A Further Decline in Numbers of Amboseli Vervet Monkeys

Abstract

A recensus of the Amboseli vervets in 1975 -revealed a significant decline of about 43 percent in their numbers since 1964. The young juvenile age class showed the greatest decrease; the juvenile age class had declined less. Numbers of adults and subadults seemed unaffected, although there was a suggestion of an incipient decline in the males of these two age classes. This decrease in vervets is attributed to a natural reduction in their food resources. Natality remained high, and the birth season had not changed. IN AN EARLIER PAPER I noted the reduction in numbers of vervet monkeys (Cercopithecus aethiops) living in the Amboseli Game Reserve, Kenya, which occurred between two study periods, 1963-1964 and 1971 (Struhsaker 1973). This decline in vervet numbers was attributed to a natural reduction in their food resources (see Western and Van Praet 1973 for details of this change of habitat). Since 1971 the food plants of Amboseli vervets, particularly the fever trees (Acacia xathophloea), have continued to die off. In an attempt to monitor this dynamic situation further, another recensus of six of the main study groups of vervets was made between 9 and 13 February 1975. These counts clearly show a further decline in their numbers and group size.