Tongue flicking heralds flight behaviour following passive antipredator displays in dice snakes

When captured, many prey respond by biting the predator or struggling to get free. However, one indirect escape option is death feigning (DF), in which complete immobility supposedly “tricks” the predator into abandoning its meal. But lying motionless and exposed to a predator is dangerous; therefore, individuals should optimize DF occurrence and duration. We captured colour polymorphic dice snakes (Natrix tessellata, Natricidae) (N = 271) in the field and measured two behavioural responses: (1) the occurrence and duration of immobility/DF; (2) the number of tongue-flicking sequences (TF). Tongue flicking is an essential component of a key sensory mechanism to check the safety of the environment before attempting escape. We experimentally assessed the relationship between these two behaviours and the effects of phenotypic characteristic of snakes on the occurrence and duration of immobility and of TF. Snake phenotype had multiple effects. Gravid females avoided DF and displayed more TF sequences during the tests compared to non-gravid females and males. Blotched snakes stayed immobile longer than green and melanistic snakes. Larger individuals remained in DF for longer and showed fewer TF sequences than smaller individuals. Snakes burdened with a recent meal postponed fleeing and displayed more TF sequences than snakes without food. Finally, snakes showing more TF sequences postponed fleeing, which suggests that dice snakes assessed predatory risks and adapted escape behaviour to their risk status. Future studies should examine how individuals estimate the appropriate timing to shift from immobility to escape.