Predicting reintroduction costs for wildlife populations under anthropogenic stress.
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.