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

Abstract 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.