The effect of pre-release captivity on the stress physiology of a reintroduced population of wild eastern bettongs

Stress is important in reintroduction biology because it can influence mortality, dispersal and recruitment and determine establishment success. As stress is unavoidable during reintroduction, it requires deliberate management. Release tactics (e.g. ‘delayed- and immediate-release’) are often selected specifically based on their presumed effect on physiological stress, yet, the actual physiological effects are seldom tested. Delayed-release involves pre-release confinement (in situ), or captivity (ex situ), which can improve post-release performance in some cases, or induce a detrimental effect in others, especially in wild animals. Quarantine is another common pre-release practice that requires captivity/confinement carrying similar post-release physiological implications. We use faecal glucocorticoid metabolite concentrations (FGM) to evaluate how a delayed-release involving 95–345 days in captivity influences the stress physiology of wild eastern bettongs (Bettongia gaimardi), compared to an immediate-release (within 24 h of capture), across the initial 18 months post-release. The results suggest that FGM concentrations were relatively higher in the delayed-release group at release, but significantly lower after ca. 2 months of release. We assessed seasonal fluctuations in FGM concentrations, the effect of release tactics on in-trap behaviour, and the relationship between those behaviours and FGM concentrations. We found that FGM concentrations fluctuated seasonally, but release tactics did not influence behaviour, and that behavioural variations had no relationship with FGM concentrations. Overall our results, coupled with previous research, suggest that an immediate-release is preferable when quarantine is not required.