Abundance and Foraging Ecology of the Black and White Colobus Monkey (Colobus guereza ssp. guereza) in Nech Sar National Park, Ethiopia

Abstract

We estimated the abundance of Colobus guereza ssp. guereza in the moist evergreen riparian forest part of Nech Sar National Park, Ethiopia. The survey was conducted using the distance sampling method. Based on a preliminary study, 17 newly cut line transects were randomly aligned across the study area. The survey data were then collected for three consecutive months. Transects were walked once per month for 14-16 days. Abundance estimates were analyzed using the program 'DISTANCE'. The half-normal key function with cosine adjustment fitted our data sets best. Mean group density and mean animal density were 14 animals km-2 and 102 animals km-2, respectively, resulting in a mean estimated abundance of 2,153 animals distributed over thestudy area. The mean estimated group size was 7.24 with an estimated encounter rate of 1.72. Compared to similar studies from tropical forests in Africa, our population density estimates were intermediate between the mean values (100 to 168 animals km-2). We conclude that such intermediate density estimates reflect the fact that guerezas have suffered from human-induced reductions in habitat availability. We also suggest that the natural forest is still in a reasonable condition that likely provides them with sufficient food supply to compensate for such intermediate densities. However, a replication of this study would lead to a more comprehensive abundance estimate. We also recommend studies that would address the activity-time budget and populationdemographics of these monkeys. Nonetheless, our results provide a reference point for future studies in this area, particularly to assess population trends of C. g. guereza.