Relative abundance and distribution of black-and-white colobus monkey (Colobus guereza guereza) in northwestern Ethiopia

Forest loss, fragmentation, and degradation are major threats to primates. In areas that have been heavily deforested, it is critical to identify the distribution and abundance of remaining primate populations to inform conservation actions. The Ethiopian Highlands have lost most of its original forest cover and the remains are highly fragmented. The black-and-white colobus monkeys (Colobus guereza guereza) are a subspecies of the Colobus guereza endemic to Ethiopia. Their restricted distribution in fragmented forest habitats along with further habitat loss renders them vulnerable to local extirpation. To date, the population size and distribution of black-and-white colobus monkeys are unknown along the Ethiopian Highlands. Therefore, we aimed to determine the relative abundance of black-and-white colobus monkeys and their distribution pattern in northwestern Ethiopia. We conducted population surveys using line transects between Oct 2020 and Sep 2021 in 27 forest patches that ranged between 1859 and 2557 m asl in elevation (mean = 2164.9, SD = 178.6). We recorded 328 groups of black-and-white colobus monkeys, and they were observed in all 27 forest patches. We counted a total of 2897 individuals ranging from 5 to 16 individuals per group (mean = 8.8, SD = 2.5) within the sampling transects. Overall, the sighting encounter frequency of this monkey was 5.5 groups/km, while the relative mean population abundance was 48.2 individuals/km. Our study offers the first baseline information for future absolute abundance and population density estimates of black-and-white colobus monkeys and the forest patches they inhabit in northwestern Ethiopia. The establishment of protected areas, improved law enforcement, population monitoring, and engagement with adjacent local communities are imperative to secure the long-term survival and conservation of black-and-white colobus monkeys and their habitats in the region. In addition, conservation measures like educational awareness programs, modern beekeeping, and alternative biofuel use should be initiated to stop further deforestation.