Conservation translocations and post-release monitoring: Identifying trends in failures, biases, and challenges from around the world

In an attempt to slow or reverse the loss of biodiversity, conservation translocations have been implemented to restore wild populations of dwindling or extirpated species and have increased concurrently with multiplying threats to biodiversity. Here, we reviewed 554 translocation case studies from around the world in an effort to assess how frequently studies monitor populations post-translocation, and if performed, for what length of time monitoring was done. Our secondary objectives included investigating shifts in reintroduction research trends, including whether species of certain conservation statuses (global and local) were more likely to be subjects of translocation efforts, the factors cited as reasons for initial species declines, and the causes of failed translocation attempts. We found that the majority of studies conducted post-release monitoring for a period of 1-4 years, and the highest proportion of failures occurred within the first four years. Overall, the most important factor contributing to failure was the causes of initial decline of the species, and there was no evidence that success rates have increased over the past decade despite increasing knowledge in the field. Many translocations were focused on locally extirpated species that had low risk of global extinction, especially in North America, Europe, and Oceania. The driving forces of failed translocations varied with predation, management issues, and habitat factors as common challenges. Future programs should focus on addressing the initial cause of decline and ensure that resources are in place to support a minimum of four years of post-release monitoring to help ensure a successful outcome.