Behavioral Ecology of Perceived Risk of Predation in Sympatric Patas (Erythrocebus patas) and Vervet (Cercopithecus aethiops) Monkeys in Laikipia, Kenya

In this dissertation, I explored how habitat structure affected perceived risk of predation and anti-predator behavior in closely related, sympatric patas (Erythrocebus patas) and vervet (Cercopithecus aethiops) monkeys in Laikipia, Kenya. While patas were restricted to non-riverine habitat at my study site, vervets used both non-riverine and riverine habitats. The use of two structurally different habitats by the vervets allowed me to examine the effect of differences in tree height and canopy cover across and within species while controlling for effects of group size, group composition, and phytogeny. During alarm calls at mammalian predators, vervets adjusted their antipredator behavior and acted more like patas when they were in areas with shorter trees. Tree height also affected perceived risk of predation in patas monkeys. Within the patas home range two distinct microhabitats with the same tree species differed in tree height. Patas preferred the tall microhabitat when grass height was similar. Within the preferred microhabitat, patas scanned more and fed less in tall trees. My results indicate that the increased visibility provided by tall trees may have increased the patas’ ability to detect predators. Visibility afforded by changes in ground cover can also affect animals’ perceived risk of predation. I examined the effects o f ground cover on the vervets’ behavior after a wildfire swept through an area near my study group’s home range. Reduced grass height after the fire enabled the vervets to see significantly farther. Vervets abruptly changed their ranging behavior and moved into the area that had been burned. They had not been observed in that area previously. The vervets scanned bipedally less often in the burned area, apparently because they perceived a reduced risk of predation due to increased visibility and reduced predator presence. My findings indicate that patas and vervet monkeys are sensitive to the structure of their immediate environments and change their behaviors to accommodate differences in habitat structure and predation risk. Habitat structure, therefore, is an important variable to consider when studying the variation in primate behavior.