NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 6j 



erences of the most commonly observed species of the blue and green 

 tanager and honeycreeper alliance. Diagram I shows the special inter- 

 specific preferences revealed by predominantly friendly joining and 

 following reactions. Diagram 2 shows the special interspecific prefer- 

 ences revealed by supplanting attacks and other predominantly aggres- 

 sive reactions. Both diagrams may be incomplete ; but they probably 

 include all or almost all of the strongest and most significant special 

 interspecific preferences of the regular members of typical mixed blue 

 and green tanager and honeycreeper flocks in central Panama. 



In spite of their distinctness, the roles of the various species occur- 

 ring in mixed blue and green tanager and honeycreeper flocks may be 

 classified into a small number of rather broad categories. Such a 

 classification may be useful for comparative purposes. 



There have been several previous attempts to classify the social 

 roles of species occurring in different types of mixed flocks in different 

 areas of the Tropics. 



In his first paper on mixed flocks of Rhodesian birds, Winterbottom 

 ( io 43)> divided the species of such flocks into two categories: 

 "nucleus" species and "circumference" species. Individuals of the 

 nucleus species always occurred in groups, by themselves alone, or in 

 association with individuals of other species. Individuals of the cir- 

 cumference species were not highly gregarious among themselves, but 

 did join mixed flocks. Winterbottom suggested that most mixed 

 flocks were formed by circumference species joining nucleus species. 

 The terms themselves would suggest that individuals of the nucleus 

 species usually occurred at the front and/or the center of mixed flocks 

 and the circumference species at the sides and/or toward the rear 

 of the flocks. 



Davis (1946) classified the species of mixed flocks in some Brazilian 

 forests according to several criteria. His main categories were "regu- 

 lar" species and "accidental" species. These were defined as follows : 

 "The regular species stay with the flock for long periods of time, are 

 seldom seen away from the flock, and have the calls and behavior 

 patterns of a flocking species. . . . The accidentals associate merely 

 temporarily with the group as it moves along. These species do not 

 have the calls and behavior of flocking birds." Davis also recognized 

 categories of "migrants," species that "are present for either the 

 breeding or the nonbreeding period," and "nomads," species that "are 

 irregular in occurrence and vary greatly in numbers." 



In a later paper, Winterbottom (1949) attempted to combine 

 Davis's classification with his own earlier classification, and suggested 



