JO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



common occasional member of mixed blue and green tanager and 

 honey creeper flocks, and attendant in relation to the regular members 

 of such flocks. While it is associated with mixed blue and green tana- 

 ger and honeycreeper flocks, however, it sometimes functions as a 

 passive nuclear species for other occasional members of the flocks. 



The blue dacnis is apparently always nuclear and regular. It has 

 not been observed frequently enough to determine if it is a passive 

 nuclear and/or an active nuclear species. 



Most of the remaining species are probably occasional attendant 

 species in mixed blue and green tanager and honeycreeper flocks. Some 

 of them are nuclear, or regular attendants, in other types of mixed 

 flocks ; but their roles in such flocks do not seem to affect their roles 

 in the blue and green tanager and honeycreeper flocks. 



DIFFERENT TYPES OF MIXED FLOCKS 



The frequencies with which blue and green tanager and honey- 

 creeper flocks are formed, and the degree of integration within such 

 flocks, are obviously different in different environments and in the 

 same environment at different times. This may be due partly to the 

 fact that different species are dominant in different environments 

 and/or in the same environment at different times. It was not possible 

 to study this aspect of flock behavior in detail ; but some of the figures 

 in the accompanying tables may help to illustrate some of the varia- 

 tions that can occur. 



Individuals of most species were seen in mixed flocks most fre- 

 quently near Gamboa and near Frijoles in July and August of i960, 

 when blue tanagers were the most common of the tanagers and honey- 

 creepers. Individuals of most species were seen in mixed flocks least 

 frequently near Frijoles between November 1959 and January i960, 

 when crimson-backed tanagers were the most common of the tanagers 

 and honeycreepers. Relatively more birds were seen in tightly inte- 

 grated flocks around the clearing on Barro Colorado Island, where 

 plain-colored tanagers were dominant, than in any of the other areas. 



It seems likely that most of the birds of the blue and green tanager 

 and honeycreeper alliance around the clearing on Barro Colorado 

 Island were very much habituated to one another. They were confined 

 to a relatively small area, separated from the nearest similar areas by 

 large expanses of heavy forest and/or the waters of Gatun Lake, and 

 tended to encounter one another again and again. 



Environments like the clearing on Barro Colorado Island are rare 

 in central Panama now, as most of the heavy forests of this region 



