With thirteen species (Hershkovitz, 1990), Callicebus is one of the most diverse but poorly studied genera of neotropical primates. Long-term field studies have been conducted on only two of the 13 recognized Callicebus species. (1985) investigated dusky titis, C. brunneus (taxon replaces C. moloch) for 63 complete days during 11 months at the Cocha Cashu Biological Research Station in the Manu National Park of Peru. Callicebus torquatus, the yellow-handed titi has been the subject of a number of both short- and long-term studies by Freese (1975), Kinzey (1975, 1977, 1981), Kinzey ’ Gentry (1979), Izawa (1976) and (1982). A short-term study which consisted of six complete days during October and November 1977 were made on the ecology of masked titis, Callicebus personatus (Kinzey ’ Becker, 1983).