52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



to approach (or try to approach) individuals of other species more 

 often than they are approached by individuals of other species. In 

 one way the social role of green honeycreepers is even more unbal- 

 anced than that of palm tanagers ; they do not seem to be as attractive 

 to any other species as palm and blue tanagers are to one another. 

 In another way the social role of green honeycreepers in mixed flocks 

 is more obviously ambivalent than that of any other common species 

 of the blue and green tanager and honeycreeper alliance. Green honey- 

 creepers frequently try to approach individuals of other species in an 

 apparently nonhostile or "friendly" manner; but they also tend to be 

 very aggressive toward individuals of other species. They are proba- 

 bly more often openly aggressive toward individuals of other species 

 than are any other regular members of the mixed blue and green tana- 

 ger and honeycreeper flocks. 



This ambivalent behavior of green honeycreepers in mixed flocks 

 seems to be a reflection of their behavior to one another (see Moyni- 

 han, i960). There are indications that they are strongly attracted 

 to one another by some sort of gregarious or general social impulse ; 

 but they seldom or never occur in stable unmixed flocks of their own 

 species alone. This is largely owing to the fact that whenever two 

 unrelated green honeycreepers (i.e., birds that are not members of the 

 same pair or family group) come together, they almost always start 

 to dispute vigorously with one another. Sooner or later (usually 

 sooner) one bird will attack the other and drive it away. 



It is quite possible that the reactions of green honeycreepers to 

 individuals of many other species are produced by the same tendencies 

 or internal drives as their reactions to one another ; but the two types 

 of reactions seldom take exactly the same form, i.e., they seldom 

 include exactly the same movements, postures, or calls, in exactly the 

 same sequence. Such differences may be due to several factors. It is 

 obvious, for instance, that green honeycreepers seldom respond as 

 strongly to individuals of other species as to other members of their 

 own species, even when the quality of the response is the same in both 

 cases. It is also evident that the social reactions of green honey- 

 creepers are greatly affected by several aspects of the social environ- 

 ments in which they occur. Green honeycreepers may perform differ- 

 ent acts, or (at least) the same acts with different frequencies, in 

 different social environments, even when their internal motivation is 

 the same in the different environments. This is also characteristic of 

 the behavior of birds of all species ; but it is often particularly con- 

 spicuous in the case of green honeycreepers in mixed flocks. 



