I wish to thank the Peruvian Ministry of Agriculture for permission to carry out the field study (authorization No. 56-85-DGFF-DRFF-SDFF). I am indebted to Drs. Jaime Moro S., Filomeno Encarnación C., and Luis Moya 1. from the Proyecto Peruano de Primatologia for their friendly help and support. I am grateful to Ursula Bartecki for companionship and essential help in the field and for critically reading earlier drafts of the manuscript. The paper benefited from critical comments of two anonymous referees. The study was financed through a grant from the Deutsche Forschungsgemeinschaft (Ku 131/8-1).
This is the extended version of a paper presented at the 12th Congress of the International Primatological Society in Brasilia.
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