80 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



Chlorospingus nor Tangara seems to be particularly primitive among 

 tanagers. 14 



It seems likely, therefore, that much of the attractiveness of brown- 

 capped bush-tanagers to individuals of other species is due to their 

 possession of special characters that were originally evolved to pro- 

 mote intraspecific gregariousness. Individuals of other species are 

 probably usually or frequently attracted to them by the same charac- 

 ters that attract brown-capped bush-tanagers to one another; but 

 there are certain obvious exceptions to this general rule. 



Brown-capped bush-tanagers frequently dispute among themselves, 

 even during the nonbreeding season when they associate with one 

 another in relatively large groups. During such disputes they usually 

 utter many hostile vocalizations. All or most of these vocalizations 

 seem to function as a threat during intraspecific encounters. When 

 uttered by one brown-capped bush-tanager they usually induce other 

 brown-capped bush-tanagers to retreat, at least temporarily. 



There is some evidence that brown-capped bush-tanagers tend to 

 utter relatively more vocal threat patterns and perform relatively 

 fewer overt attack movements during intraspecific disputes than do 

 many related species in similar circumstances. This may be an adapta- 

 tion to promote intraspecific gregariousness, as vocal threats are prob- 

 ably less disruptive within a flock than overt attack movements. 



Interestingly enough, the vocal threat patterns of brown-capped 

 bush-tanagers may have an effect upon individuals of other species, 

 which is just the reverse of their usual effect upon other brown-capped 

 bush-tanagers. The sound of all or most of their threat calls seems 

 to be definitely attractive to individuals of some other species. This 

 may be illustrated by the behavior of some birds observed at approxi- 

 mately 5,700 feet elevation on the Volcan de Chiriqui between Octo- 

 ber 3 and October 10, i960. There were two or three pairs of family 

 groups of brown-capped bush-tanagers in this particular area at this 

 time. They roosted separately at night and began to move around and 

 feed separately at dawn. They were usually rather quiet when they 

 first began to move around and feed, and were not usually accom- 

 panied by individuals of other species. Sooner or later, in the course 

 of their wanderings, two of the pairs or family groups would come 

 face to face, apparently by accident. Such encounters would induce 

 an outburst of threat calls by some or all of the brown-capped bush- 



14 The phylogenetic relationships between different genera of tanagers and 

 finches will be discussed in a series of separate papers (in preparation) after 

 more detailed descriptions of their most significant behavior patterns. 



