Il6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



ceived by the appearance of dusky-tailed ant-tanagers, which are simi- 

 lar to crimson-backed tanagers in shape and many of their actions, 

 and the males of which are brownish with some red on the throat and 

 crown. The young crimson-backed tanagers may be reacting to dusky- 

 tailed ant-tanagers as they would to other members of their own 

 species.) 



SILVER-BILLED TANAGERS AND BLACK-THROATED TANAGERS 



The silver-billed tanagers and black-throated tanagers that were ob- 

 served associating with one another were relatively few in number, 

 one family group (parents with two or three young) of each species. 

 These two families roosted separately at night, but usually came to- 

 gether shortly after dawn and spent an appreciable part of every day 

 together for at least seven consecutive days (as long as my observa- 

 tions continued). These birds are very similar in shape and, to a 

 lesser extent, color (red and black). Individuals of both species utter 

 tseeet notes very frequently. 



The social roles of the two species in this mixed flock were not 

 very well differentiated. Sometimes the silver-billed tanagers joined 

 and followed the black -throated tanagers; and sometimes the black- 

 throated tanagers joined and followed the silver-billed tanagers. 

 Both types of reactions were quite common, in both directions. Pre- 

 sumably further observations would have shown that one species 

 joined and followed the other species at least slightly more frequently 

 than the reverse, on the average, over a long period of time; but my 

 observations were too brief to permit a quantitative analysis of the re- 

 actions between the two species. Interspecific supplanting attacks and 

 other hostile patterns were quite common in this mixed flock. Some- 

 times one species was the aggressor, and sometimes the other. 



Competition for food between the two species was certainly in- 

 creased when they associated with one another. When they were not 

 together the silver-billed tanagers usually stayed in moderately to very 

 low scrub, while the black-throated tanagers usually stayed at a some- 

 what higher level in low trees. When they were together, however, 

 the individuals of both species usually moved and fed at the same level, 

 apparently eating the same foods. This change was usually due to a 

 change in the behavior of the black-throated tanagers, which when 

 they were associated with the silver-billed tanagers, frequently came 

 down into scrub that was lower than anything they visited when they 

 were alone. 



