Position Within the Burrow and Behavioral Thermoregulation Jointly Shape Thermal Lability in a Fossorial Ectotherm.

Burrowing is a widespread thermoregulatory strategy among ectotherms, yet the spatial and temporal scales by which burrows buffer organisms from thermal extremes remain poorly quantified. We combined high-resolution temperature measurements from gopher tortoise (Gopherus polyphemus) burrows during an anomalous winter cold front and a prescribed fire with multi-year carapacial temperature data from free-ranging tortoises to characterize how belowground refuges mediate exposure to extreme cold and heat. Using Bayesian generalized additive models, we reconstructed continuous temperature fields within burrows and quantified how thermal variability attenuates with distance from the burrow entrance, measured along the burrow axis. During the cold front, thermal fluctuations declined gradually along the burrow, with a half-attenuation distance (distance at which thermal variability is reduced by 50% compared to values outside the burrow) of ~174 cm and an e-folding distance (distance at which thermal variability is reduced to ~37% of values outside the burrow) of ~251 cm, indicating that sustained cold forcing penetrated far into the burrow. In contrast, fire-associated heating attenuated rapidly, with half-attenuation and e-folding distances occurring at ~69 cm and 100 cm, respectively, indicating most thermal stabilization was achieved within the first meter of the burrow. Multi-year carapacial temperature data revealed strong seasonal structure not only in mean temperatures but also in daily thermal amplitude and the rate of temperature change, suggesting that tortoises regulate both thermal exposure and thermal lability through behavioral use of burrows. Together, these results demonstrate that burrows act as dynamic thermal filters whose buffering capacity depends on position within the burrow and on the type and duration of the disturbance, providing quantitative insight into how animal-engineered refugia shape ectotherm thermal ecology in environments characterized by increasing climatic and disturbance variability.