116 U.S. NATIONAL MUSEUM BULLETIN 23 3 



or, to put it in other words, one out of every four pairs of Kentucky- 

 warblers seemed to have lost 1 egg from its normal clutch. In addi- 

 tion, some of the warbler eggs left in the nests were rendered losses 

 because of shell punctures, which resembled claw or bill marks. 

 Further, a fair number of nests were found deserted even before they 

 were finished; other deserted nests may have contained 1 or 2 eggs, 

 and some of these nests may have contained cowbu'd eggs, whose 

 presence may have been related to their desertion. Jacobs concluded 

 that, while the Kentucky warbler suffered heavily, the second broods 

 were usually less heavily victimized by the cowbird than were the 

 earlier ones. 



Mourning Warbler 



Oporornis Philadelphia (Wilson) 



The mourning warbler is a fairly frequent victim of the brown- 

 headed cowbird in a few places, but generally it must be rated an 

 uncommonly utilized host. Two parasite races are involved: arte- 

 misiae in an instance reported from Garland, Manitoba, by Godfrey 

 (1953, p. 45); ater in 19 cases ranging from Quebec (Lloyd, 1949) 

 and Ontario in Canada to New York, Michigan, Illinois (Pitelka, 

 1939), Wisconsin, and Minnesota (Chambers, 1947; Cox, 1958, 1960; 

 Hickey et al., 1955) in the United States. 



Near Montreal, Quebec, L. M. Terrill (1916, p. 8) reported that, 

 of 25 nests of this warbler, 8, or 32 percent, contained eggs or young 

 of the brown-headed cowbird. These figiu-es indicate that, although 

 the mourning warbler may be relatively unimportant in the economy 

 of the parasite, the latter, in that area at least, may be a fairly serious 

 factor in the numerical status of the former. 



A record for the eastern race of the parasite by Black (1955, p. 23), 

 who observed adult hosts feeding two of their own young and one 

 young cowbird in Macomb County, Michigan, on June 26, is of 

 interest because it shows that the presence of the parasite did not 

 prevent the birds from rearing their own young along with it. 



At Ithaca, New York, A. A. Allen found a recently fledged cow- 

 bird attended by a mourning warbler. Robbins (1947) reported two 

 parasitized nests in Oconto County, Wisconsin, found in 1947 by 

 Carl Richter. 



Devitt (1944, p. 83) reported a nest with 2 eggs of the warbler and 

 1 of the cowbird at Minesing, Ontario, on June 9, 1929. Dr. Paul 

 Harrington informed me that on that same date he found a parasitized 

 nest near Wasaga Beach, South Georgian Bay, Ontario. Other cases 

 are represented by parasitized sets of eggs in the R. M. Barnes col- 

 lection, now in the Chicago Natural History Museum, and the J. H. 

 Bowles collection, now dispersed. 



