Distribution and Abundance of Diurnal Mammals, Especially Monkeys, at Kasoje, Mahale Mountains, Tanzania

Abstract

Censusing was done by direct observation along three survey routes to estimate the distribution and abundance of medium- and large-sized diurnal mammals in the Kasoje area of the Mahale Mountains National Park, western Tanzania between 1995 and 1996. The census area is located within the home range of M Group chimpanzees who have been observed to consume at least 14 species of sympatric mammals. The vegetation along the three census routes was divided into two types of habitat (forest vs. woodland); as a result, six census subunits were distinguished. Preference of habitat by eight species of mammals -red-tailed monkey, blue monkey, yellow baboon, red colobus monkey, bushbuck, blue duiker, warthog, and forest squirrels - has been suggested and their group and/or individual densities have been estimated in at least one census subunit. In 1974, most villagers moved out of the Kasoje area following a government edict and the wild animal population in general appears to have increased in number since then. However, expansion or contraction in distribution of three species of mammals at Kasoje since the 1970s differs from species to species: yellow baboons and warthogs have apparently expanded their ranges while vervet monkeys seem to have contracted theirs. The abundance of red colobus monkeys appears to correspond with the high frequency of colobus hunting by the chimpanzees. However, it should be explained in the future why the second most abundant red-tailed monkeys, another resident arboreal species, have been eaten only infrequently by them. Further accumulation of observations on actual encounters between the chimpanzees and their potential prey is necessary.