NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 59 



lowed, and supplanted by individuals of other species more frequently 

 than they themselves join, follow, and supplant ; but they are joined 

 and followed relatively much less frequently than are plain-colored 

 tanagers, and are also relatively much less common than plain-colored 

 tanagers in obviously tightly integrated mixed flocks and in flocks 

 composed of only two species. They do not seem to be particularly 

 attractive to any species of tanager. With the possible exception of 

 blue dacnises (see below), no other honeycreepers seem to behave as 

 if they had a strong "friendly" interspecific preference for red-legged 

 blue honeycreepers under natural conditions. I have never seen a 

 female shining honeycreeper react to a male red-legged blue honey- 

 creeper as a potential mate under natural conditions. 



It is obvious, nevertheless, that the noisiness and rapid movements 

 of red-legged blue honeycreepers greatly increase the conspicuousness 

 of the mixed flocks in which they occur and probably, therefore, 

 increase the attractiveness of such flocks to many birds of many 

 species. It is my impression that mixed flocks that include red-legged 

 blue honeycreepers tend to attract more birds of other species than 

 otherwise identical flocks that do not include red-legged blue honey- 

 creepers. In particular, migrant warblers of many species seem to be 

 more likely to join mixed flocks that include red-legged blue honey- 

 creepers than all or most other mixed flocks in the same environments. 

 I am not sure of the precise social relationships between most of these 

 warblers and red-legged blue honeycreepers. It seems unlikely that 

 any of these warblers have any special interspecific preference for red- 

 legged blue honeycreepers. 



Red-legged blue honeycreepers may attract individuals of many 

 other species as frequently as is possible by stimulating generalized 

 gregariousness alone. Their social role in many mixed flocks is 

 probably very similar to what the social role of plain-colored tanagers 

 would be if plain-colored tanagers did not stimulate the "friendly" 

 special interspecific preferences of some other species so strongly. 



The fact that red-legged blue honeycreepers do not evoke as many 

 nonhostile interspecific preferences as plain-colored tanagers may 

 be due largely to the distinctive nature of some of their most common 

 vocal patterns, which are quite different from the corresponding 

 patterns of any other species of the blue and green tanager and 

 honeycreeper alliance in central Panama, and the bright and intri- 

 cately patterned nuptial plumage of the males. Such characters are 

 presumably advantageous because they help to maintain the reproduc- 

 tive isolation of the species. They may also tend to promote other 

 types of social isolation as well. 



