HOST RELATIONS OF PARASITIC COWBIRDS 55 



In Colorado, Bendire (1895, p. 307) found "several" parasitized 

 nests; King (1954, pp. 150-154) noted two instances in Whitman 

 County, Washington. In southern Quebec, TerriU (1961, p. 4) 

 found cowbird eggs in 9 out of 146 nests of this flycatcher, a per- 

 centage of 6.2. He felt that the rather late nesting of this bird may 

 have accounted for the low frequency of parasitism. 



In Whitman County, southeastern Washington, an area where the 

 cowbird was not very abundant, King (1955) found that the hatching 

 success of eggs of this flycatcher was very high — 84 percent in 1952, 

 98 percent in 1953. In the latter year, fledging success was 44,6 

 percent. These figures suggest that Traill's flycatcher is a species 

 readily able to survive a considerably greater frequency of cowbird 

 parasitism than our present compilation indicates. 



J. K. Cruttenden (in litt.) writes me that he has a remarkable set 

 of 4 eggs of Traill's flycatcher with one of the brown-headed cowbud, 

 taken in Cook County, lUinois, July 5, 1947. The nest was con- 

 structed in three sections: the cowbird egg was in the lowest section; 

 a new floor had been built over it and in this the flycatcher had laid 

 an egg, and then for some unknown reason she had built another 

 floor, this time over her own egg, and had laid 3 more eggs in the 

 new nest above. Cases of flooring over cowbird eggs, with or without 

 one or more eggs of the host, are weU known for the yeUow warbler 

 and several other birds, but this appears to be the first such instance 

 recorded for this flycatcher. 



Least Flycatcher 

 Empidonax minimus (Baird and Baird) 



The least flycatcher appears to be molested rather seldom by the 

 brown-headed cowbird. I have noted only 19 records in all, distrib- 

 uted from Quebec, New England, New York, Pennsylvania, and 

 Maryland to Michigan, Iowa, Utah, North Dakota, Montana, Alberta, 

 and British Columbia. These records involve two races of the para- 

 site, ater and artemisiae. The old statement in the literature by Baird, 

 Brewer and Ridgway (1874, pp. 154-157) that this is one of the com- 

 monest victims in New England strangely is unsupported by sub- 

 sequent observations, and what records they may have had have 

 similarly not appeared in print. In Michigan, Walkinshaw (1961, p. 

 268) found that this species was victimized less frequently by the 

 parasite than was either the Acadian or Traill's flycatcher. 



Western Flycatcher 



Empidonax difficilis Baird 



Six cases of cowbird parasitism on the western flycatcher have 

 come to my notice, all from California and all concerned with the 



630590—63 5 



