Testing restocking methods for an endangered species: Effects of predator exclusion and vegetation cover on common hamster (Cricetus cricetus) survival and reproduction

Animal restocking is a widely used conservation tool to restore relict populations of endangered species. However, success of such operations is often low due to poor short-term survival and experimental evidence is required to improve restocking results. We tested the impact of different release conditions on survival and reproduction of captive bred common hamsters (Cricetus cricetus L. 1758), a highly endangered species in Western Europe. As predation plays a determinant role for released hamsters, especially during the first days after restocking, we performed two release experiments intending to reduce mortality: we tested (1) the efficiency of terrestrial predator proof electric fences and (2) the impact of improved shelter availability. We assessed both survival rate and reproductive success by radiotracking 70 hamsters between release date and the end of their aboveground active period. Reducing contact between released animals and predators thanks to electric fences had a strong positive impact on hamsters’ survival and allowed them to have enough time to reproduce. It also appeared that release of hamsters was more efficient in wheat crop than in alfalfa. As expected, wheat harvest, inducing a sudden lack of shelter, negatively impacted restocking success. Finally, lifetime after release affected the number of litters per female and varied with individual characteristics: it decreased with burrow change frequency and was slightly lower for males. We conclude that electric fences associated with permanent well-developed vegetative cover like unharvested wheat seem to be suitable for releasing hamsters.