82 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



role of brown-capped bttsh-tanagers in mixed flocks is facilitated by 

 their tendency to range through many different levels of vegetation. 

 They are most often found moderately high (approximately 10 to 40 

 feet above the ground) in medium-sized trees and tall shrubbery; but 

 they also occur in the tops of very tall trees and in very low shrubbery 

 only a few inches above the ground. They probably occur at both 

 extreme levels of vegetation more often than individuals of most 

 other species of the montane bush alliances ; and they frequently move 

 from one extreme to the other or alternate between the two extremes 

 very rapidly. Thus they tend to encounter a wide diversity of individ- 

 uals of many different species, including species that are rather strictly 

 confined to comparatively narrow levels of vegetation. 



It is my impression that brown-capped bush-tanagers tend to play a 

 less important role in lower-altitude mixed montane bush flocks, be- 

 low approximately 5,200 feet, than in higher-altitude mixed mon- 

 tane bush flocks. They seem to be joined and followed by individuals 

 of other species relatively less frequently in the lower-altitude flocks 

 than in the higher-altitude flocks. Part or all of this difference seems 

 to be due to the fact that brown-capped bush-tanagers are usually rela- 

 tively less conspicuous in the lower-altitude flocks. They tend to be 

 relatively rare at lower altitudes. The lower-altitude flocks also tend 

 to include individuals of more species than the higher-altitude flocks ; 

 and some of the species that occur in lower-altitude flocks but not in 

 higher-altitude flocks are very noisy and/or very restless. Thus the 

 attention of the other members of the lower-altitude mixed flocks is 

 more often distracted, i.e., diverted from the brown-capped bush- 

 tanagers, than is that of the other members of the higher-altitude 

 mixed flocks. 



The brown-capped bush-tanager must be classified as a passive 

 nuclear species. Its social role in mixed flocks is not, however, quite 

 as one sided as that of the plain-colored tanager. It seems to join and 

 follow individuals of other species slightly more frequently than do 

 plain-colored tanagers. 



The range of the brown-capped bush-tanager on the Volcan de 

 Chiriqui overlaps that of the sooty-capped bush-tanager to some ex- 

 tent. Brown-capped bush-tanagers may react to sooty-capped bush- 

 tanagers more strongly than they do to individuals of many other 

 species. At least I have heard them begin to utter hostile calls when 

 they heard sooty-capped bush-tanagers utter hostile calls in the dis- 

 tance. But such reactions are relatively very rare and very brief. I 

 have never heard brown-capped bush-tanagers utter more than a few 



