NO. 7 FLOCKS OF NEOTROPICAL BIRDS MOYNIHAN 79 



species are even more strikingly similar than their interspecific rela- 

 tions. 



Brown-capped bush-tanagers are highly gregarious among them- 

 selves in almost exactly the same way as plain-colored tanagers. Dur- 

 ing the nonbreeding season most brown-capped bush-tanagers tend to 

 associate with one another in rather stable groups of 4 to 8 or 10 

 individuals. Many or most of these groups appear to be composed of 

 more than one family (i.e., parents and one brood of young). Indi- 

 vidual birds, pairs, and family groups are seldom territorial during 

 the nonbreeding season, or, at least, seldom defend territories for any 

 appreciable continuous length of time. Some individuals, apparently 

 adult males, may show indications of territorial defense for a few 

 minutes, especially very early in the morning and late in the after- 

 noon during the nonbreeding season, but such behavior is apparently 

 always very brief at this season. During the breeding season, the 

 larger groups of brown-capped bush-tanagers tend to break up. Pairs 

 and apparently unmated single birds separate comparatively frequently 

 and remain on individual territories for comparatively long periods of 

 time. They usually spend most of the mornings, at least, on their own 

 territories, but large groups are still re-formed occasionally, especially 

 in the afternoons. I have seen flocks of brown-capped bush-tanagers 

 during the later part of the courtship phase of the breeding season 

 that were quite as large as any flocks of the same species observed 

 during the nonbreeding season. 



This high degree of intraspecific gregariousness is correlated with 

 the usual types of movements and calls. Brown-capped bush-tanagers 

 are very restless, almost constantly active, moving from bush to bush 

 and tree to tree with very great rapidity. They are also very noisy 

 (see comments below, in the discussion of the sooty-capped bush- 

 tanager). They frequently perform exaggerated wing-flicking and 

 tail-flicking movements, very much like the corresponding movements 

 of plain-colored tanagers. They also utter many loud and hard call 

 notes and rattling calls which are almost equally reminiscent of the 

 most common calls of plain-colored tanagers. Some of these similari- 

 ties between the two species are probably due to convergence, as there 

 are indications that the genera Chlorospingus and Tangara are not 

 very closely related to one another. Chlorospingus is probably more 

 closely related to some of the bush-finches and/or the Ramphocelus 

 tanagers, while Tangara is probably more closely related to some of 

 the tanagers usually included in the genus Thraupis; and neither 



