NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 99 



tively much more frequently than are slate-throated redstarts. It is 

 difficult to see exactly why this should be so, as they are not very 

 much more conspicuous or active than slate-throated redstarts. Per- 

 haps collared redstarts are followed more frequently because they fly 

 away from the close proximity of individuals of other species more 

 frequently. (They are close to individuals of other species more fre- 

 quently simply because they join individuals of other species more 

 frequently.) All other factors being equal, the sight of a bird taking 

 flight a few inches away is much more likely to induce another bird to 

 follow than the sight of a bird taking flight a few feet or yards away. 



Like slate-throated redstarts, collared redstarts are followed by 

 Wilson's warblers much more frequently than by individuals of any 

 other species; but they are also followed, not infrequently, by such 

 birds as yellow-thighed finches and sooty-capped bush-tanagers, birds 

 that seldom or never follow slate-throated redstarts. Collared red- 

 starts may be followed by individuals of other species relatively as 

 frequently as are sooty-capped bush-tanagers. 



Collared redstarts sometimes appear to be the leaders of mixed 

 flocks. Sometimes a whole mixed flock will move in the direction in 

 which a collared redstart is making most of its insect-catching flights. 

 This sort of movement is undoubtedly significant, at least in some 

 cases ; but the appearance of leadership by collared redstarts is prob- 

 ably often slightly deceptive. In many large flocks composed of many 

 species, collared redstarts may lead some but not all the other mem- 

 bers of the flocks. One or two collared redstarts, for instance, may 

 be followed by one or two yellow-thighed finches and/or sooty- 

 capped bush-tanagers, which are followed, in turn, by individuals of 

 other species. In such cases, the individuals of other species do not 

 usually continue to move after the collared redstarts if the yellow- 

 thighed finches and/or the sooty-capped bush-tanagers go in a differ- 

 ent direction. 



(There is at least one area on the Volcan de Chiriqui, near 6,000 

 feet, where the birds of the local montane bush alliance are often di- 

 vided into two types of flocks that are rather comparable to the "pre- 

 dominantly tanager" and "predominantly honeycreeper" flocks of the 

 blue and green tanager and honeycreeper alliance. In this area there is 

 a great deal of low scrub plus a few scattered very tall trees. The 

 foliage of the tall trees is usually separated from the underlying scrub 

 by a wide open space. 



Most of the members of the montane bush alliance in this area 

 tend to stay in the low shrubbery ; but a few species spend consider- 



