Reintroduction and reinforcement as conservation strategies for the Southern Ground Hornbill Bucorvus leadbeateri: a model-based evaluation

Abstract

Reintroduction and reinforcement of threatened free-ranging wildlife populations are commonly used conservation strategies. Reintroduction involves releasing individuals or groups into suitable unoccupied areas, while reinforcement involves releasing individuals or groups into existing depleted populations. Understanding the life history, behaviour, reproduction and genetic structure of the target species helps ensure the success of reintroductions. We modelled the efficacy of reintroducing different numbers and sexes of founders into areas with varying numbers of vacant territories, both with and without population reinforcement, as a conservation tool to enhance population growth in the long-lived, co-operative breeding Southern Ground Hornbill Bucorvus leadbeateri. Based on our current knowledge of the biology of the species, and the fitness of released individuals, we demonstrate that a reintroduction programme is only likely to reduce, and reverse, population declines of the species when combined with a reinforcement programme, but that neither reinforcement nor reintroduction alone will reduce the decline. We suggest that releases of such long-lived species can only reverse the population decline if carried out over long periods (i.e. several generations/decades) and in core areas of at least 20 groups to ensure metapopulations that will be self-sustaining and avoid inbreeding. This can mean high operating costs for reintroduction programmes with the added challenge of long-term commitment and support from landowners, NGOs and sponsors. This supports management decisions to choose reintroduction core areas that naturally link to wild populations to reduce the need for ongoing reinforcement.