Glucocorticoid Metabolites and GPS Radio Collar Telemetry in Wildlife Conservation: The Jane Goodall Institute Mandrill Release Project in the Republic of Congo

Abstract

Wildlife populations are being depleted globally by pressures associated with the growing human population and non-human primate populations are in sharp decline. The Tchimpounga Chimpanzee Rehabilitation Sanctuary in the Republic of Congo cares for orphaned primates with the goal of reintroducing them to the wild when appropriate. The primary aim of this study was to reintroduce the mandrills held at Tchimpounga into Conkouati-Douli National Park following the International Union for Conservation of Nature (IUCN) Guidelines as closely as possible. In preparation for the release we built an enclosure at the selected release site and tested the global positioning system (GPS) collars the animals would be wearing. At the end of the study we retrieved the GPS collars and found fewer successful fixes than expected and analysed the collar fix success rates in relationship to each individual’s use of three-dimensional space and mass in an effort to understand the lack of successful fixes. We found that vegetation density and collar height within the vegetation significantly affected fix success rates. Our post-release data indicated larger animals spent more time on the ground than smaller animals, and that smaller animals had more successful fixes. We found variation in GPS collar function and that how the animals interact with their three-dimensional (3D) environment affects collar function. If animals in a study group spend different amounts of time at different heights in the forest it could bias the data. Researchers should thus test the collars they will be using for height bias in circumstances where the release subjects have a 3D relationship with the environment around them. We recommend accounting for an animals’ use of three-dimensional space in GPS collar studies where the species is not fully terrestrial and vegetation, topography, or human-made structures are likely to interfere with their collars’ access to satellites.
We also used non-invasive faecal sampling to measure the mandrills’ glucocorticoid metabolite levels as a biological proxy for their stress response to each stage of the release. The findings suggest that faecal glucocorticoid metabolites can be used to capture the biological response to the stages of reintroduction. All mandrills had an increase in glucocorticoid metabolite values post transfer. It took 4 weeks for the glucocorticoid metabolite values to decrease although there was variation amongst individuals. We recommend using faecal glucocorticoid metabolite analysis in release projects to inform decisions about how long the study species should be held in a pre-release enclosure to overcome the stress of transfer and habituate to their surroundings prior to being released. The findings of this study also highlighted that different animals reacted differently to the stages of the release process, thus researchers should assess animals as individuals rather than a group to assure maximum animal welfare through the release process.
Ultimately, through scientifically testing aspects of this release project we gained insight to inform future mandrill releases as well as wildlife release projects generally. We recommend GPS collars are tested in the release area and the results are reviewed prior to fitting the collars to the animals. GPS collar studies should account for an animal’s 3D relationship with topographical obstruction and vegetation within their environment because systematic differences in forest usage can bias collar data. Finally, we recommend sanctuary release projects use soft release methods unless hard release had been thoroughly validated for the species under representative circumstances.