Quantitative honesty in snakes: acoustic warning is influenced by sex, personality and correlates with bite risk in the nose-horned viper
Résumé
Aposematism has evolved as a strategy to warn predators of potential danger. While visual signals have received considerable attention, acoustic signals remain less studied despite their flexibility across contexts and individuals. We investigated defensive behaviours (hissing and biting) in the nose-horned viper (Vipera ammodytes). First, we assessed the repeatability of defensive behaviours under standardized conditions. Second, we quantified responses in a test arena simulating increasing threat levels: (i) no stimulation, (ii) visual stimulation, and (iii) combined visual and tactile stimulation. Hissing and biting were highly repeatable within individuals but varied markedly among them. Males showed a higher likelihood of exhibiting defensive behaviours than females. In the test arena, hissing and its acoustic variables (duration, intensity) increased with threat level. Biting occurred only during the visual and combined stimulation phases, and its frequency increased between the two periods. Consistent with the hypothesis of quantitative signal honesty, we found that hissing characteristics (number of hisses and hiss intensity) were positively correlated with the number of bites. Overall, our results reveal that defensive behaviour expression is influenced by personality traits, sex and threat level, highlighting the complexity of acoustic warning signals in snakes and their potential role as honest indicators of defensive capacity.
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