Rattlesnakes Show Population-Dependent Stress Responses

In an experiment with 28 adult Southern Pacific rattlesnakes, snakes from a population that overwinters individually displayed longer periods of stress-related cardiac acceleration and longer bouts of rattling than snakes from a population that overwinters communally. The study found no evidence that the presence of another snake reduced either cardiac or behavioral responses to an acute stressor, suggesting that social buffering in rattlesnakes may depend on the circumstances and methods used to detect it.

Researchers tested the snakes in an open-field arena under three conditions: alone, with a familiar companion, or with an unfamiliar companion. The animals came from lowland and montane populations of Crotalus oreganus helleri, populations that differ in their overwintering behavior. Lowland snakes overwinter individually, whereas montane snakes gather communally. The experiment examined whether population, sex, and companion familiarity influenced heart-rate responses, recovery, defensive posturing, and rattling during an acute stressful event.

The clearest population difference concerned the duration of the physiological and behavioral response. Although the magnitude of emotional tachycardia was similar between the populations, lowland snakes that overwinter individually experienced emotional tachycardia and rattled for longer than montane snakes that overwinter communally. This distinction is important because a stronger peak response is not necessarily equivalent to a more prolonged response. The researchers also found differences associated with sex: montane males clustered more closely together than females and were the least likely to rattle, although males and females showed similar cardiac responses.

Companion familiarity did not produce the expected pattern of stronger calming among familiar pairs. In fact, snakes placed with unfamiliar same-sex companions recovered from the cardiac response more quickly than those placed with familiar companions. Neither familiar nor unfamiliar companionship reduced cardiac responses or rattling relative to testing alone. These results provide no evidence of social buffering, the attenuation of a stress response through social contact. The finding contrasts with earlier reports of social buffering in rattlesnakes and points to the possible importance of experimental context in determining whether the phenomenon can be detected.

One possible complication is emotional contagion, in which an animal’s state reflects or matches that of a companion. If both snakes respond similarly to the stressor, a companion could obscure rather than reveal a buffering effect, because responses measured in a pair might be difficult to distinguish from mutual arousal. The authors therefore argue that future studies should explicitly test the conditions under which social buffering becomes detectable. The present experiment involved a specific open-field protocol, a modest sample of 28 adults, two populations distinguished by overwintering behavior, and controlled categories of companion familiarity. Its results show that social context did not consistently calm these rattlesnakes under those conditions; they do not establish that buffering is absent in every population, sex, life stage, or stressful situation.

Subject of Research: Acute stress responses in Southern Pacific rattlesnakes vary with population, sex, and social context.

Article Title: Cardiac and behavioral responses to an acute stressor in Southern Pacific rattlesnakes (Crotalus oreganus helleri): effects of population, sex, and companion familiarity

Article References: Martin, C. E., Streit, M. B., & Hayes, W. K. (2026). Cardiac and behavioral responses to an acute stressor in Southern Pacific rattlesnakes (Crotalus oreganus helleri): effects of population, sex, and companion familiarity. Frontiers in Ethology, 5, 1890331. https://doi.org/10.3389/fetho.2026.1890331

Image Credits: AI Generated

DOI: 10.3389/fetho.2026.1890331

Keywords: Southern Pacific rattlesnake, acute stress, social buffering, emotional tachycardia, defensive rattling, companion familiarity, population differences, overwintering behavior, reptile behavior, stress physiology, Cardiac, behavioral