92 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



In this area the members of a pair or family group of sooty- 

 capped bush-tanagers will sometimes try to follow a mixed flock, with 

 which they have been associating while the flock was in their ter- 

 ritory, when the flock leaves their territory. Such attempts are sel- 

 dom or never successful. As soon as the members of a pair or family 

 group of sooty-capped bush-tanagers overstep the boundary of their 

 territory, they find themselves within the territory of another pair or 

 family group of sooty-capped bush-tanagers. The owners of this latter 

 territory always, or almost always, rush to defend their territory, and 

 always, or almost always, manage to repel the intruders after a 

 more or less prolonged dispute. Such disputes are usually accom- 

 panied by a great variety of hostile patterns by both the intruders and 

 the defenders, including overt attack and escape movements and many 

 hostile calls and notes. Similar incidents are common among the yel- 

 low-thighed finches in the same area. Yellow-thighed finches also try 

 to follow mixed flocks into the territories of neighbors of their own 

 species, and provoke similar disputes as a result. 



The overt attack and escape movements performed during such 

 disputes among sooty-capped bush-tanagers and yellow-thighed 

 finches tend to have a disruptive effect upon any mixed flock in which, 

 or in the immediate vicinity of which, they occur. The other mem- 

 bers of the flock tend to scatter to get out of the way of the disput- 

 ing birds, which usually fly back and forth in a very energetic man- 

 ner. At the same time the hostile calls and notes of the disputing 

 birds are so attractive to birds of other species that the other mem- 

 bers of the flock do not usually scatter very far, and other birds that 

 were not associated with the flock before the dispute began may come 

 to join it. As a general rule it may be said that most of the mixed 

 montane bush flocks of this area are never more attractive than when 

 disputes among sooty-capped bush-tanagers and/or yellow-thighed 

 finches are going on inside them. Thus they are most attractive just 

 at the time when they are in greatest danger of disruption. This may 

 tend to prolong the existence of many of these mixed flocks. 



Such actions and reactions are particularly important in the 

 flocks slightly below 7,000 feet because the territories of sooty- 

 capped bush-tanagers and yellow-thighed finches tend to coincide in 

 this area. The territories of both species are partly determined by 

 the same aspects of terrain and vegetation, and boundaries are usu- 

 ally established where there are gaps in the shrubbery. Both species 

 tend to react to these gaps in the same way. Every patch of shrub- 

 bery in this area that is the territory of a single pair or family group 



