44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



gregariousness. 7 More important, perhaps, is the fact that the three 

 species that join and follow plain-colored tanagers most frequently 

 and persistently, i.e., the palm tanager, blue tanager, and green honey- 

 creeper, are much larger and/or much more aggressive and able 

 fighters than plain-colored tanagers. They may intimidate plain- 

 colored tanagers sufficiently strongly to suppress any overt expressions 

 of aggressiveness by the latter, even when the latter are irritated 

 by their presence. 



It might be supposed, therefore, that the other species in mixed blue 

 and green tanager and honeycreeper flocks were essentially parasitic 

 on the plain-colored tanagers. Whatever the advantages of forming 

 mixed flocks may be (see below), all or most of these advantages 

 might be obtained by the other species and not the plain-colored 

 tanagers. 



This may be true in some cases, but not in all. Two types of evi- 

 dence would suggest that plain-colored tanagers must also derive 

 some advantage, at least sometimes, from their associations with 

 individuals of other species. 



The most convincing evidence in this connection is the plumage of 

 the plain-colored tanager. It is very much duller than that of any other 

 species of the genus Tangara. This dullness may be considered a type 

 of neutral coloration, and seems to be an adaptation to facilitate asso- 

 ciations between plain-colored tanagers and individuals of other spe- 

 cies. The neutral coloration of the plain-colored tanager has already 

 been discussed in an earlier paper (Moynihan, op. cit.). Part of this 

 discussion may be quoted here : 



The dull coloration of the Plain-colored Tanager would seem to be a specific 

 adaptation to help the species play its role in . . . mixed flocks. It seems to be 

 effective just because of its dullness, its neutral quality. If the Plain-colored 

 Tanager were more conspicuously colored, it might be less attractive to, or exert 

 less influence upon, its associates of other species . . . The drab appearance of 

 the Plain-colored Tanager probably makes it look less different to its brightly 

 colored associates than it would if it had a distinctive bright pattern of its own. 

 Of course, the Plain-colored Tanager might be even more effective in attracting 

 other species if it could develop the same conspicuous colors and patterns as 

 theirs; but most of the species with which it associates are so different from 

 one another that it would be very difficult or impossible to mimic them all. The 

 Plain-colored Tanager seems to have evolved a "compromise" type of coloration 



7 Observation of captive plain-colored tanagers and golden-masked tanagers 

 under identical conditions would suggest that both the attack and escape drives 

 of the very gregarious plain-colored tanagers are weaker, or less easily aroused, 

 than the corresponding drives of the closely related but less gregarious golden- 

 masked tanagers. 



