96 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 143 



It would thus appear that Wilson's warblers are almost completely 

 undiscriminating in their choice of associates — less discriminating than 

 any other species frequently associated with mixed montane bush 

 flocks, with the possible exception of summer tanagers (see below). 

 They seem to be equally satisfied to become associated with almost 

 any other montane passerine birds. This lack of discrimination is 

 really quite remarkable. 



It is relatively very rare to see two or more Wilson's warblers close 

 together, or associated with the same mixed flock at the same time, 

 because they usually fight among themselves whenever they come 

 within 10 or 15 yards of one another. They seem to be very strongly 

 territorial in Panama. The fights between Wilson's warblers are al- 

 most always brief and decisive. One bird attacks and the other usually 

 flees immediately. Such fights are seldom accompanied by any un- 

 usually loud burst of calling or other displays such as are common 

 during disputes among bush-tanagers or yellow-thighed finches. The 

 inconspicuous nature of such fights may be advantageous, in the case 

 of Wilson's warblers, because it may help to prevent others of this 

 species from being attracted to, and attempting to join in, the fights 

 when the disputing birds might be unable to repel additional intruders 

 very promptly. (Disputes among individuals of many other species 

 of birds are sometimes attractive to other individuals of the same 

 species as well as other species.) Anything that helps to prevent or 

 reduce intraspecific gregariousness is presumably advantageous in the 

 case of Wilson's warblers in Panama. 



Wilson's warblers are quite conspicuous in other ways, however. 

 They are brightly colored, and utter very loud call notes almost con- 

 stantly (if not usually very rapidly). As neither their colors nor their 

 notes are very different from those of many other species of the mon- 

 tane bush alliances, it is perhaps surprising that they are not joined 

 and/or followed more frequently by individuals of other species. Their 

 comparatively slight attractiveness may be due to their very slight 

 degree of gregariousness among themselves in Panama. As noted 

 above, single birds are probably always less attractive than pairs or 

 larger groups of the same species, all other factors being equal. 



Wilson's warblers certainly tend to enhance the conspicuousness 

 of the mixed flocks with which they are associated and probably, 

 therefore, increase the attractiveness of such flocks to other birds ; but 

 they seem to contribute relatively little, directly, to increase the co- 

 hesion of the flocks. 



