alexa Assessing the efficacy of reintroduction programmes by modelling adult survival: the example of Hermann's tortoise
Environmental Sciences

Environmental Sciences

Journal of Biodiversity & Endangered Species

Author(s): A Bertolero, D Oro, A Besnard

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Although reintroduction programmes are often implemented for recovering animal populations, projects seldom monitor the long-term survival of released animals. In addition, although many releases may occur in the same area, little is known about how the survival of successive release batches is affected by the presence of conspecifics and density dependence. Here, we use multi-state capture–recapture modelling (combining information from recaptures and recoveries) to analyse the survival of two batches of Hermann's tortoise Testudo hermanni hermanni released in a 10-year interval and monitored for 18 years at the Ebro Delta (western Mediterranean). We also tested whether the released animals experienced lower survival (i.e. a release cost) before becoming familiar with the new environment. Although we used a hard-release method, neither group experienced a short-term release cost. Annual survival of both groups differed and was not negatively affected by density-dependent factors. Annual survivorship of the first group of released tortoises was constant and very high (0.945, se=0.011), and similar to that estimated from several natural populations. The presence of a terrestrial predator in 1 year (before the release of the second group) significantly decreased the survival of tortoises (0.819, se=0.073). Strikingly, survival of the second batch was significantly lower than that of the first group after the first years of release (0.775, se=0.049). Although survivorship for the first group suggested that habitat quality was high, the second group seemed not to acclimate well to the new environment, possibly due to the presence of resident tortoises. From a management perspective, reintroduction programmes of the Hermann's tortoise are a successful strategy for its recovery. Nevertheless, it seems advisable to avoid: (1) the release of tortoises at the core of well-established populations and (2) areas with a high density of predators, which can jeopardize the reintroduction success, especially when the number of released individuals is small.

This article was published in AnimConserv and referenced in Journal of Biodiversity & Endangered Species

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