Comparative Aspects of Social Organization in the Tana River Red Colobus, Colobus badius rufomitratus


Department of Biology, Universiti Kebangsaan Malaysia, Jalan Pantai Baru, Kuala Lumpur, Malaysia.


Red colobus living in gallery forests along the Tana River, Kenya, are usually found in groups of 12–30 animals, containing one, or at most two, adult ♂♂. These groups are much smaller than those at some rain forest sites and have a more disparate ratio of ♂♂ to ♀♀. A single study group censused regularly over 28 months varied in size from 16 to 33 animals. There were two replacements of adult ♂♂ and at least 34 migrations to or from the group by adult or subadult ♀♀. The incidence of extra-group animals in the study area is described. Although ♂♂ were quite commonly found outside reproductive groups, there appeared to be at least 6 times more adult ♀♀ in the population than adult ♂♂. It is hypothesized that the sex ratio within reproductive groups is influenced by the mortality rate amongst ♀♀ that leave those groups.