Significance of the dorsal zigzag pattern of Vipera latastei gaditana against avian predators

1. Aposematism is an antipredatory strategy in which prey animals conspicuously signal their noxiousness to potential predators. This successful strategy is based on avoidance learning of predators. 2. Most species in the viperid genus Vipera have a characteristic dorsal zigzag pattern. It has previously been suggested that the dorsal zigzag pattern of Vipera berus (the adder) has a cryptic function and thus makes the snake less conspicuous to avian predators. However, a recent experiment suggested that the pattern may function as an aposematic signal rather than being cryptic, and therefore induces active avoidance in avian predators. 3. We conducted a field experiment in Donana national park in Spain, testing whether the zigzag pattern gives survival value to Vipera latastei gaditana against avian predators. We used two sizes of plasticine models with a zigzag pattern vs. without a zigzag pattern to record attacks by avian predators. The background was controlled (white vs. natural) to exclude the possibility that one morph would be more cryptic to predators than the other one. We also tested size-dependent mortality against the signalling and nonsignalling snakes as aposematic signal is expected to enhance the survival of the aposematic species in a size-dependent manner. 4. Predation pressure against snakes was severe, and on average 39% of models were attacked. Coloration did not enhance the survival of juvenile-sized zigzag-patterned snakes, but significantly increased the survival of adult-sized zigzag-patterned snakes on both backgrounds. 5. Our results provide further support for the aposematism hypothesis of zigzag-patterned noxious snakes, although the advantage due to disruptive coloration is not mutually exclusive.