Unusual change in activity pattern at cool temperature in a reptile (Sphenodon punctatus)

• We looked at the effect of temperature on behaviour of tuatara (S. punctatus).
• We compared their responses with a nocturnal gecko and a diurnal skink species.
• Similar to the diurnal skinks, tuatara emerged quickly at 20 °C and 12 °C.
• Like nocturnal geckos, tuatara were still active at 5 °C, but only during the day.
• Tuatara were diurno-nocturnal at 20 °C and 12 °C but strictly diurnal at 5 °C.

Animals that can be active both during day and night offer unique opportunities to identify factors that influence activity pattern. By experimental manipulations of temperatures under constant photoperiod, we aimed to determine if emergence, activity and thermoregulatory behaviour of juvenile tuatara (Sphenodon punctatus) varied at different temperatures (20 °C, 12 °C and 5 °C). To help clarify its activity pattern, we compared tuatara with two lizard species endemic of the South Island of New Zealand for which activity pattern is known and clearly defined: the nocturnal common gecko Woodworthia “Otago/Southland” and the diurnal McCann׳s skink Oligosoma maccanni. Tuatara showed similar responses to both species of lizards. Similar to the diurnal skinks, tuatara emerged quickly at 20 °C and 12 °C while nocturnal geckos took more time to emerge. Like nocturnal geckos, tuatara continued to be active at 5 °C, but only during the day. Interestingly, tuatara shifted from diurno-nocturnal activity at 20 °C and 12 °C to being strictly diurnal at 5 °C. We suggest that this temperature-dependent strategy maximises their survival during cold periods.