NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 127 



of southeastern Brazil, Misiones, and eastern Paraguay. Mitchell 

 also cites a number of other species as more or less frequent asso- 

 ciates of the green-headed tanager in mixed flocks, including the 

 red-necked tanager, Spix's scarlet-crested tanager (Tachyphonus 

 cristatus), the rufous-headed tanager (Hemithraupis ruficapilla) , the 

 yellow-headed tanager (H. flavicollis) , 21 the bananaquit, and the blue 

 dacnis. Mitchell's description would imply that all or most of these 

 species are usually or always active nuclear or attendant species in 

 these flocks. They are all much more widely distributed than the 

 green-headed tanager. 



Slud (i960) has described certain aspects of some mixed flocks 

 that occur in lowland forest and scrub in northeastern Costa Rica, in 

 an area that is more humid, or more consistently humid, than most 

 of central Panama. Some of these Costa Rican flocks are largely or 

 completely composed of tanagers, honeycreepers, and/or finches. Slud 

 cites three species of tanagers and one species of finch that are 

 rare or absent in central Panama but are common and tend to 

 play nuclear roles in mixed flocks in Costa Rica. These species are 

 the black- faced grosbeak (Caryothraustes poliogaster), the olive tana- 

 ger {Chlorothraupis carmioli), the tawny-crested tanager {Tachy- 

 phonus delatrii), and the great shrike-tanager (Lanio aurantius) . 22 

 The first three species show a high degree of intraspecific gregarious- 

 ness and seem to play passive nuclear roles in all or most of the mixed 

 flocks with which they are associated. Their social behavior would 

 thus appear to be essentially identical with that of plain-colored tana- 

 gers in central Panama. Great shrike-tanagers are not highly 

 gregarious among themselves, but also seem to play a passive nuclear 

 role in mixed flocks. All four of these passive nuclear species have 

 comparatively restricted ranges. The black- faced grosbeak extends 

 from southeastern Mexico to central Panama. The olive tanager 

 extends from eastern Nicaragua to eastern Panama, and has an 

 isolated population in part of tropical Peru. The tawny-crested 

 tanager extends from eastern Nicaragua to western Ecuador. The 

 great shrike-tanager extends from southeastern Mexico to western 

 Panama. It will be noticed that none of these species is widely 

 distributed in the Amazonian region of South America. The ranges 

 of these species cannot, unfortunately, be compared with those 



21 The Latin names of these purely South American species follow Pinto 

 (1944). The English vernacular names are those used by Mitchell. 



22 Both the scientific and vernacular names of these species follow Eisenmann, 

 1955- 



