Primate community dynamics in old growth forest over 23.5 years at Ngogo, Kibale National Park, Uganda: Implications for conservation and census methods

Few data exist regarding long-term changes in primate populations in old-gr owth, tropical forests. In the absence of this information, it is unclear h ow to assess population trends efficiently and economically. We addressed t hese problems by conducting line-transect censuses 23.5 years apart at the Ngogo study area in Kibale National Park, Uganda. We conducted additional c ensuses over short time intervals to determine the degree to which the temp oral distribution of censuses affected estimates of primate numbers. Result s indicate that two species, blue monkeys and red colobus, may have experie nced significant reductions over the past 23.5 years at Ngogo. In contrast, five other species, baboons, black-and-white colobus, chimpanzees, mangabe ys, and red-tailed guenons, have not changed in relative abundance. Additio nal findings indicate that different observers may vary significantly in th eir estimates of sighting distances of animals during censuses, thus render ing the use of measures of absolute densities problematic. Moreover, census es conducted over short periods produce biased estimates of primate numbers . These results provide guidelines for the use of line-transect censuses an d underscore the importance of protecting large blocks of forests for prima te conservation.