HOST RELATIONS OF PARASITIC COWBIRDS 29 



tive aggression against nests is something that has been noted in the 

 case of captive female (and male) cowbirds when a nest was placed 

 in the cage as a laying inducement. Certainly, in the case of the 

 captive birds, there were no cowbird eggs involved and thus no possi- 

 ble question of parentage or of continuing interest in the nest. 



Quite apart from an interest of shorter or longer duration in specific 

 nests is the fact that very occasionally the brown-headed cowbird 

 may reveal some nest-building atavisms. Lasky (1950, p. 160) 

 twice noted a courting male bird "toying with a dead leaf or a piece 

 of debris while bowing to a female," a residual "symbolic" nest- 

 building act comparable to similar behavior in some self-breeding 

 birds. There are m the literature two older statements involving 

 much more than symbolic tokens of an earlier nest-building behavior. 

 Although they are so contrary to the experience of all other observers 

 as to seem doubtful, they should be mentioned here. Swain (1899) 

 saw a pair of cowbu'ds carrying nesting material to a hole under the 

 eaves of an old building. He noticed them doing this day after day 

 for an unspecified number of days, but they disappeared soon after- 

 ward and made no attempt to use the nest structure. Here it is 

 possible that there may have been a misidentification of the birds 

 although this cannot be proved. The question of correct identification 

 seems not to be mvolved in Honecker's (1902) statement, which is 

 even more difficult to reconcile with what we know of the cowbirds. 

 He kept a pair of these birds in a large cage and he wi'ote that the 

 female built a nest in which she laid 4 eggs, incubated them, and 

 reared all four young birds! Not only has no one else had this experi- 

 ence, but in recent years a number of investigators have been keeping 

 cowbirds in aviaries, deliberately designed with facilities and conditions 

 to induce breeding, and none of the mvestigators have had any such 

 response. In fact, the most that any of them have reported is that 

 occasional mdividual hens laj^ed a few eggs in old nests supplied them 

 as "mducers," but m no case did a cowbird attempt to incubate. 

 In some cases, the only interest the cowbirds showed in the old nests 

 was to tear them to pieces or to toss out of them any eggs, real or 

 false, that had been placed in them to increase their possible suggestive 

 value. An earl}^ instance of this adverse interest in nests by captive 

 cowbirds was that reported in 1926 by Luttringer. 



Interspecific Preening Invitational Behavior 



Selander and La Rue (1961) recently have shown that brown -headed 

 and bronzed cowbirds approach individuals of other bird species and 

 solicit preening from them. The cowbirds do this by giving a special 

 display which involves bowing their heads and ruffling somewhat the 

 feathers on the back of their necks (where much of the preening takes 



