Tuatara Biology

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General Facts
Growth & Longevity
Sex & Reproduction

General Facts

Below are some general biological facts about tuatara.

• The colour of tuatara ranges from olive green to brown to orange-red
• Tuatara can croak when disturbed
• Adult tuatara are terrestrial and nocturnal, although they will often bask in the sun to warm their bodies
• Hatchling tuatara are more diurnal in their activity
• Tuatara can autotomise their tail
• Tuatara have the lowest metabolism of all reptiles
• Tuatara have the rarest form of temperature-dependent sex determination, Type 1b, where males are produced at 21°C and above
• Like all reptiles, tuatara are ectothermic, yet they are active at very low temperatures, maintaining normal activity at temperatures as low as 7°C. The optimal body temperature range is 16-21°C, the lowest of any reptile

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Growth & Longevity

Scientists measure tuatara from the tip of their snout to their cloaca. This measurement is known as the snout-vent length (SVL). The two species of tuatara differ in size.

Sphenodon guntheri : On Nga Whatu/North Brother Island female Sphenodon guntheri can reach 215 mm SVL and weigh up to 325 g, whereas males can grow up to 250 mm SVL and weigh up to 655 g. On islands where S. guntheri have been translocated their sizes are much larger, probably due to increased resources, reaching a SVL of 261 mm and mass of 735 g 11 years after release.

Sphenodon punctatus: On Takapourewa/ Stephens Island females can grow up to 255 mm SVL and weigh up to 505 g, and males can grow up to 300 mm SVL and weigh up to 995 g. Past records indicate that tuatara on Takapourewa /Stephens Island reached much larger sizes, with females weighing in at 610 g and males at 1020 g. Animals are probably smaller now because less food is available due to the large numbers of tuatara on the island.

Tuatara appear to have indeterminant growth. We don’t know how long tuatara can live, but estimate that it is over 100 years. The oldest wild tuatara recorded is an 88 year old female. It will take many more years of research to determine the longevity of tuatara.

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Sex & Reproduction

Sex: tuatara are sexually dimorphic. Adult males are larger than females, with a larger head, more prominent dorsal spines, a larger throat which can be inflated, and a narrower abdomen. Unlike other male reptiles, male tuatara do not have a penis and will inseminate the female by lifting her tail with his and placing his cloaca over hers, similar to many birds.

Courtship & Mating: Tuatara reach sexual maturity in their early teens. Males mate each year whereas females mate every 2 to 6 years (average 4 years). Tuatara mate in mid-summer (February-March). During courtship the male will raise his crest, and walk slowly around the female with stiffened legs. The female will then either mate with the male or move away, usually down a burrow.

Egg Development & Nesting: Tuatara eggs have tough, white leathery shells. It takes the females between one and three years to provide the eggs with yolk, and after copulation up to seven months to form the shell. In early spring following copulation the female will leave her home burrow and trek to the rookeries where females congregate to lay eggs. The female will then spend time digging a hole in the ground for her nest. Often she will dig up a pre-existing nest, tossing aside any eggs or hatchlings from that year or the year before. The female will lay between 1 and 19 eggs in the end of the nest and fill the hole with dirt and grass. Sometimes she will then guard her nest for 1 to 10 days before heading back to her home burrow.

Incubation & Hatching: The eggs are left in the ground to incubate, and will take between 11 and 16 months to hatch. During this time the eggs are exposed to other females digging the nest up and tossing them aside, desiccation, temperature extremes and predation by beetle larvae. The sex of the hatchlings is determined by the temperatures that the developing embryos are exposed to during the sex-determining stage. The pivotal temperature is around 21°C; below 21°C females are produced, above 21°C males are produced. If all goes well the juveniles will develop in the eggs, and hatch using their caruncle, digging their way to the surface.