NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN Jl 



have been cut down ; but they must have been relatively much more 

 common before the region acquired a dense human population. It is 

 possible that isolated clearings in heavy forest were the most important 

 habitat of mixed blue and green tanager and honeycreeper flocks 

 before human interference became appreciable. Many of the social 

 behavior patterns of many species of the blue and green tanager and 

 honeycreeper alliance may have been evolved originally as adaptations 

 to life in mixed flocks that were more like the flocks observed on 

 Barro Colorado Island than any of the other flocks observed in the 

 course of the present study. 



THE MONTANE BUSH FLOCKS 



Montane bush flocks are much less widely distributed in Panama 

 than mixed blue and green tanager and honeycreeper flocks. The 

 montane bush flocks that were studied most intensively during the 

 present investigation are characteristic of the hills and mountains of 

 western Panama and seldom or never occur below 3,000 feet above 

 sea level. 



These flocks were studied on the western slopes of the Volcan de 

 Chiriqui (El Baru), between approximately 4,500 feet and 7,500 feet 

 above sea level (from the town of El Volcan to elevations well above 

 the town of Cerro Punta), during four short periods of observation: 

 between September 17 and September 21, 1958; between March 2 and 

 March 9, 1959; between March 19 and March 30, i960; and between 

 October 3 and October 10, i960. Special attention was paid to the 

 flocks at higher altitudes, above 6,000 feet. 



All or most of the upper slopes of the Volcan de Chiriqui must have 

 been covered by heavy montane forest at one time. Much of the forest 

 of the western slopes has been cut down within fairly recent years, but 

 large patches remain, especially above 6,000 feet. Second-growth 

 forest and scrub are also found in many areas. Most of the observa- 

 tions of mixed flocks were made along the edges of forest and scrub. 



Many of the birds commonly occurring in mixed bush flocks in 

 this region were performing reproductive behavior patterns in March ; 

 but all or most of them appeared to be in the middle of the non- 

 breeding season in September and October. 



THE MOST COMMON SPECIES 



It may be useful to describe the appearance of the most common 

 species of the montane bush alliances in western Panama and sum- 

 marize the most distinctive features of their social behavior apart from 



