2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



are usually found in groups, family parties of four or five individuals 

 and larger flocks of up to ten or twelve individuals. These flocks are 

 very active and mobile but tend to be long-sustained and well- 

 integrated, the members staying close together or coming together 

 repeatedly. Mobile flocks are smaller and less long-sustained on the 

 average during the breeding season, but individuals still follow one 

 another and feed together with some appreciable actual frequency. 

 They also show a definite tendency to form breeding "colonies." 

 Males defend individual territories during the breeding season, but 

 their territories often are small and crowded together in clusters. 

 Even when territories are large, the favorite perches or "stations" of 

 neighboring males may be only a few feet apart. No attempt was 

 made to discover or count nests during the present study, but it was 

 obvious, from the general density of populations, that nests could 

 not be very far apart in many areas (possibly they were less than 

 50 yards apart in some cases). It is also conceivable that some males 

 are sometimes polygynous. At least several adult males were seen 

 associating with two or more individuals in adult female or juvenal 

 plumage during the first part of the breeding season. 1 



The general social behavior of yellow-rumped tanagers in Panama 

 probably is quite similar to that of the scarlet-rumped or "song" 

 tanagers (R. passerinii) of Costa Rica described by Skutch, 1954. 2 



The preflight intention movements of yellow-rumped tanagers, 

 including ritualized Wing-flicking and Tail-flicking, and all their 

 observed unritualized hostile reactions, including both overt attack 

 and escape, seem to be nearly or completely identical in form with 

 the homologous patterns of crimson-backed tanagers (and, probably, 

 all other species of Ramphocelus) . Yellow-rumped tanagers also per- 

 form Gaping, which may be silent or accompanied by Hoarse Notes 

 (see below) and is usually superimposed upon or combined with 

 unritualized aggressive or advance ("pre-attack") movements or 

 intention movements. 



As would be expected, in view of their high degree of gregarious- 

 ness, yellow-rumped tanagers are noisy. Their vocal repertory 



1 Adult females cannot be distinguished from juvenile birds of both sexes in 

 the field by appearance alone. The individuals referred to as females, without 

 qualification, in the following account were those which performed obviously 

 sexual patterns with adult males. 



2 Yellow-rumped tanagers sometimes occur in mixed flocks with crimson- 

 backed tanagers. This may help to explain certain features of the display 

 behavior of the two species (see page 31). 



