Will climatic changes affect the Vietnamese crocodile lizard? Seasonal variation in microclimate and activity pattern of Shinisaurus crocodilurus vietnamensis

Climate change is considered to negatively affect vertebrate biodiversity. Lizards in tropical regions are considered particularly vulnerable due to their narrow temperature tolerances. The crocodile lizard Shinisaurus crocodilurus, an ecologically specialized semiaquatic species, is under the risk of extinction due to habitat loss and overharvesting. It is only found in isolated relict populations in southern China and northern Vietnam. Data on the thermal niche of the species are crucial to assess its vulnerability to climatic changes. We developed a backpack system with temperature data loggers for S. crocodilurus in order to monitor the lizard’s temperature preferences in its natural habitat in Vietnam. We found that S. crocodilurus vietnamensis preferred a mean ambient temperature range of 24 ± 1°C (min-max: 22-31°C) at natural habitat sites, a far lower temperature amplitude compared to the recorded ambient temperature range at habitat sites. In its natural habitat, S. crocodilurus vietnamensis avoided in particular high temperatures, indicating the importance of constantly cool streams and intact vegetation for the provision of shade and shelter. We further provide first insights into the seasonal variation in microhabitat use and activity of S. crocodilurus vietnamensis based on data from individuals kept in outdoor enclosures under natural climatic conditions in Vietnam, collected daily over a period of eight months. Our results aim to aid further conservation measures for the species, such as the identification and protection of core habitat sites and sites for restocking, as well as to adjust and improve conservation breeding programs for the species.