- 1It is widely accepted that reptiles are able to regulate behaviourally their body temperature (Tb), but this generalization is primarily based on studies of lizards and snakes in the temperate zone. Because the precision of Tb regulation may vary considerably between taxa and over geographical ranges, studies of semi-terrestrial turtles in climatic extremes are relevant to the understanding of reptilian thermoregulation.
- 2We studied thermoregulation in 21 free-ranging wood turtles (Glyptemys insculpta) at the northern limit of their range in Québec, using miniature data loggers to measure their internal Tb and external temperature (Text) continuously. We simultaneously recorded the available operative environmental temperature (Te) using 23 physical models randomly moved within each habitat type, and we located turtles using radiotelemetry.
- 3The habitat used by wood turtles was thermally constraining and the target temperature (Tset) was only achievable by basking during a short 5-h time window on sunny days. Wood turtles did show thermoregulatory abilities, as determined by the difference between turtle Tb distribution and the null distribution of Te that resulted in Tb closer to Tset. Although most individuals regulated their Tb between 09.00 h and 16.00 h on sunny days, regulation was imprecise, as indicated by an index of thermoregulation precision (| Tb – Tset |).
- 4The comparison of habitat use to availability indicated selection of open habitats. The hourly mean shuttling index (| Text – Tb |) suggested that turtles used sun/shade shuttling from 09.00 to 16.00 h to elevate their Tb above mean Te.
- 5Based on laboratory respirometry data, turtles increased their metabolic rate by 20–26% over thermoconformity, and thus likely increased their energy gain which is assumed to be constrained by processing rate at climatic extremes.