NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 53 



It is possible to recognize certain relatively minor subdivisions or 

 subgroups, special associations of a few species, within the larger 

 group of the blue and green tanager and honeycreeper alliance as a 

 whole. These subgroups are not very distinct and never exclusive; 

 but some species, including the green honeycreeper, behave slightly 

 differently in different subgroups. 



Different types of subgroups may be recognized by the use of dif- 

 ferent criteria. Perhaps the most easily distinguished are two sub- 

 groups that may be called predominantly tanager flocks and pre- 

 dominantly honeycreeper flocks. The former are largely composed of 

 tanagers, especially plain-colored, palm, and blue tanagers, and include 

 relatively few honeycreepers ; while the latter are largely composed of 

 honeycreepers, sometimes accompanied by many warblers (see below), 

 and include relatively few tanagers. 



Green honeycreepers differ from the other common honeycreepers 

 of central Panama in being associated with predominantly tanager 

 flocks almost as frequently as with predominantly honeycreeper flocks. 



In predominantly tanager flocks, their most conspicuous social reac- 

 tions are attempts to join and follow individuals of other species. 

 They seem to be much more strongly attracted to plain-colored tana- 

 gers than to any other species of tanager. They join and follow plain- 

 colored tanagers relatively more frequently than they do individuals 

 of any other common species of the blue and green tanager and honey- 

 creeper alliance ; and they occur with plain-colored tanagers in mixed 

 flocks of only two species relatively much more frequently than with 

 individuals of any other species of tanager. Their responsiveness to 

 plain-colored tanagers seems to be a special interspecific preference, 

 essentially similar to the corresponding preferences of such species 

 as the palm tanager and the blue tanager. 



The vocal patterns of the green honeycreepers may be significant in 

 this connection. They frequently utter sharp call notes and rattling 

 calls that are distinctly different in sound from any of the common 

 vocal patterns of the red-legged blue honeycreeper and the blue dacnis, 

 but very similar to the most common vocal patterns of the plain- 

 colored tanager and the golden-masked tanager. Observation of cap- 

 tive birds would suggest that green honeycreepers are strongly 

 attracted by the sound of the calls and notes of plain-colored tanagers 

 and golden-masked tanagers that are most like their own calls and 

 notes. There is also some evidence that the vocal repertory of the 

 green honeycreeper is rather specialized, more so than the correspond- 

 ing repertories of the red-legged blue honeycreeper and the blue dacnis. 



