Soft-release versus hard-release for reintroduction of an endangered species: an experimental comparison using eastern barred bandicoots (Perameles gunnii)

Abstract

Context Reintroduction is a popular tool for conserving endangered species, yet many attempts fail. Soft-release measures, including acclimatisation, have been used for many species around the world, based on the reasoning that gradual and supported reintroductions should improve the success of animals released into an unfamiliar wild environment. However, experimental testing of soft-release methods is rare. Aims To experimentally test the effect of a soft-release method versus a hard-release method on the initial reintroduction success of the eastern barred bandicoot (Perameles gunnii). Methods We released 12 captive-bred eastern barred bandicoots into a predator-proof reserve using two methods: soft-release (7 days of on-site acclimatisation with supplementary food before release) and hard-release (no acclimatisation and no supplementary food). We monitored the bandicoots intensively via radio-tracking and live-trapping for 4 weeks after release. Compared with hard-release bandicoots, we predicted that soft-release bandicoots would have (1) reduced movement (first night dispersal, site fidelity and activity range), (2) more directed patterns of habitat selection, (3) improved bodyweights and (4) improved survival. Key results There was no detectable difference in habitat selection, overall weight change and survival between the soft-release and hard-release groups. There was moderate evidence that, compared with the hard-release group, soft-release bandicoots moved less, demonstrated lower individual variation in all measures of movement, and lost weight more gradually after release. In most cases, effect sizes were moderate to large but had large standard errors owing to both small sample size and high variance. Consequently, statistical testing failed to detect significant differences at the 5% level. Conclusions Despite evidence that the release method influenced some of the monitored behaviours, soft-release did not confer a consistent and substantive advantage for captive-bred eastern barred bandicoots at our site. We conclude that soft-release is unlikely to improve overall reintroduction success for this species at fenced predator-free sites. Implications The present study suggests that the preferred option for reintroductions of eastern barred bandicoots to fenced sites is a hard-release, information that is now being used to guide reintroductions of this species. Similar experiments should be undertaken to improve reintroduction practice for other endangered species.