Use of wild–caught individuals as a key factor for success in vertebrate translocations

Success of vertebrate translocations is crucial to improve efficacy and efficiency of conservation actions but it is often difficult to assess because negative results (failed translocations) are seldom published. We developed surveys and sent them to heads of conservation services in three major Spanish Mediterranean regions. The purpose of our surveys was to determine which methodological factor, that could easily be implemented in practice, was more influential for translocation success. These factors included the origin of translocated individuals (captive or wild) and translocation effort (propagule size and program duration). After analyzing 83 programs, corresponding to 34 different vertebrate species, by means of generalized linear mixed modelling, we found that 'origin' was more relevant for translocation success than 'effort', although we could not rule out some role of translocation effort. Variance in success of translocation programs involving individuals from wild sources was smaller and consequently results more predictable. Origin interacted with taxa so that success was higher when using wild birds and especially wild fish and mammals, but not when releasing reptiles. Hence, we suggest that, for any given effort, translocation results will be better for most vertebrate taxa if individuals from wild sources are used. When this is not feasible, managers should release captive-reared individuals for a long number of years rather than a short number of years.