As of the IUCN and other existing reports, most of the Colobine monkeys are not yet globally endangered. Nevertheless, many species are locally threatened. Therefore, data on Colobine population abundance and ecological preferences are important prerequisites for successful local and global conservation efforts but these data are often lacking. To address this gap, we estimated the abundance of Colobus guereza ssp. guereza in the moist evergreen-riverine forest part of Nech Sar National Park, Ethiopia. The survey was conducted using distance sampling. Based on a preliminary study, 17 newly cut line transects were randomly oriented over the study region to fully capture the distribution of C. g. guereza. Abundance estimation was analysed using ‘DISTANCE’ Program. Each census walk was completed every two weeks for three consecutive months, yielding a total of 195 detections over covering a total survey effort of 113.4 km. The mean group and mean animal density were 14 animals km-2 and 102 animals km-2, respectively. This resulted in a mean estimated abundance of 2,153 animals, distributed over the study region. The mean estimated group size was 7.24 with an estimated encounter rate of 1.72 n/L. In comparison with similar studies from the tropical forests of Africa, our population density estimates were among those intermediate values (100 to 168 animals per km2). We conclude that such intermediate density estimates, within the moist natural forests, reflect the fact that C. g. guereza had suffered from a human-induced reductions in habitat availability. However, repeating this survey would result a more comprehensive distribution-abundance (density) estimates. Furthermore, we recommend studies that address the foraging ecology, activity-time budgets, and population demography of these monkeys. Nonetheless, our results provide a reference point for future investigations in the area, particularly to assess population trends of C. g. guereza.
Keywords: Abundance, C. g. guereza, distance sampling, line transect, Nech Sar National Park
