Penning prior to release decreases post-translocation dispersal of jewelled geckos

Abstract

Translocation is an essential conservation tool often used to re-establish reptile populations following anthropogenic extirpation, but is not always successful. One factor potentially limiting success is dispersal of individuals from the release site immediately after translocation and consequent non-overlap of ranges. 'Penning' involves the use of an enclosure to restrict dispersal of translocated animals for a pre-determined period of time, with the aim of habituating animals to the release site so that they will establish a breeding population. We evaluated the utility of penning for limiting post-translocation dispersal of jewelled geckos (Naultinus gemmeus) by simultaneously tracking 19 geckos that had either been translocated into a pen for 9-10 months prior to the pen's removal (n=10) or were translocated to a nearby site with no physical barrier to dispersal (n=9) over a 3-week period. The area occupied by penned geckos did not increase following removal of their pen, despite suitable habitat being available outside the pen area. In contrast, un-penned geckos moved distances of up to 40m outside of their release area, and effectively increased the area that they were occupying as a group 4.4-fold over the 3-week period. We suspect that when Naultinus geckos are released without time in a pen, some individuals may disperse too far to contribute to a breeding population and, consequently, the likelihood of population establishment and rate of population growth may be diminished. Our hypothesis is supported by a survey we conducted the following summer in which all four adult female geckos found at the penned site were gravid, but neither of the females resighted at the un-penned site was gravid. We believe that the potential advantages of penning (e.g. restricting initial dispersal, increased ease of monitoring) may outweigh the disadvantages (e.g. cost) for many herpetofauna translocations.