Detectability of Elusive Reptiles under Artificial Cover Objects is Species- and Year-Specific

ABSTRACT Field surveys of rare and elusive reptiles often encounter the problem of low detectability. Therefore, several techniques have been invented to improve detection probability and artificial cover objects (ACOs) are among the most commonly used in reptile studies. However, the methodological effectiveness of ACOs has been rarely evaluated and focused mostly on spatial aspects. The temporal dimension of the ACOs effectiveness remains still understudied, despite well-known seasonal variation in reptile activity patterns. Here, we examined seasonal and between-year variation in the fraction of occupied ACOs, as a proxy for detectability, in two elusive reptile species, the slow worm Anguis fragilis and smooth snake Coronella austriaca. We found that the use of ACOs was species-specific and showed high temporal variation. In the case of smooth snakes, monthly usage varied between years; specifically within-year variation of the proportion in occupied ACOs was most pronounced in 2015, but seems vanishing in consecutive years. This loss of of seasonal pattern occurs only in the last year of survey in the case of slow worm and monthly use of ACOs seem not to vary between years. Considerably low detectability of the studied species by the ACO method in some years may not necessarily indicate their low population density, but rather results from shifts in their diurnal activity and/or microhabitat use dependent on ambient temperatures. Increasing between-year variation in weather conditions may reduce repeatability of seasonal patterns of ACO usage, making we suggest additional detection techniques that could bee incorporated.