Reintroduction or natural colonisation? Using cost-distance analysis to inform decisions about Rodrigues Island Fody and Warbler reintroductions

When making decisions about reintroducing a species, practitioners need to consider whether the release site contains habitat suitable for those species, whether past extinction drivers have been remedied and whether reintroduction is the best option for the species to recolonise the release site. These concerns are captured within two paradigms; the habitat and metapopulation paradigms. We use cost-distance analysis to assess the need for reintroduction of two bird species, Rodrigues Fody and Rodrigues Warbler, to Anse Quitor reserve on Rodrigues Island, testing hypotheses based on these underlying paradigms. Given a lack of detailed field studies of dispersal across the landscape on either species we rely on expert judgement. Our results show that experts believe Rodrigues Fody will naturally colonise Anse Quitor but that Rodrigues Warbler may not, at least within a time frame of 10 years. This information and treatment of expert judgement allows greater justification in reintroduction planning. Our method shows one way to assist in reintroduction decision making in poorly studied systems.