IIO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



with their social reactions apart from mixed flocks in much the same 

 way as the corresponding reactions of most of the nuclear species of 

 blue and green tanager and honey creeper flocks and some of the 

 nuclear species of mixed montane bush flocks. Variable seedeaters 

 resemble such passive nuclear birds as plain-colored tanagers and 

 brown-capped bush-tanagers in showing a high degree of intraspecific 

 gregariousness ; while blue-black grassquits resemble such active nu- 

 clear birds as palm tanagers and green honeycreepers in being only 

 slightly gregarious among themselves apart from mixed flocks. 



The members of all the mixed flocks of small finches in central 

 Panama usually feed on the same or similar food and tend to remain 

 at approximately the same level (on or near the ground) most of the 

 time they are together. It is probably significant, therefore, that inter- 

 specific supplanting attacks are common in such flocks. In flocks 

 composed of variable seedeaters and blue-black grassquits alone, the 

 variable seedeaters frequently supplant blue-black grassquits, but 

 blue-black grassquits seldom or never supplant variable seedeaters. 



MIXED FLOCKS ON CERRO CAMPANA 



Cerro Campana is an isolated mountain, west of the Canal Zone 

 in central Panama, which reaches an altitude of approximately 3,300 

 feet above sea level. Part of the upper slopes of this mountain are 

 covered by heavy montane forest, most of which seems to be mature. 

 The bird fauna of the montane forest on Cerro Campana above ap- 

 proximately 2,000 feet includes a number of species that appear to be 

 relicts in central Panama. Several montane species that occur on 

 both Cerro Campana and the Volcan de Chiriqui are found at much 

 lower altitudes on the former mountain than on the latter. Such 

 species may have been marooned on Cerro Campana at the end of the 

 last cold period of the Pleistocene, and have become adapted to a 

 warmer climate. 



Many tanagers and related species occur on the upper slopes of 

 Cerro Campana. Some of these species associate with one another to 

 form mixed flocks, the most conspicuous of which occur in the tree- 

 tops and along the edges of the montane forests, usually quite high 

 above the ground. These flocks are usually composed of silver- 

 throated tanagers, bay-headed tanagers, and/or tawny-capped 

 euphonias (Tanagra anneae). Birds of other species also occur in 

 such flocks, but seemingly relatively less frequently. Among the other 

 birds I have seen associated with the mixed flocks of the montane 

 forests of Cerro Campana are blue tanagers, green honeycreepers, 



