Sudden short-term increase in mortality of vervet monkeys (Cercopithecus aethiops) due to leopard predation in Amboseli National Park, Kenya.

A substantial increase in mortality, due mainly to predation, occurred during 1987 in a population of vervet monkeys (Cercopithecus aethiops) studied from 1977 to 1989 in Amboseli National Park, Kenya. It has been shown that vervets moving into new and unfamiliar habitats are more at risk from predation. However, this does not entirely explain the increase in predation in 1987 because predation decreased after 1987 while movement into new areas continued. An increase in leopard alarm calls relative to previous years in four of five groups, and an association between disappearances and leopard alarm calls given by vervets in the same four groups, suggest that leopards, a main predator of vervets, accounted for the increase in mortality. The vervets' increased vulnerability to leopard predation in 1987 did not appear to be related either directly or indirectly to continued habitat deterioration because 1) mortality rates after 1987 decreased to pre-1987 levels and 2) the vervets' behavior did not appear to change to make them more vulnerable than in previous years. The increased vulnerability appeared to be due in part to an increase in the presence of leopards. However, it is unclear why predator presence temporarily increased.