Are subadult dispersers at high risk of mortality in translocated populations? A case study from a threatened mesopredator

Abstract

Natal dispersal and survival are the primary means of population expansion in reintroduction projects, but few projects intensively monitor the offspring of released individuals. Subadults may differ from adults in their susceptibility to threats or their habitat requirements which may require alternate management strategies. We investigated survival rates, habitat use and shelter site choice during natal dispersal in reintroduced western quolls (Dasyurus geoffroii). We compared data previously collected on the first cohort of subadults born to founders (n = 17) with subadults from an established cohort 6 years after release (n = 22). Subadult quolls were radiotracked after weaning to monitor survival and habitat use and the effects of sex and size on mortality, dispersal distance, habitat selection and shelter choice were investigated in the established cohort. We confirmed high survival with no confirmed deaths among the established cohort and only two confirmed deaths among F1 founders (12%) during the 26 weeks of monitoring. All individuals remained within the area where introduced predators, a key threat to quolls, were intensively managed through aerial baiting. Males dispersed significantly further than females, with consistent outward expansion of up to 13‐km and increased movement between shelter sites occurring between mid‐December and early‐February. During dispersal, both sexes displayed a similar preference for woodland habitats and avoidance of open areas to adult quolls. The founding cohort primarily used rabbit warrens as shelter sites, whereas the established cohort after release used more hollow logs and tree hollows. This change may indicate gradual selection towards these safer shelter sites and filial transfer of this preference to offspring. Monitoring subadult movement, mortality and habitat use is integral to determining population viability and the effectiveness of management actions in reintroduction programs.