98 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



throated redstarts probably also tend to enhance the conspicuousness 

 of mixed flocks, without contributing very much, directly, to enhance 

 the cohesion of the flocks. 



COLLARED REDSTART 



Collared redstarts are most common above 6,000 feet on the west- 

 ern slopes of the Volcan de Chiriqui ; but their behavior apart from 

 mixed flocks is very similar to that of slate-throated redstarts. It is 

 interesting, therefore, that their usual social role in mixed flocks is 

 much more important than that of slate-throated redstarts. 



Collared redstarts tend to join individuals of other species rela- 

 tively much more frequently than do slate-throated redstarts. Their 

 usual method of joining is very distinctive. They seldom fly directly 

 to join other birds, but make short flights to catch insects, and then 

 tend to land beside individuals of other species when they return 

 from their insect-catching flights. Slate-throated redstarts also make 

 short flights to catch insects ; but they do not show nearly as strong 

 a tendency to land beside individuals of other species on their re- 

 turn. This peculiar type of interspecific joining behavior would be 

 explained if collared redstarts were much more strongly attracted to 

 individuals of other species when they themselves are flying than 

 when they are not. 



Collared redstarts may land beside individuals of almost any other 

 species, but they seem to prefer sooty-capped bush-tanagers. Such 

 reactions may be expressions of a definite special interspecific prefer- 

 ence. (Collared redstarts are rare in areas where brown-capped bush- 

 tanagers are common. It is possible that they are as strongly at- 

 tracted to brown-capped bush-tanagers, when they meet them, as they 

 are to sooty-capped bush-tanagers ; but I did not see enough encoun- 

 ters between collared redstarts and brown-capped bush-tanagers to 

 be able to analyze the relations between the two species.) 



There are indications that the relative frequency of interspecific 

 joining reactions (compared with interspecific following reactions) 

 by collared redstarts is approximately the same as the corresponding 

 frequency of similar reactions by red- faced spinetails, and much 

 greater than the corresponding frequency of similar reactions by 

 yellow-thighed finches or Wilson's warblers. Collared redstarts may 

 follow individuals of other species slightly more frequently than do 

 slate-throated redstarts; but they certainly follow individuals of other 

 species much less frequently than they join individuals of other 

 species. They are also followed by individuals of other species rela- 



