Code and Data for "Social composition of soft-release groups is correlated with survival of translocated gopher tortoises"
The social structure of translocated animal populations can have important effects on the survival and reproduction of translocated individuals for both solitary and social species. The gopher tortoise (Gopherus polyphemus) is a reptile of conservation concern that is currently experiencing tremendous levels of mitigation translocation in Florida, USA. Individuals live in aggregations of burrows with frequent agonistic, courtship and burrow-sharing interactions between residents. Given that exposure to many unfamiliar individuals may increase the frequency of aggressive interactions and social stress following translocation, we predicted that tortoises with greater numbers of familiar individuals co-translocated from the same origin site would have higher survival after translocation. To test this, we updated a recently published survival analysis of 2,822 translocated tortoises and 502 identified carcasses from a translocation site in the western Florida panhandle from 2006 – 2022 (Loope et al. 2024a. Animal Conservation 27:685-697). Accounting for the number of potentially familiar individuals improves the model and increasing this value reduces the probability of being found dead, while controlling for simultaneous effects of soft-release enclosure identity, release season, release density, region of origin, sex and size. This effect is modulated by release density and is only strong when density is high, suggesting a role for social interactions. This effect is present only in the first few years after release, prior to the removal of soft-release enclosures preventing dispersal and is similar in magnitude to previously identified effects of density, release season, and region of origin. We suggest that this effect may result from reduced aggressive interactions or social stress for tortoises with a greater number of familiar individuals in their release enclosures but cannot rule out the possibility of reduced novel pathogen exposure for individuals released with a greater number of individuals from the same source site, or other factors that may be confounded with the size of translocated groups. Designing and implementing mitigation translocations to account for social composition of gopher tortoise groups could improve survival in release enclosures.