NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 45 



instead, one that is moderately different from those of almost all its associates, 

 without being too conspicuously different from any. The fact that the com- 

 promise, neutral, coloration is drab may also have another advantage. It may 

 make the other signal patterns of the species, the restlessness, calling, flash 

 patterns of wings and tail, and flicking movements, relatively more effective 

 than they would be otherwise. The drabness may allow the other characters to 

 attract and hold a greater share of the attention of observers. 



In other words, the attractiveness of plain-colored tanagers is 

 partly a direct result of their behavior; but their behavior can only 

 produce its full effect because their plumage is neutral, and their 

 neutral plumage has probably been evolved as a special adaptation to 

 permit their behavior to produce its full effect. 



It may also be significant that plain-colored tanagers do sometimes 

 join and follow individuals of other species. Such reactions are rela- 

 tively very rare, but actually not too uncommon. Solitary individuals 

 and pairs of plain-colored tanagers may also approach individuals of 

 other species without performing clear-cut joining or following reac- 

 tions of the type recorded in the accompanying tables. This may be 

 the reason why the average number of plain-colored tanagers per 

 mixed flock is less than the average number per nonmixed flock (see 

 tables 2, 21, 29, and 36). It is perhaps unlikely that plain-colored 

 tanagers would approach, join, or follow individuals of other species 

 as frequently as they do if associations with other species were always 

 disadvantageous, especially as any approach to individuals of other 

 species will tend to induce these other individuals to join or follow 

 the plain-colored tanagers in return. 



PALM TANAGER 



The usual social role of palm tanagers in mixed blue and green 

 tanager and honey creeper flocks is at least as important as that of 

 plain-colored tanagers. In most circumstances, individual palm tana- 

 gers seem to become associated with mixed flocks approximately as 

 frequently as do individual plain-colored tanagers, when allowances 

 are made for the fact that the two species are seldom equally abundant 

 in any given area. Like the plain-colored tanagers, palm tanagers also 

 tend to stimulate the formation and increase the cohesion of mixed 

 flocks ; but the two species produce their effects in very different ways. 

 Palm tanagers are very active joiners and followers. In most circum- 

 stances they join and follow other species relatively much more fre- 

 quently than do any other tanagers of the blue and green tanager and 

 honeycreeper alliance. 



