Taking control of risky decisions in endangered species conservation

In our case study on the critically endangered Mauritius olive white-eye Zosterops chloronothos, we demonstrated how difficult decisions about ongoing support of actively managed species can be approached by carefully combining experiments and risk analysis (Ferri ere et al., 2020). The thoughtful commentaries by Converse & Sipe (2021) and Stojanovic & Crates (2021) offer opportunities for further insights. When we conceived the study described in Ferri ere et al. (2020), the conservation management we were carrying out for the olive white-eye had become unsustainable. Adding more feeding stations would exceed staff capacity and budget. It became clear that if, as we believed, supplemental feeding was essential for the population to grow, we had to find a way to make the workload sustainable, as well as finding a potential long-term minimal management strategy. This should be the aim of most conservation projects which are limited by funding and must look for ways to reduce project costs without jeopardizing species recovery; that is, to find a solution to what is often believed to be a zero-sum game as described by Converse & Sipe (2021). Facing this problem, we turned to the experiences of managers elsewhere in the world who dealt with similar issues for similar species. In particular, the solution to our problem was inspired by those used to help the recovery of the hihi Notiomystis cincta in New Zealand (Chauvenet et al., 2012). In our case, our experimental approach was limited by uncertainty and our willingness to take calculated risks. We were unable (and unwilling, see below) to use a control group with no feeding, because we felt the risk to the population and the species would be too great; although the Ile aux Aigrettes population is increasing, the one on mainland Mauritius is still decreasing (Maggs et al., 2015). Moreover, previous experiences suggest that some drastic management decisions can have immediate impacts (Armstrong, Castro & Griffiths, 2007). A catastrophic decline in the population might leave us no time to react. Therefore, we had to get our decisions right; a trial might help, but within limits. By creating alternatives, articulating uncertainty and clearly recognizing our objectives, including how we see benefits and risks, we effectively embraced those limitations, took control of the decision process and made room for success (Converse & Sipe, 2021). Our approach in Ferri ere et al. (2020) underlines two key steps for success in changing a conservation management strategy, which highlight both the challenges and opportunities pointed out by Converse & Sipe (2021) and Stojanovic & Crates (2021). The first step was to think openly about uncertainty. Endangered species may face a wide variety of interacting threats. Small populations also mean small sample sizes and greater chances of extreme events, making inference difficult, compounded by species traits that reduce observability. We were able to monitor our study species closely, thanks to well-known territories and previous ringing efforts. As Stojanovic & Crates (2021) point out, other programs may not have such advantages; however, when uncertainty is high, learning can be harder (e.g. if there are multiple confounding factors) but it may also be easier (e.g. if it is easier to shift current beliefs). In such cases it is even more critical to articulate uncertainty very clearly: where does it come from, how does it affect our decisions, how can we reduce it? This can be a fundamental challenge to the assumption, often implicit in conservation, that more data are always better. A useful method we increasingly turn to for decisions on monitoring is calculating the value of information provided by more data (Canessa et al., 2015; Canessa et al., 2020). The second vital step was to be clear on how we felt about uncertainty. We agree with Stojanovic & Crates (2021) that risk aversion is common in conservation programs, but it is not in itself irrational, particularly where worst-case scenarios may involve the extinction of an entire species. In our case, ongoing vegetation restoration efforts and our ability to closely monitor the species, and respond if necessary, led us to believe that even worst-case outcomes would not be as catastrophic as in an immediate crisis phase (Stojanovic & Crates, 2021). Given worse possible