Population size and habitat preference of the Vulnerable Bale monkey Chlorocebus djamdjamensis in Odobullu Forest and its distribution across the Bale Mountains, Ethiopia

The Bale monkey Chlorocebus djamdjamensis is a little-known primate endemic to the south-eastern highlands of Ethiopia. From August 2007 to May 2008 we surveyed to determine the species' habitat preferences and population size in the Odobullu Forest and its range across the Bale Mountains. In Odobullu Forest a total of 136 transects of 1.8-3.0 km were surveyed over a total distance of 280 km. Bale monkey groups were encountered only in bamboo forest, suggesting that the species is a bamboo forest specialist. The density and population size of the Bale monkey in the bamboo forest of Odobullu Forest were estimated to be 121-141 km(-2) and 1,718-2,002, respectively. At a larger scale, we assessed the distribution of the Bale monkey in 40% of the bamboo forest across the Bale Mountains within the species' altitudinal range of 2,400-3,250 m. We identified the areas to be surveyed using a 200 m digital elevation model and a 10-m resolution satellite image. We found the Bale monkey in five areas, three of which are previously unrecorded locations for the species. The Bale monkey is now categorized as Vulnerable on the IUCN Red List, partly based on the results of our surveys. Although extensive, our surveys did not cover all of the species' potential habitat and further surveys are required across all of the bamboo forest of the Bale Mountains and Sidamo region (the western extension of the Bale Mountains).