An Assessment of Mitigation Translocations for Reptiles at Development Sites

All native reptile species are protected against harm through their inclusion on UK legislation. With the exception of two species, this protection does not extend to reptile habitat. As a result, reptiles are frequently subject to mitigation translocations to facilitate the development of land. However, there are few published studies of the effects of mitigation translocation on reptile populations and whether such translocations are effective conservation interventions. The effectiveness of translocation was tested through a combination of: 1) field surveys of sites subject to mitigation across England and Wales; 2) the radio tracking of translocated adders; 3) the monitoring of a population of slow-worms at site where they were released 20 years ago; and 4) a penning experiment to test whether viviparous lizards attempt to disperse from the release site. Very few translocated reptiles were encountered during the monitoring of release sites. This paucity of recaptures is either due to post-release mortality, imperfect detection or dispersal. Translocated male adders dispersed farther and had larger home range sizes than resident conspecifics. Some male adders undertook large unidirectional migrations back to the donor site crossing areas of unsuitable habitat as they did so. A population of slow-worms persisted at an isolated site two decades after translocation, albeit in relatively small numbers. Body condition improved over 20 years and the population resumed breeding and recruitment. The temporary penning of viviparous lizards was effective in preventing post-release dispersal and resulted in an increase in recapture rates of greater than 16 times when compared to unpenned viviparous lizard populations. The fact that no lizards were recaptured in the unpenned areas provides strong evidence for the effect of post-release dispersal. Although, mitigation translocations may prevent the immediate death of animals that would otherwise be destroyed with their habitat, there is little evidence that they are compensating for the loss of populations on a broad scale

Effectiveness of translocation in mitigating reptile-development conflict in the UK

The translocation of reptiles from development sites is a frequent but controversial intervention to resolve reptile-development conflicts. A general lack of post-translocation monitoring means that the fate of translocated reptiles is largely unknown. Here we report on the outcome of six reptile translocations carried out to mitigate the impacts of development. Through detailed post-translocation monitoring, we sought to determine whether translocated reptiles established populations within the receptor sites. To determine the effect of translocation, we investigated six sites within the UK that had received populations of translocated slow-worm Anguis fragilis, viviparous lizard Zootoca vivipara, adder Vipera berus and / or grass snake Natrix helvetica. Identification photographs were taken of all reptiles during the translocation. Following release, between one and three years of post-translocation monitoring was undertaken; during the monitoring, identification photographs were again collected to establish whether captured individuals were part of the translocated populations. Very few translocated individuals were encountered during the post-translocation monitoring. The mean number of translocated reptiles was 98 (SE 19.61). Of these, an average of 1.5 (SE 0.72) individuals or 1.6% of the population were captured during the monitoring. No recaptures of translocated reptiles were made at three (50%) of the study sites. The low recapture rates of translocated reptiles could be due to mortality, imperfect detection (including inaccurate identification of individuals) or post-translocation dispersal. There is some limited evidence to support each of the possible options, but post-translocation dispersal is considered to be the most likely explanation. The study found no confirmatory evidence that mitigation-driven translocations are compensating for the losses of populations to development

Ranging behaviour of adders (Vipera berus) translocated from a development site

Translocation of animals from sites scheduled for development is a widespread but controversial intervention to resolve human-wildlife conflicts. Indeed, reptiles are very frequently the subject of such translocations, but there is a paucity of information on the fate of such animals or how their behaviour compares to residents. In 2014, a population of adders (Vipera berus) was translocated from a development site in Essex, UK. A sample of snakes was fitted with external radio tags and tracked for a period of 10 days during the spring. This exercise was repeated during the summer using a combination of translocated and resident individuals. Translocated males exhibited significantly greater average daily movements than resident conspecifics. Furthermore, all translocated males undertook long-distance, unidirectional movements away from the release site. In contrast, all translocated females remained within 50 m of the point of release. One of the males returned to the donor site, crossing large areas of unsuitable habitat in doing so. Translocated males also maintained significantly larger total ranges than resident conspecifics. No differences in range sizes were observed between translocated and resident females. The dispersal of male snakes from the release site may increase the risk of mortality of translocated snakes and reduces the likelihood of establishing a new population. Interventions to encourage the establishment of new home ranges within the boundaries of release sites may include mechanisms to prevent dispersal immediately following release