Population Density and Seasonal Distribution of Endangered Zanzibar Red Colobus Monkeys (Piliocolobus kirkii) along a Conservation Gradient in Jozani Chwaka Bay Biosphere Reserve

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Globally, non-human primates face increasing extinction risks due to habitat loss and fragmentation driven by anthropogenic pressures. The Zanzibar red colobus monkey (Piliocolobus kirkii ), an endangered and endemic species of Unguja Island, is particularly threatened by ongoing habitat degradation both within and outside protected areas. Although conservation efforts have largely focused on the Jozani Chwaka Bay National Park, the species also relies on adjacent human-dominated transitional zones, which remain under-represented in conservation planning. This study assesses the population density and seasonal distribution of P. kirkii across a conservation gradient within the Jozani Chwaka Bay Biosphere Reserve to provide evidence for more integrated conservation strategies. Utilizing distance sampling surveys, we count P. kirkii individuals and groups during the dry and wet seasons along 100 evenly spaced 1 km foot transects, situated across a conservation gradient ranging from strictly protected national park (source) to less strictly managed transition zones (sinks). We used QGIS to map the seasonal distribution of the species across the areas. We encountered a total of 125 groups (74 groups in the national park and 51 in the transitional zone) during the dry and wet season surveys. Densities were higher in the national park, with 46.4 individuals/km2 compared to 12.5 individuals/km2 in the transitional zone. Similarly, group densities were higher in the national park (2.5 clusters/km2) than in the transitional zone (0.96 clusters/km2). Population density varied seasonally, with higher densities (25.4 individuals/km2) in the national park during the wet season and lower (23.5 individuals/km2) in the dry season, whereas the transitional zone showed the opposite pattern, with higher densities (7.5 individuals/km2) in the dry season and lower (4.9 individuals/km2) in the wet season due to changes in food availability. In the wet season, monkeys appear widely distributed across both park and transitional zones, as much of the vegetation becomes greener in both areas, indicating the presence of enough food during this time. The shift in habitat use highlights the interdependence of both the park and the transitional zone for the species' survival. Our study highlights the need for integrated conservation strategies that include both zones rather than relying solely on the national park.