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(Incidentally, earlier this morning, in general region where I saw mixed flocks with yellow-faced Whitestarts,I [[underlined]] thought [[/underlined]] I heard occasional Slate-throat songs as well. If no, the songs of the 2 species of Whitestarts probably did not overlap.) A few seconds later, see same pair Slate-throats [[underlined]] associating [[/underlined]] with 2 or more BCBT's (identification definite) in adjacent trees. All birds 10-20 ft up. BCBT(s) utter(s) occasional R's. Then group moves off. Can't see who is leading who. Are Slate-throats Allogregarious here, as in Western Cordillera? Leaving 9:15 am COMMENT: Looking over my 1962 notes, I realize that the resemblance between the mixed flocks here now and the flocks observed in the same place earlier is even greater than I thought. Some of the flocks seen in 1962 also were diffuse. And at least one of the 1962 flocks also included Slate-throats This is [[underlined]] very good [[/underlined]] evidence that social behavior tends to be stable over periods of at least several years. ([[Viz]] also observations in the Eastern Cordillera) In general, the social behavior of the birds here resembles that of the birds on Purace-- [[underlined]] except [[/underlined]] that the flocks here are more diffuse In this connection, it is well to remember that the number of species seems to be much smaller here than in Purace! This suggests two conclusions: (1) The [[underlined]] frequency [[/underlined]] with which mixed flocks are formed [[underlined]] is independent of the number of species present in an area. [[/underlined]] (2) The [[underlined]] cohesiveness [[/underlined]] of mixed flocks, on the other hand, [[underlined]] is positively correlated with the number of species present and/or dependent upon the presence of partic [[/underlined]]