Habituation and decline of anti-predator behaviours in colobus monkeys in dog-dense suburban Kenya

Domestic dogs (Canis familiaris) are an invasive species that can affect wildlife behaviour and contribute to species extinction. In Diani and Galu, southeastern Kenya, they injure or kill colobus monkeys (Colobus angolensis palliatus) more than the other monkey species in the area. This study investigated how arboreal colobus in these suburban areas adjust anti-predator strategies to a dog-dense environment. From May to July 2018, we conducted focal follows on two colobus groups (Group A: 103 h; Group B: 98.5 h) with home ranges overlapping with dogs and where previous dog-colobus attacks were witnessed. Dog-colobus interactions (⩽20 m from a dog) occurred in 2% of observation hours, with 70% of interactions involving dog predatory behaviours. The primary anti-predator behaviour was vigilance during the interactions and moving away rather than fleeing. When we mapped these interactions, the high-risk areas accounted for 12 and 13% of the total home ranges, respectively. Both groups spent about half their time foraging in these high-risk areas, did not stay high in the vegetation while there, and did not socialise or rest more frequently in the low-risk areas. A 1969 study of colobus vocalisations in the same area described colobus responding to dogs with vocalisations, threat displays, and fleeing - typical anti-predator behaviours of the genus. We conclude that over 55 years of exposure and habituation to dogs in a rapidly growing suburban environment have diminished anti-predator responses. Although frequently employed anti-predator behaviours would be energetically costly, reduced expression may ultimately increase colobus vulnerability to dog predation.