2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



maintenance of certain types of mixed species flocks. It also includes 

 some suggestions about the probable course of evolution of such flocks. 

 Most of the observations were made in Panama between September 

 1957 and November i960. Special attention was paid to mixed flocks 

 of finches, tanagers, honeycreepers, and warblers. Several different 

 types of mixed flocks of these birds are common in different habitats 

 in Panama. The two that were studied most intensively may be called 

 the "blue and green tanager and honeycreeper flocks" and the "mon- 

 tane bush flocks." These are terms of convenience. Flocks of the 

 first type frequently include other species in addition to blue and 

 green tanagers and honeycreepers. Flocks of the second type are not 

 confined to bushy habitats. 



Mixed blue and green tanager and honeycreeper flocks were ob- 

 served, off and on, throughout the whole period of this study. Other 

 types of mixed flocks were observed much more briefly (see below). 



THE BLUE AND GREEN TANAGER AND 

 HONEYCREEPER FLOCKS 



DESCRIPTION OF THE MOST COMMON SPECIES 



Before proceeding to discuss these flocks, it may be helpful to 

 describe the appearance of some of the species involved and to say 

 something of their behavior apart from mixed flocks in central 

 Panama. This will be partly a recapitulation of data included in other 

 publications (e.g., Skutch, 1954; Sturgis, 1928; and Moynihan, op. 

 cit). 



Plain-colored Tanager (Tangara inornata). 1 — A comparatively 

 small tanager. Sexes nearly identical in plumage: largely dull gray, 

 with black wings and tail and bright blue patches on the upper wing 

 coverts. 



Resident in Panama. Most common along the edges of fairly 

 mature forest but occurring also in young second-growth forest. 

 Primarily a bird of the treetops. 



Very gregarious apart from mixed species flocks. Very restless 

 and active. Very noisy, frequently uttering loud and sharp tsit call 

 notes, which may be accelerated to produce mechanical-sounding 

 rattles. 



Palm Tanager ( Thraapis palmarum) . — A moderately large tanager. 

 Sexes nearly identical in plumage : dull olive-green, with black wings 

 and tail. 



1 The scientific names of all the Panamanian species cited in this paper follow 

 Eisenmann, 1952 and 1955. 



