Animal Reintroductions: An Innovative Assessment of Survival

In an effort to help bolster ecosystems and species struggling to survive, scientists use a variety of tools to help species rebuild. However, success with relocation, repatriation, translocation, and reintroduction programs is still varied. In this study, researchers attempt to show how quantitative measurements of reintroduction can help to evaluate the success or failure of programs aimed at helping species survive and thrive, using tadpoles and toads in the Rocky Mountain National Park as a case study.

Different methods of reintroduction for species at risk of survival have been used over the past few decades, but most programs are not successful. “Reintroduction efforts for birds, mammals, and fish are deemed successful less than 50% of the time,” the authors of this study note, while “reintroduction efforts for amphibians and reptiles reflect similar results.” The researcher say that when it comes to the “stakes” of reintroduction, they can be both biological (the extinction of a species) as well as financial (programs are expensive to implement, and their value is questioned if they don’t succeed). “Success depends on multiple factors, including habitat quality and the number of individuals that are released, and many of these attributes or characteristics can be quantified, allowing for an evaluation of effort,” they say. But despite the need for sober analysis of programs and their efficacy, “evaluations of reintroduction efforts are uncommon.”

To try to address this gap in evaluation, the authors of this study set out with the goal of describing the progress of a reintroduction effort of tadpoles and toads in the Rocky Mountain National Park. They did this “not to declare success or failure”, which they said they “cannot do at this point in the reintroduction program,” but instead to outline ongoing challenges and understand how to strengthen the program. Based on current and past numbers, they noted that “in our best year, we estimated that 48% of tadpoles survived to metamorphosis.” They observed that “the highest survival probabilities [happened] in the year with the largest number of released tadpoles, suggesting that density-dependent processes may not be operating, at least for the cohort sizes in our study.” They concluded that overall, it was better to release metamorphosed toads rather than tadpoles. “The fewer days spent at the site as a tadpole, the higher survival probabilities.” According to their findings, the “most critical” aspect of the reintroduction was the “recruitment of breeding adults into a population.” Without adequate recruitment, they say “there is little chance of establishing a self-sustaining population.”

Apart from these findings of this particular case study of tadpoles and toads, the researchers kept in their mind the bigger picture of reintroduction programs in general. In their conclusion, they state that “commitment to reintroduction programs is required at multiple fronts including the acquisition of raw materials, logistical planning, and support (funding). Data that can inform each of these efforts and thus guide commitments is critical.” They note that evaluating programs on an ongoing basis is vital to the project’s success, as “interim information promotes realistic expectations for the program, informs the level of commitment necessary to reach the endpoint of a self-sustaining population, and can be calculated in terms of both cost and time.” The value of long-term monitoring in tandem with releases cannot be underestimated. For animal advocates interested in wildlife issues this is important information to keep in mind, and might guide how advocacy for different at-risk species is carried out over time.

Original Abstract:
Quantitative evaluations of reintroductions are infrequent and assessments of milestones reached before a project is completed, or abandoned due to lack of funding, are rare. However, such assessments, which are promoted in adaptive management frameworks, are critical. Quantification can provide defensible estimates of biological success, such as the number of survivors from a released cohort, with associated cost per animal. It is unlikely that the global issues of endangered wildlife and population declines will abate, therefore, assurance colonies and reintroductions are likely to become more common. If such endeavors are to be successful biologically or achieve adequate funding, implementation must be more rigorous and accountable. We use a novel application of a multistate, robust design capture–recapture model to estimate survival of reintroduced tadpoles through metamorphosis (i.e., the number of individuals emerging from the pond) and thereby provide a quantitative measure of effort and success for an ‘‘in progress” reintroduction of toads. Our data also suggest that tadpoles released at later developmental stages have an increased probability of survival and that eggs laid in the wild hatched at higher rates than eggs laid by captive toads. We illustrate how an interim assessment can identify problems, highlight successes, and provide information for use in adjusting the effort or implementing a Decision-Theoretic adaptive management strategy.