Use of simulation models to plan species reintroductions: the case of the bearded vulture in southern Spain

Abstract

I used VORTEX to make a prior evaluation of the planned reintroduction project of the endangered bearded vulture (Gypaetus barbatus) in the mountains of southern Spain. The minimum size of a captive population needed to ensure the release of two bearded vulture fledglings per year is 30 individuals. If breeding success was improved, this minimum captive population could be reduced to 10 individuals. As the cost of the project is proportional to the size of the captive population, some research effort should be devoted to improving breeding success in captivity. The current size of the captive population — four individuals — is not enough to start the releases, even if the vultures were already breeding. The first step for the project should be to increase the size of the captive population. If on average one individual per year was added to the captive population, it would take 15 years to reach 30 individuals. If breeding in captivity was improved, it would take only three to seven years to reach the minimum captive population of 10 individuals. Once releases were started, the project would need on average 20 years to reach a goal of 15 adult pairs in the Cazorla mountains. Both the success of the project and the time necessary to reach this stated goal are very sensitive to the mortality rates in the wild. There is little known about these rates, and better estimates are urgently needed to improve the predictions of the models.