowbird layed in it, one may ask whether, in a strict sense, this is 

 really an instance of parasitism on the crested flycatcher. 



In all the above cases the race boreus of the host and the nominate 

 race of the parasite are involved. 



Eastern Phoebe 



Sayornis phoebe (Latham) 



The eastern phoebe is a very common victim of the brown-headed 

 cowbird. Over 375 records have come to my attention, reports that 

 range from Quebec, Massachusetts, Connecticut, New York, New 

 Jersey, Pennsylvania, Delaware, Maryland, and Virginia westward 

 through Ontario, Manitoba, Saskatchewan, to Alberta; through 

 West Virginia, Ohio, Indiana, Illinois, Michigan, Wisconsin, into 

 Minnesota, Iowa, and Kansas. The records from Minnesota, Sas- 

 katchewan, and Alberta refer to the northwestern race of the cowbird, 

 M.a. artemisiae; the others, to the nominate subspecies, M.a. ater. 

 The degree to which the phoebe is affected varies locally. At Ithaca, 

 New York, in my own field experience, out of 22 nests found, 16, or 

 75 percent of the nests, contained from 1 to 3 eggs apiece of the 

 cowbird. At Amboy, Illinois, Blocker (1936, p. 133) reported 50 

 percent of the phoebes' nests had cowbirds' eggs in them. In southern 

 Quebec, in TerriU's experience (1961, p. 3) the percentage of para- 

 sitism was 26 percent, out of 100 nests; in the neighborhood of Buckeye 

 Lake, Ohio, Trautman (1940, p. 393) found that 9 out of 134 nests, or 

 only 7 percent, were parasitized. In Kansas, Johnston (in litt.) 

 informed me that 8 out of 79 phoebe nests, or rough tly 10 percent, 

 were parasitized. In the Ithaca area, the first cowbird eggs of the 

 season were found usually in phoebes' nests, and, until other species 

 began nesting in numbers, this flycatcher was the chief host of the 

 parasite. Later in the breeding season it was less frequently para- 

 sitized than it had been earlier. In southern Quebec, Terrill also 

 noted that "early in the season, nests of the Phoebe may be the only 



