The Impact of Death Feigning Behaviour on the Survival of Grass Snake (Natrix natrix): A Study with Plasticine Models

Death feigning (thanatosis) is the antipredator behaviour of grass snake (Natrix natrix) which can contribute to its survival. Since this is difficult to study under natural conditions, in our experiment we used four types of plasticine models of grass snake to mimic its different behaviour types. The advantage of using plasticine models is that they preserve the traces of the predators. The study was conducted at two different locations in Kis-Balaton, one of the largest wetlands in the Carpathian Basin. Only 8.75% (n = 21) of all grass snake models (n = 240) were damaged by predators. The predation activity of birds (76%) was significantly higher than that of mammals (24%), the latter left imprints only on models imitating live (uncoiled, coiled) grass snakes. Among predated models, 62% showed injuries on the midbody, 24% on the tail tip, and 14% on the head. Predation rates were similar in spring and autumn periods, and on the abandoned railway and road. Comparisons of daily survival rates between different model types suggested that the coiled (basking and death feigning) pose may provide an advantage in survival. In some cases, the visible colour pattern of the models may have affected their detectability. The higher survival rates of the grass snake models imitating death feigning indicate the adaptive value of this antipredator behaviour.