30 U.S. NATIONAL MUSEUM BULLETIN 233 



place). The observers found that the persistent repetition of this 

 display often evoked preening behavior from a variety of birds, 

 including redwinged blackbirds, meadowlarks, house sparrows, and 

 shell parakeets (m captivity). Some birds, such as the common and 

 great-tailed grackles, the inca and mourning doves, did not respond 

 to the invitation to preen the cowbu'ds. Invitation to preening be- 

 tween cowbirds themselves is uncommon, and it appears to have no 

 place in the provocation of interspecific preening. This display is 

 given by adults and by birds of the year, by males and by females. 

 The extent to which preening may go is sometimes surprising. 

 Baird in Rhode Island and Behrendt (1960) in New York are cited by 

 Selander and La Rue as having noted cases wherein invited house 

 sparrows actually hopped onto the backs of the inviting cowbirds in 

 order to preen them more effectively. 



The authors suggest that the interspecific preenmg invitational 

 display may be an adaptation for brood parasitism. This suggestion 

 is based on the assumption that such behavior may lessen the possible 

 hostile reactions of potential hosts to their would-be parasites. There 

 is no evidence, however, to indicate that a female cowbird, about to 

 lay in a nest, makes any effort to establish contact with its potential 

 victim. It usually(?) enters the nest while the owner is away, lays 

 its eggs as quicldy as possible and leaves thereafter. Moreover, the 

 invitation to preen is not given only, or even chiefly, to species that 

 are frequently parasitized. 



It is not clear what advantage could accrue to the cowbirds if, as 

 adults, they became more acceptable to even the more frequently 

 imposed upon species of their hosts. Such advantage appears un- 

 necessary since there is evidence of hostility toward them on the part 

 of only a small number of their victims (see pp. 33-34). In most cases 

 there seems to be little need for greater acceptability, especially since 

 the social contacts are short and relatively infrequent. Even in 

 species wherein hostility to adult cowbirds is not noticeable (or, at 

 least, has not been noticed), the individuals are apt to show excitement, 

 possibly of an aggi'essive nature, when mtruders come to their nests. 

 Although it seems questionable whether or not there is any meas- 

 urable advantage to the intruders to have had earlier preening associa- 

 tion with the intended victims, this possibility cannot be ruled out 

 arbitrarily: even slight differences of response in short and infrequent 

 contacts may at times be critical. 



In the light of present Imowledge, it is not too safe to evaluate such 

 behavior. It seems more in accord with the total evidence to interpret 

 this relative ease with which cowbirds solicit preening from other 

 birds as a result of brood parasitism, as a possible "memory induced" 

 reaction based on early experience of care by adults of other species. 



