Can reintroductions to degraded habitat succeed? A test using the common brushtail possum

Habitat degradation contributes to species decline, and habitat quality is an important factor influencing reintroduction success globally. Habitat quality can include a range of physical resources such as nest sites and food resources but also anything that can restrict the use of these resources such as predation risk or competition. In arid Australia, introduced predators are thought to be the primary cause of mammal extinction and reintroduction failure although habitat clearance and alteration are also major causes of population decline. Common brushtail possums are one arid Australian marsupial close to regional extinction. To understand whether habitat quality was limiting their recovery, we reintroduced 148 possums into an area where introduced red foxes were controlled but historic overgrazing had degraded the habitat. We measured both direct (hollow availability, midstorey cover and high-quality plant foods) and indirect (survival, condition, reproduction, movement) measures of habitat quality. Sixty-seven released possums and 26 post-release recruits were radiocollared for up to 2 years after release. Post-release survival of radiocollared possums was high after 12 months (0.70), and there were no deaths from starvation. Predation by feral cats was the most common cause of mortality, and the open, degraded habitat may have exacerbated predation risk. Continuous breeding, good body condition and comparative home ranges with other sites suggested that food resources were not limiting. Possums used natural tree hollows inEucalyptusspp. with no use of artificial nest boxes. Results suggest that historically degraded habitat was not a barrier to short-term reintroduction success when foxes were controlled and natural tree hollows were plentiful. However, demographic data on hollow-bearing tree species suggest a possible future decline in availability of hollows. These factors, combined with the unknown effects of drought, and synergistic effects of predation and poor quality habitat, suggest long-term reintroduction success may require improved habitat and cat control.