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[[circled]]53[[/circled]]
rth and south are similar, more or less, but the center is quite different.)
The fact that mixed flocks were so highly developed in the areas visited today would tend to support (3). But humidity cannot be the whole answer. Mixed flocks seem to be highly developed in the northern part of the Central Cordillera, which does not seem to be very humid. And they do not seem to be highly developed in the Palea region of central Peru or the Machu Pichu region of sourthern Peru, both of which do seem to be very humid.
No (4) must have some effect (viz Chiriqui?). But again it cannot be the whole answer. The Central Cordillera is [[underline]]not[[/underline]] isolated.
This leaves me with (5) and (6). No. (5) must have some validity (viz the frequency of mixed flocks in southern Andes). [[underline]]But  (6) must also be important.[[/underline]] As mentioned in my notes of flocks of the Western Cordillera (p. 13), this would seem to be the only way to explain why mixed flocks are approximately as highly developed in the Central Cordillera as in the Western.

May 22, 1965
Tijeras
Going to work in area where [[underline]] Agrionis - Pipreola - Tangara negro - virides [[/underline]] group seen yesterday. Arrive at 5:30 am. Just getting by at Cloudy Altitude, according to my instruments now, is 8500 ft, 2575 mi
Quite a lot of bird sound. Probably mostly thrush Song Then a greater variety of sounds 5:40 am. Nothing I recognize.
5:45 am. See single [[red checkmark]] Yellowbelly. Perched exposed 20 ft up on bare bra