Threat level and sound production mode modulate acoustic warnings and defensive biting in snakes
Abstract
Accurately assessing predation risk is important because it enables prey to match their defensive behaviours to the level of threat and avoid unnecessary investment in costly responses. According to the threat sensitivity hypothesis, prey should optimize the trade-off between the costs of active defence and mortality risk by escalating their responses as danger increases. Yet, the transition from warning signals to physical confrontation remains largely understudied, particularly in relation to different acoustic signalling modes. We studied 220 individuals from 73 snake species representing four modes of acoustic warning production: two simple modes (hissing and tail vibration) and two highly specialized modes (rattling and scale rubbing). Individuals were exposed to three phases of escalating threat: a low-threat phase without directed predator-like stimulation, a medium-threat phase involving visual stimulation and a high-threat phase combining visual and tactile stimulation. Accounting for phylogeny, our findings supported the threat sensitivity hypothesis: both acoustic signalling investment and biting increased with perceived risk. Warning signals became longer and generally more intense as threat increased, while biting occurred primarily at the highest threat level. However, escalation patterns differed among sound production modes. Rattling and scale rubbing showed steeper increases in signal duration with threat than hissing, while tail vibration showed an intermediate pattern. Sound intensity also varied among modes: hissing increased throughout the escalation sequence, rattling increased overall but plateaued between the medium-and high-threat phases, scale rubbing increased during the initial escalation before plateauing and tail vibration showed no significant modulation. Body mass also predicted physical defence, with larger individuals being less likely to engage in confrontation. Our results demonstrate that defensive responses in snakes are dynamic sequences in which acoustic warnings escalate with perceived risk and biting serves as a last-resort tactic. They further show that the way acoustic signals escalate is shaped by their mode of production, highlighting the importance of considering signal- production mechanisms when investigating threat-sensitive defensive behaviour.
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BibTeX
@article{zele2026threat,
title = {{Threat level and sound production mode modulate acoustic warnings and defensive biting in snakes}},
author = {Nicolas van Zele and Simon Baeckens and Matéo Millet and Elsa Daniaud and Rémi Ksas and Marc Jaeger and Olivier Calvez and Thierry Lengagne and Olivier Lourdais},
journal = {Functional Ecology},
year = {2026},
month = oct,
doi = {10.1111/1365-2435.70452},
url = {https://hal.science/hal-05788098v1},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Threat level and sound production mode modulate acoustic warnings and defensive biting in snakes
AU - Nicolas van Zele
AU - Simon Baeckens
AU - Matéo Millet
AU - Elsa Daniaud
AU - Rémi Ksas
AU - Marc Jaeger
AU - Olivier Calvez
AU - Thierry Lengagne
AU - Olivier Lourdais
PY - 2026
DA - 2026/10/06
JO - Functional Ecology
DO - 10.1111/1365-2435.70452
UR - https://hal.science/hal-05788098v1
AB - Accurately assessing predation risk is important because it enables prey to match their defensive behaviours to the level of threat and avoid unnecessary investment in costly responses. According to the threat sensitivity hypothesis, prey should optimize the trade-off between the costs of active defence and mortality risk by escalating their responses as danger increases. Yet, the transition from warning signals to physical confrontation remains largely understudied, particularly in relation to different acoustic signalling modes. We studied 220 individuals from 73 snake species representing four modes of acoustic warning production: two simple modes (hissing and tail vibration) and two highly specialized modes (rattling and scale rubbing). Individuals were exposed to three phases of escalating threat: a low-threat phase without directed predator-like stimulation, a medium-threat phase involving visual stimulation and a high-threat phase combining visual and tactile stimulation. Accounting for phylogeny, our findings supported the threat sensitivity hypothesis: both acoustic signalling investment and biting increased with perceived risk. Warning signals became longer and generally more intense as threat increased, while biting occurred primarily at the highest threat level. However, escalation patterns differed among sound production modes. Rattling and scale rubbing showed steeper increases in signal duration with threat than hissing, while tail vibration showed an intermediate pattern. Sound intensity also varied among modes: hissing increased throughout the escalation sequence, rattling increased overall but plateaued between the medium-and high-threat phases, scale rubbing increased during the initial escalation before plateauing and tail vibration showed no significant modulation. Body mass also predicted physical defence, with larger individuals being less likely to engage in confrontation. Our results demonstrate that defensive responses in snakes are dynamic sequences in which acoustic warnings escalate with perceived risk and biting serves as a last-resort tactic. They further show that the way acoustic signals escalate is shaped by their mode of production, highlighting the importance of considering signal- production mechanisms when investigating threat-sensitive defensive behaviour.
SN - 0269-8463
SN - 1365-2435
ER -