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IUCN threat status:

Vulnerable (VU)

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Biology

The Brothers Island tuatara is terrestrial and primarily nocturnal, though, as an ectotherm, it spends part of its day basking in the sun outside its burrow to warm up. It does not drink water, and feeds at night on insects, worms, snails, birds eggs, chicks and occasionally even its own young (4). A special type of jaw movement allows the tuatara to shear bony prey with ease (5). In addition, the tuatara has pronounced jaw muscles due to the skull's bone arrangement: like most modern reptiles (except for turtles), this species has a diapsid skull. This means it has two holes behind the eye-holes, and a greater bone surface area for muscle attachment. As a result the tuatara's head is huge, the jaw muscles pronounced, and the bite ferocious (6). They often take over and live in bird burrows, though tuatara can and frequently do construct their own burrows (5). Several may use the same burrow, although at different times, and residents can be quite aggressive to intruders (5). Females only reproduce once every two to five years, and males compete for the right to mate, with territorial displays, aggressive fights and erected crests to make them appear larger than they are (4). Mating occurs between January and March and eggs are laid from October to December (2). About 8 to 15 eggs are deposited in small, specially constructed chambers, covered with soil and abandoned. They hatch after 12 to 15 months, which is the longest hatching time for any reptile (2) (5). The sex of the offspring is determined by the temperature: warm soil temperatures produce males, while cool soil temperatures produce females (5). Individuals reach maturity between 9 and 13 years of age, which may seem late, but these fascinating reptiles are believed to live for over 100 years (2). Their long life is the product of having an extremely low metabolic rate, and a slow growth rate, which is due to their tolerance to extremely cool weather. Indeed the activity levels of the tuatara peak at body temperatures of 12 to 17 degrees Celsius, the lowest for any reptile. This is probably why they have been able to survive in New Zealand's temperate climate for so long (4).

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