Vehicle Collisions Among Four Species of Monkeys Between 2000 and 2018 on a Suburban Road in Diani, Kenya

The impacts of road infrastructure on wildlife are of mounting concern. Amidst a growing body of literature on vehicle–wildlife collisions, few studies focus on primates. We examined a long-term dataset (2000–2018) of community-reported welfare cases for four species of monkeys: colobus ( Colobus angolensis palliatus ), Sykes’s monkey ( Cercopithecus mitis albogularis ), vervet ( Chlorocebus pygerythrus hilgerti ), and baboon ( Papio cynocephalus cynocephalus ). We analyzed collision rates using annual census data along a 10-km road section through the suburban town of Diani, Kenya. Vehicle–monkey collisions represented 705 of 1896 cases (37%), which was the most common anthropogenic cause of injury and death. The mean number of monthly vehicle–monkey collisions was 3 (range 0–10), and 83% of collisions led to death of the monkey. We found 1) higher degrees of terrestrialism were associated with lower number of collision cases; 2) no differences in the collision rates between juveniles, subadults, and adults across species, but collisions involving infants occurred at lower rates; 3) similar collision rates for female and male colobus and baboons, whereas Sykes’s monkey females and vervet males were more frequently involved in collisions than the other sex; 4) no correlation between the number of hotel bed-nights (a measure of tourist numbers) and vehicle collisions; and 5) drier days correlated with increased rates of vehicle–monkey collisions across all species. This study highlights the risks of roads for monkeys, and that collision rates vary with species, age class, and, in some species, sex and that rainfall is one factor that affects these rates.