The physiology of an animal determines the range of environmental conditions under which it can survive. Surprisingly, relatively few conservation studies have used physiology to make predictions about the performances of translocated individuals in their new environment. Tuatara Sphenodon punctatus are of international significance as the last rhynchocephalian reptile. Natural populations are now restricted to ∼30 offshore islands in northern New Zealand, where survival of at least one population is threatened by climate change. Translocation to cooler regions (further south, but within the past latitudinal range of the genus) is an important option for future management. However, the genetic suitability of available source populations for environments that are currently cooler is unclear. To help predict the success of translocation, we examined the effects of cool temperature on juveniles sourced from one of the most southerly natural populations and compared these with three lizard species that inhabit southern New Zealand. We found that tuatara possess the same range of preferred body temperature, feeding responses to cool temperatures and critical thermal minimum as these three lizard species. However, tuatara did not digest at temperatures below 12 °C, suggesting that new reintroduction sites must offer enough basking opportunities to allow digestion of prey in winter. As tuatara showed responses to cold temperatures similar to lizards from southern New Zealand, we predict that tuatara will survive if translocated south of their current range, but whether they will be able to produce self-sustaining populations still needs investigation. Physiological predictions from the current study should now be combined with measurements of population performance in an experimental translocation.