112 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



between December 17 and December 24, 1958, near Iquitos in the 

 Amazonian region of eastern Peru. 



CRIMSON-BACKED TANAGERS AND YELLOW-RUM PED TANAGERS 



Adult male yellow-rumped tanagers are largely pure velvety black, 

 with whitish bills and bright lemon yellow on the lower back and 

 rump. Adult females and young of both sexes are generally brown- 

 ish, with yellow lower back, rump, breast, and belly. 



Yellow-rumped tanagers show a much higher degree of intra- 

 specific gregariousness than crimson-backed tanagers. They tend to 

 form flocks of 8 to 12 individuals (i.e., definitely larger than a single 

 family group of parents and one brood of young). Such flocks seem 

 to be maintained rather steadily throughout the nonbreeding season, 

 and also occur, at least occasionally, in the breeding season. 



Like most other highly gregarious birds, yellow-rumped tanagers 

 are very restless and noisy. Some of their more complex calls are 

 quite distinctive, very different from any calls of any other tanager 

 or related species occurring in the lowlands of central and eastern 

 Panama ; but their most common notes are very similar to those of 

 crimson-backed tanagers in sound. Both yellow-rumped tanagers and 

 crimson-backed tanagers utter thin tseeet notes and nasal anh notes 

 very frequently. 



The habitat preferences of yellow-rumped tanagers and crimson- 

 backed tanagers are similar in some ways and different in others. Both 

 species prefer scrub, but yellow-rumped tanagers prefer scrub along 

 the banks of rivers and streams, and crimson-backed tanagers prefer 

 scrub in slightly higher and drier areas some distance away from the 

 banks of rivers. Yellow-rumped tanagers sometimes stray away from 

 their usual habitats, and move into typical crimson-backed tanager 

 habitats; but such occurrences seem to be relatively rare. Crimson- 

 backed tanagers seem to occur in typical yellow-rumped tanager habi- 

 tats somewhat more frequently. 



All my observations of yellow-rumped tanagers and crimson-backed 

 tanagers in the same flocks were made in typical yellow-rumped tana- 

 ger habitats. In such habitats, yellow-rumped tanagers are always 

 much more abundant than crimson-backed tanagers. 



It is usually apparent in such habitats that crimson-backed tanagers 

 tend to stay closer to yellow-rumped tanagers than to any other tana- 

 gers, honeycreepers, or finches in the same area at the same time. They 

 may also follow and join yellow-rumped tanagers in a clear-cut and 

 conspicuous manner more frequently than they follow and join all 



