Conservation translocations in urban environments: State of the knowledge and future directions

Cities are important for biodiversity conservation and are a central focus in the United Nations Decade of Ecosystem Restoration. Species reintroductions and population reinforcements (i.e. conservation translocations) are an important component of conservation, yet are rare in urban environments, possibly because of perceived risks in highly modified and complex social-ecological urban systems. Here we review the literature describing urban conservation translocations to provide guidance for their effective implementation. We find that urban translocations have been performed for a variety of aims including focal species conservation, improvements in ecosystem functions in the later stages of restoration projects (e.g. seed dispersal in revegetated sites) and for site remediation (e.g. organic pollution removal), and enhancing human-nature connections. Conservation translocations were found in a range of urban habitat types including formal and informal greenspaces, grey spaces, streams, ponds, and marine environments, ranging from near-historic conditions (e.g. remnant/restored sites) to highly modified novel/designed systems. Barriers and enablers varied between terrestrial and aquatic release sites, with predators, habitat suitability, and leaving release sites being more important in terrestrial sites and disturbance (flooding) regime and pollution being more important in aquatic sites. A range of techniques have been applied to mitigate these barriers. Success rates in urban translocations are high (>90 %) and comparable to conservation translocations in general, suggesting they can contribute to urban biodiversity conservation by assisting species to overcome dispersal barriers and occupy otherwise suitable urban habitats. However, evaluation methods vary widely between urban translocation studies. There is also a need for longer-term monitoring of translocation success that might be achieved simultaneously while enhancing human-nature connections through citizen science programs.