Thermal biology characteristics of the Caspian whipsnake (Dolichophis caspius, Gmelin, 1789) under natural and laboratory conditions.

Reptiles rely on behavioural thermoregulation to maintain optimal body temperature (Tb), essential for many physiological functions. However, thermal biology remains poorly studied in many snake species, including the Caspian whipsnake (Dolichophis caspius, Gmelin, 1789). This study examined the thermal biology of the Caspian whipsnake under natural and laboratory conditions. In the field, we investigated the influence of sex, age category, season, time of day, air temperature, detection status, feeding status, and shedding phase on Tb. Under controlled conditions, we assessed preferred Tb variation and its relationship to active thermoregulation. In the field, Tb was significantly affected by sex, season, time of day, air temperature, feeding status, and shedding phase, but not age category, body size or detection status. Males had lower Tb than females and snakes with food in their stomachs exhibited higher Tb. Tb increased from March to June and from morning to afternoon, and air temperature had a positive effect on Tb. In the laboratory, mean Tb (24.5 ± 4.9 °C) was lower than in the field (26.9 ± 5.2 °C) and was significantly associated with body posture and terrarium part, indicating active behavioural thermoregulation. In the laboratory, males had lower Tb than females, and juveniles had lower Tb than adults. The lower thermal preference suggests a cooler thermal niche than many colubrids, potentially increasing their susceptibility to climate warming. However, the broad Tb variation and behavioural thermoregulation indicate some flexibility in responding to environmental changes. These findings highlight the role of behavioural thermoregulation in snake thermal responses to environmental variation.