HOST RELATIONS OF PARASITIC COWBIRDS 27 



summer. At this time many may lay together in old deserted nests, 

 as many as 13 hens using the same nest and as many as 30 or 35 eggs 

 being deposited in single nests. In these cases, the laying birds do not 

 remove eggs from the nests. It looks as though egg removal in this 

 species is an adult habit, not one found in subadult (year-old) birds. 

 The fact that the nests used are deserted ones may have something to 

 do mth this, but more data are needed to clarify the situation. 



The lack of egg removal, however, in the screaming cowbird and in 

 its evolutionary descendant, the red-eyed cowbird, makes it possible 

 to conclude that this habit is not an essential portion of a proprietary 

 interest in a host nest although it is closely associated with such an 

 interest. In the brown-headed cowbu'd egg removal is one manifes- 

 tation of interest in the nest, one that becomes more readily interpreted 

 if it is connected with a continued and proprietary interest. 



While the cowbu'd may have an interest of some duration m some 

 of the nests it has parasitized, this usually terminates long before the 

 eggs hatch. Ordinarily, it shows no interest in the subsequent fate 

 of the nest, eggs, or young, but there are in prmt a few observations 

 of attention paid by female cowbu'ds to young of theh- own species. 

 Bonwell (1895, p. 153) reported seeing a hen cowbird feeding a j^oung 

 one in a rose-breasted grosbeak's nest. "Nearly every evenmg she 

 would come and feed the young cowbird, but if the young grosbeaks 

 would open their mouths for food, she would peck them on the head 

 and refuse them food. . . ." This account implies gi'eater discrimina- 

 tion on the part of the cowbuxl than of the gi'osbeak, which seems 

 highly unlikely. The whole incident reads as if it were "improved 

 upon" by subsequent recollections, and, on the whole, it seems too 

 far from the plain, unembellished record to be acceptable, and it may 

 well be ignored. However, Forbush (1927, pp. 424-425) mentioned 

 two other cases. He cited Al. A. Walton's experience (1903, pp. 211- 

 214) with a hen cowbu'd "which, as he believed, visited from time to 

 time the nest in which her egg was laid, and finally fed and cared for 

 her yoimg one . . . ." From his acquaintance with Mr. Walton, 

 Forbush was "inclined to believe that his observations were reported 

 accurately, but that his deductions from those observations often 

 were unwarranted by the facts. He 'believed' that this Cowbird 

 made frequent visits to the 'Yellow Bird's' nest in which her egg was 

 deposited but did not say that he saw this. However, he wi'ote that 

 he saw her feeding her own young and assisting the male 'Yellow Bird ' 

 in feeding it, but he had no way of identifying the feeding Cowbu'd 

 with the bird that laid the egg and no way of proving that the bu'd 

 doing the feeding at different times was always the same individual." 



To date, Walton's observations have remained unique, but they do 

 establish that, in at least one instance, a brown-headed cowbu'd did 



