Translocating ratsnakes: Does enrichment offset negative effects of time in captivity?

Context Wildlife translocation is a conservation tool with mixed success. Evidence suggests that longer time in captivity may negatively affect an animal's post-release behaviour and survival. However, environmental enrichment may reduce the deleterious effects of captivity for animals that are going to be released into the wild. Aims The aim of the present study was to compare first-year post-release survival and behaviour of translocated ratsnakes (Pantherophis obsoletus) held captive for varying durations (1-7 years) either with or without enrichment, with that of resident and wild-to-wild (W-W)-translocated ratsnakes. Key results Being in captivity before release negatively affected survival; 11 of 19 (57.9%) captive snakes died or were removed from the study within 12 months, compared with 3 of 11 (27.3%) resident snakes and none of five (0%) W-W snakes. Furthermore, survival probability declined the longer a snake had been in captivity. Six of the seven snakes (86%) that we released that had been in captivity for four or more years before release died during this study, regardless of whether they were enriched or not. Although W-W-translocated ratsnakes moved more often and further than did snakes in other groups, this difference was apparent only in the first month post-release. We found no evidence that abnormal movement patterns or winter behaviour was the cause of reduced survival for captive snakes. Instead, our data suggested that spending time in captivity reduced concealment behaviour of snakes, which likely increased the vulnerability of snakes to predators. Captivity also compromised the foraging ability of some of the snakes. Although there were no overall differences in percentage weight change among the four groups, two snakes (one enriched, one unenriched) were removed from the study because of extreme weight loss (>30%). Conclusions Our results suggested that environmental enrichment did not offset the negative effects of captivity on ratsnakes and that the likely mechanism responsible for low survival was vulnerability to predators. Implications Whether extended periods in captivity render other species unsuitable for translocation, how long it takes for captivity to have deleterious effects, and whether environmental enrichment is also ineffective at offsetting captivity effects in other species remain to be determined.