NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 6l 



The crimson-backed tanager is not quite a regular member of the 

 mixed blue and green tanager and honeycreeper flocks in this sense. 



Crimson-backed tanagers do occur in mixed flocks with blue and 

 green tanagers and honeycreepers — so frequently, in fact, that they 

 may be considered members of the blue and green tanager and honey- 

 creeper alliance (see definition above). They also join, follow, and/or 

 supplant regular members of the blue and green tanager and honey- 

 creeper flocks occasionally, and are occasionally joined, followed, 

 and/or supplanted by regular members of these flocks. Such clear-cut 

 reactions are relatively rare, however. Crimson-backed tanagers are 

 usually joined and followed by other members of the blue and green 

 tanager and honeycreeper alliance even less frequently than are red- 

 legged blue honeycreepers in similar social situations. Crimson-backed 

 tanagers often appear to be purely casual associates of mixed blue 

 and green tanager and honeycreeper flocks, keeping some distance 

 away from all or most of the other members of such flocks, and 

 frequently moving in different directions from the other members of 

 the flocks. Even more significantly, crimson-backed tanagers also 

 prefer to associate with some other species that are not members of 

 the blue and green tanager and honeycreeper alliance (see below). 



The fact that both the plumage and the most common notes of crim- 

 son-backed tanagers (see above) are very conspicuously different 

 from the corresponding characters of any regular member of the blue 

 and green tanager and honeycreeper flocks is probably a definite hin- 

 drance to more frequent and closer associations between crimson- 

 backed tanagers and most other members of the blue and green tanager 

 and honeycreeper alliance. Crimson-backed tanagers must stimulate 

 the generalized gregariousness of many or all the other members of 

 this alliance; but they probably do so less strongly than they would 

 i f their appearance and notes were less distinctive. 



It is also possible, since crimson-backed tanagers are comparatively 

 large birds, that they tend to alarm the smaller blue and green tanagers 

 and honeycreepers rather strongly. 



There is no evidence, however, that any of the other members of 

 the blue and green tanager and honeycreeper alliance have developed 

 a definite aversion to crimson-backed tanagers, as they seem to have 

 to some related species (see below). 



Blue tanagers tend to associate with crimson-backed tanagers some- 

 what more frequently and/or more closely than do all or most of the 

 other members of the blue and green tanager and honeycreeper alli- 

 ance. This may be due to the fact that blue tanagers and crimson- 



