HOST RELATIONS OF PARASITIC COWBIRDS 81 



M.a. artemisiae] the others, to the typical subspecies M.a. ater. The 

 fact that the waxwing is a late breeding bird and that usually it does 

 not begin to nest until the laying season of the cowbird is well past its 

 height probably explains its relative immunity from the attentions of 

 the parasite. Over a period of 50 years in southern Quebec, Terrill 

 (1961, p. 5) found 329 waxwing nests, of which only 4 had been para- 

 sitized by the cowbnd. 



One new item of information about this uncommon victim of the 

 brown-headed cowbird has been brought to light recently by Nickell 

 (1955, pp. 91-92). He points out that the waxwing, unlike many birds, 

 begins to incubate after the laying of the fh'st egg and that, as a result, 

 the eggs may hatch at intervals rather than all together. Nickell 

 found a nest with 2 young waxwings about four or five days old and 2 

 young cowbu'ds — one about six days old, the other three days old — 

 plus 1 waxwing egg. He attributes the early hatching of the older 

 cowbird to this peculiar mode of incubation. 



This fact leads to the following consideration. In the majority of 

 cases, cowbird eggs are laid in nests already containing eggs of the 

 hosts and, in many cases, the cowbird eggs develop slightly more 

 rapidly than do their nest-mates, giving them the advantage of earlier 

 hatching. It would appear, therefore, that, in a species with the 

 incubation habits of the waxwing, such a pattern might offset the 

 parasite's advantage — or at least make it more likely that one or more 

 of the host's young would survive with it and compete with it. 



Phainopepla 



Phainopepla nitens (Swainson) 



This bird has been reported only twice as a victim of the dwarf race 

 of the brown-headed cowbird. Strong (1919, p. 181) reported a 

 phainopepla's nest containing 1 egg of the parasite which was found 

 by Frederick Dunham at Tucson, Ai-izona, on May 20, 1897. Rowley 

 (1930, pp. 130-131) recorded a nest containing a young cowbird as 

 well as a young phainopepla on June 2, 1929, near Alhambra, southern 

 California. "The cowbird actually was forcing the young 'Pep' from 

 his rightful cradle, and the adults were simply gorging the hoggish 

 young cowbu'd with all the food it could hold, seemingly forgetting 

 about their own 'child' that was ... in the bottom of the over- 

 crowded nest." Both records refer to the subspecies lepida of the host. 



Starling 



Sturnus vulgaris Linnaeus 



The hole-nesting habits and the pugnacious disposition of the 

 starling probably are the reasons for its being molested very seldom 

 by cowbirds. Only two records of parasitism on this introduced 



