Predicting reintroduction costs for wildlife populations under anthropogenic stress

Abstract

Abstract In conservation decision‐making, it is important to have information not only on the likely effectiveness of conservation actions, but also on the corresponding costs. Reintroduction of wildlife is a commonly applied ‘last resort’ conservation measure. However, a quantitative approach to predict the costs of reintroduction for sustaining a wildlife population under the influence of time‐varying anthropogenic stress is lacking. Here, we fill this gap by quantifying the costs of reintroduction as a function of exposure to an environmental stressor and the size of the wildlife population to be maintained. Our approach combines quantitative stressor–response relationships for vital rates (reproduction and survival) with a wildlife demographic model to compute the impacts of the stressor on the size of the target population. Subsequently, cost estimates are obtained by quantifying the number of captive‐reared individuals needed per year in order to maintain a user‐defined population size, given the exposure to the stressor of concern. We applied our approach to calculate the reintroduction costs required to restore a minimum viable population (MVP) of peregrine falcons (Falco peregrinus) in California over the period 1970–1994, when the population was exposed to the toxicant dichlorodiphenyldichloroethylene. Assuming a gradual yearly increase of 150% in the availability of captive‐reared young, 1,753 captive‐reared young were required to restore and maintain a MVP of 238 adults. The corresponding reintroduction costs were in total ~$3,023,000. Assuming lower reintroduction efforts (in terms of the availability of captive‐reared young), the projected reintroduction costs decreased by ~33%. However, the population then reached the minimum viable size only 9 years later, thus reflecting a trade‐off between costs and population viability. Synthesis and applications. The approach presented in this study ensures an adequate prediction of the costs of maintaining a wildlife population at a user‐defined size through reintroduction. It can be applied to any wildlife population in order to obtain the number of individuals and corresponding costs required to sustain a population under current and future influence of an anthropogenic stressor. This type of information provides important input for decision‐making necessary to conserve biodiversity.