Optimizing the use of endangered species in multi-population collection, captive breeding and release programs

Abstract

Evaluating the spectrum of risks and rewards of captive breeding and release is central to identifying responsible conservation actions for declining species. Trade-offs among source, captive, and target wild populations are expected when optimizing the use of the last few remaining individuals of a population. Yet few analyses are conducted to optimize the choice of source population from which animals are collected and released. Using linked scenarios, we evaluated the risks and rewards of collection, ex situ rearing, and release of endangered Greater Sage-grouse in Canada. We integrated demographic rates from captive populations with wild population abundance, demography, and habitat relationships in a spatially explicit individual-based model framework for multiple populations across national and international borders. We quantified the potential for released birds to improve wild abundance and reduce extinction risk in two target wild populations. To gain general insight, we compared risks and rewards among different source and target population sizes and trajectories. The risks caused by removing individuals from the wild depended on the number of animals removed, and source abundance and trajectory, and were partially obscured by stochasticity. Releases into small and rapidly declining populations provided the greatest near-term reductions in extinction risk, but improvements were short-term. Yet releases into larger and more stable populations resulted in longer lasting conservation benefits than in more vulnerable populations but required greater initial release effort. Systematic modeling approaches that evaluate a spectrum of trade-offs and quantify conservation risks and benefits can help direct the expectations and effort invested in captive breeding and release programs.