Diurnal primate densities and biomass in the Kakamega Forest: An evaluation of census methods and a comparison with other forests

Line-transect surveys were conducted at the Isecheno study site in the Kaka mega Forest, western Kenya to estimate diurnal primate densities. The estim ates from several different methods of analysis of census data were compare d to "true" density values based on home range size and overlap for two spe cies. The Whitesides method [Whitesides et al., 1988], which incorporates s pecies-specific mean group spread into its formula for estimating transect width, provided the most accurate density estimates. The importance of incl uding as many groups as possible when calculating density from home range s ize and overlap is demonstrated with long-term data from Colobus guereza an d Cercopithecus mitis. Colobus guereza group density at Isecheno was much l ower than that published from a recent brief study [von Hippel, 1996]. Cerc opithecus mitis group density has fallen while overall population biomass a ppears to have remained stable over 20 years of study. Isecheno has the sec ond highest diurnal primate biomass of the ten Guineo-Congolian rainforest sites for which biomass data are available, despite having the lowest prima te species richness. Within the Guineo-Congolian rainforest system, primate biomass appears to vary to some extent between ecogeographic regions: two of three mid-elevation East African sites have high biomasses, two of two l owland West African sites have intermediate biomasses, and four of five low land Central African sites have low biomasses. There is a strong positive c orrelation between total colobine biomass and total primate biomass at the ten Guineo-Congolian rainforest sites. (C) 2000 Wiley-Liss, Inc.