Rapid post-release adaptation of released orphan elephants from a rescue centre to a national park in Sri Lanka based on faecal glucocorticoid metabolite analyses

Rewilding and species reintroductions are increasingly important conservation strategies, involving both captive-bred and wild-rescued animals, with the goal of restoring ecosystems and supporting populations of threatened species. Over the past 30 years, the Elephant Transit Home in Sri Lanka has rescued and rehabilitated more than 150 orphaned elephant calves that were subsequently released back into the wild. Understanding how rehabilitation and release processes affect the welfare status of these calves can provide valuable information on factors affecting release outcomes. This study evaluated patterns of faecal glucocorticoid metabolite (fGCM) concentrations as a physiological indicator of stress in 10 orphaned elephants (six males, four females) rescued at ≤1 year of age and released back into Udawalawe National Park after rehabilitation at the Elephant Transit Home (release age, 6 to 8 years). Faecal samples (~2/week) were collected for 9 months pre- (<i>n</i> = 53 samples) and 16 months post- (<i>n</i> = 153 samples) release. Mean fGCM concentrations during the early post-release period (first 17 days) were significantly higher than in pre- and later post-release periods, with no differences between males and females. Results indicate elephants adapted quickly after release, likely aided by being released in a small group (<i>n</i> = 10) of socialized cohorts. In fact, fGCM normalized to concentrations lower on average than at the Elephant Transit Home in the months preceding release. Understanding the stress response of elephants during and after translocations is crucial for well-being and successful integration into the wild. Minimizing stress through appropriate protocols, such as selecting strong social units, is essential. Hormonal monitoring is a valuable tool that should be considered long-term to assess the adaptation, survival and eventual reproductive success of rewilded elephants.