Rehabilitation release of vervet monkeys (Chlorocebus pygerythrus hilgerti) in south coast Kenya: A Scientific Approach

Abstract

Translocation is a tool for conserving animals and their environment. It is a complex process that involves detailed planning and preparation. The IUCN/SSC/RSG specifies the need for scientific employment in all animal translocation programmes pre-, during- and post-release. In this thesis, I aimed to follow and employ guidelines as detailed by IUCN/SSC Reintroduction Specialist Group for a rehabilitation release of vervet monkeys (Chlorocebus pygerythrus hilgerti) in Kenya. Additionally, I aimed to provide measures of post-release success, using verifiable indicators and criteria against which the release could be quantified. This was achieved by comparing biological and behavioural measures of a release vervet group with indigenous vervet control groups inhabiting the same anthropogenically modified landscape, within the same time period.

Data were collected on two habituated control groups of vervet monkeys over a 24-month observation period inhabiting an anthropogenically modified habitat in Kenya. In addition, data were collected over a 20-month pre- and post-release monitoring period on a group of released vervet monkeys, subjected to a rehabilitation release. Datasets included habitat assessments, behavioural ecology, survivorship and social networks. The control data were used to inform release site selection and provided comparable datasets against which the post-release monitoring data could be compared to assess release success.

The analysis of the release site selection process indicated that habitat assessments do not provide sufficient detail to be the only selection tool and need to be conducted alongside a minimum one-year food availability study. The behavioural ecology of the control vervet groups showed trends representative of other vervet groups living in anthropogenically modified habitat. Using the control groups behavioural ecology as a unique set of indicators and criteria against which the release group could be monitored, proved to be invaluable. The release was deemed successful due to Release groups survivorship, activity budgets and general feeding ecology falling within the expected ranges set by the control groups. Social network analysis revealed that extended periods of captivity, where new infant individuals are introduced over time, could benefit group cohesion and ultimately post-release survival.

The findings of the study indicate that wild-born, rehabilitated vervet monkeys can be successfully returned into the wild, in close proximity to wild conspecifics. It is hoped that future translocations will follow a similar process of comparing biological and behavioural measures between indigenous control groups and newly released groups. Future translocations can benefit from the knowledge gained during this rehabilitation release, and each newly monitored and reported translocation will add vital information to the developing primate translocation model.