The impact and implications of vehicle collisions on the endangered and endemic Zanzibar red colobus (Piliocolobus kirkii)

Roads can affect wildlife in a variety of negative ways. Studies of road ecology have mostly concentrated in the northern hemisphere despite the potentially greater impact on biodiversity that roads may have in tropical habitats. Here, we examine a 4-year opportunistic dataset (January 2016 – December 2019) on mammalian roadkill observed along a road intersecting Jozani-Chwaka Bay National Park, Unguja, Zanzibar. In particular, we assess the impact of collisions on the population of an endangered and endemic primate, the Zanzibar red colobus (Piliocolobus kirkii). Primates accounted for the majority of roadkill. Monthly rainfall variation was not associated with roadkill frequency for mammals and specifically for the Zanzibar red colobus. No single age-sex class of colobus was found dead more often than expected given their availability in the local population. The exact effect of roadkill on colobus populations in habitats fragmented by roads is unknown given the lack of accurate, long-term life history data for this species. However, the frequency of kills documented in this study suggests further mitigation measures may be important. Our data show that mortality from collisions with vehicles in some groups of colobus are comparable to rates of mortality experienced by other primate populations from natural predation. Unlike natural predators, however, vehicles are not ‘selective’ in their targeting of ‘prey’. The long-term implications of such a ‘predation regime’ on this species remain to be established.