l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



clearing when they were not in the trees, and it was felt that to count 

 only the variable seedeaters in trees would provide a very inadequate 

 sample of the population of the area and convey a misleading impres- 

 sion of the behavior of the species.) 



The method used in compiling table I (which was used in order 

 to obtain the largest possible count of associations between species) 

 has certain inevitable defects. It is probable, for instance, that some 

 birds that were really associated with mixed flocks were not counted 

 as members of such flocks simply because they did not happen to be 

 in the same trees as the other members of their flocks when they were 

 counted. It is also probable that some of the groups of birds that 

 were classified as mixed flocks during this count were essentially 

 chance aggregations of individuals that were not really reacting to 

 one another in any significant way. Many or most of the birds in 

 most of the groups, however, did show some tendencies to keep 

 together, at least intermittently or for brief periods of time. Many 

 of the groups seemed to be very well organized, composed of indi- 

 viduals that tended to join or follow one another in a very regular 

 manner. 



Perhaps the most conspicuous examples of groups held together 

 by relatively strong social bonds were flocks that moved about as 

 units, all the individuals of the group flying close together at the 

 same time and in the same direction. The number of times individuals 

 of different species were seen flying in such groups is also indicated 

 in table I under the heading "Number of times individuals seen in 

 obviously integrated mixed flocks." 



The figures in parentheses in table I are percentages of the total 

 number of times individuals of any given species were seen, both in 

 mixed flocks and not in mixed flocks. Thus, for instance, the 106 

 times individual plain-colored tanagers were seen in tightly integrated 

 mixed flocks are approximately 10 percent of the total number of 

 times (1,047) individual plain-colored tanagers were seen, both in 

 mixed flocks and not in mixed flocks. 



Table 2 may be considered a supplement to table 1. It is a record of 

 the same observations as those recorded in table I, summarized in a 

 different way. 



The number of times the different species (not the individual birds) 

 were seen in mixed flocks and not in mixed flocks is indicated in the 

 first two columns of table 2. In order to get these figures, individual 

 birds were not counted separately unless they were seen without any 

 other individuals of the same species nearby. Thus, for instance, when 



