Impact, evaluation, and mitigation of linear infrastructure development on primates in Diani, Kenya

Roads and electrical infrastructure are essential for achieving the United Nations Sustainable Development Goals. Twenty-five million kilometres of new roads are expected to be built globally by 2050, and governments are targeting universal access to electricity. However, linear infrastructure is known to have devasting impacts on wildlife including a wide range of non-human primates. Yet, the effects and the complex interactions between these various impacts are often overlooked, particularly in urban environments. This thesis examines the effects of roads and power lines on six primate species in Diani, a town in southeastern Kenya where development is interspersed with forest patches of a Global Biodiversity Hotspot. The research draws on 25 years of data on primate populations and cases of injury and death, collected by Colobus Conservation, a local conservation organisation. The data show that colobus monkeys suffer significant losses, with approximately 8% of the population affected annually due to vehicle collisions and electrocutions. Sykes' monkeys, vervets, and baboons experience sustainable losses (3.3%, 2.0%, and 1.8%, respectively), but these still represent over 1,000 individuals reported injured or killed since the organisation's inception in 1997. The impact on two species of galagos remains uncertain. This study highlights key ecological factors that influence species' vulnerability to roads and power lines, with arboreal species at higher risk on roads than more terrestrial species and larger individuals of arboreal species are at higher risk on power lines. The efficacy of canopy bridges in mitigating the road barrier effect and primate-vehicle collisions was assessed and shown to be successful and cost-effective overall. In addition, this research highlights that a commonly used approach to quantify the number of wildlife-vehicle collisions and electrocutions-carcass surveys-underestimate the true scale, because injured individuals who survive the initial impact make up a significant proportion of total collisions. This thesis found that correction factors of 1.5 for vehicle collisions and 2.15 for electrocutions are needed to improve carcass survey estimates. Regarding power lines, Diani's growth has not led to an increase in electrocution cases, indicating that the mitigation strategies of trimming vegetation near power lines and insulating cables are effective. Overall, this thesis calls for the protection of wildlife to be explicitly considered in road and electricity infrastructure planning by using the findings of this and previous research.