Reptiles: Tuatara

Range: New Zealand Habitat: islands, scrubland

What makes them
so different?

The tuatara is one of the most unique animals in the world. Although it looks like a lizard, it really is quite different. The tuatara’s closest relatives are an extinct group of reptiles that were around at the time of the dinosaurs. This is why some scientists refer to tuataras as “living fossils.”

Both male and female tuataras have a crest of spiky scales, called spines, down the center of their backs and tails. The name “tuatara” is a native Maori word meaning “peaks on back.” Tuataras have no external ears as lizards do. They enjoy cooler weather, while lizards like it warm. And, unlike lizards, tuataras are nocturnal. But their most curious body part is a “third eye” on the top of the head. The “eye” has a retina, lens, and nerve endings, yet it is not used for seeing. It is visible under young tuataras’ skin but becomes covered with scales and pigment in a few months, making it hard to see. The unique eye is sensitive to light and may help the tuatara judge the time of day or season.

Taking it slow

Tuataras grow very slowly and don’t stop growing until they are about 30 years old. They don’t reach maturity until they are 13 to 20 years old. It is believed that this remarkable reptile can live 80 years in the wild! They have a slow metabolism and can go for an hour without breathing if they need to. The islands they live on can get cold, and tuataras can stay active in cold weather, unlike other reptiles.

A burrow is best!

Whenever a tuatara senses danger, it scurries to the nearest burrow it can find. Tuataras don’t care if the burrow belongs to someone else, like a nesting seabird! Often they will share a burrow with the birds. The bird goes off fishing during the day, and the tuatara goes out feeding at night. Sounds like a good arrangement, doesn’t it?

What’s on the menu?

Adult tuataras are active at night because that’s when their food is most available. They eat mostly insects, especially beetles, but have been known to eat lizards, birds, and bird eggs. Young tuataras usually hunt for food during the day to keep from being eaten by adult tuataras at night! There are two rows of teeth on the tuatara’s upper jaw and one row on the lower jaw that fits between the upper rows of teeth when the mouth is closed. The arrangement of the teeth helps tuataras tear apart hard insects. These small teeth are not replaced when lost or broken, and older tuataras have to eat softer food items as their teeth wear down. The tuataras at the San Diego Zoo are fed earthworms and crickets.

Boy or girl?

In the wild, tuataras breed in March, and females lay soft-shelled eggs in nesting burrows eight months later. The eggs incubate for 13 to 16 months before hatching. Sadly, this extremely long time gives predators, usually rats, plenty of opportunities to have tuatara eggs for breakfast, lunch, or dinner! Tuatara hatchlings are on their own as soon as they break out of their eggs, as the mother does not stay to protect the eggs or her babies. The hatchlings are more active than the adults and must quickly find food and dig small burrows for protection.

Like some other reptiles, such as alligators, the temperature of the nest where it incubated as an egg determines a tuatara’s gender. It has been found that a difference of just one degree centigrade can change the young in a clutch of eggs from all females to all males! Since higher temperatures create more males, there is some concern about the effects global warming could have on the survival of tuatara populations.

An amazing discovery

In 1989, a group of tuataras was discovered on Brothers Island, a tiny, 10-acre (4-hectare) “rock” island. About 600 tuataras live here on a 5-acre (2.2-hectare) patch of scrub vegetation at the top of the island. This “new” species was given the name Brothers Island tuatara Sphenodon guntheri in 1990.

Tuataras in trouble

Tuataras used to inhabit the two major islands in New Zealand and numbered in the millions. Then, the first humans arrived from Polynesia, bringing rats and dogs that ate tuatara eggs and youngsters. When Europeans arrived in New Zealand they also brought more dogs and rats, as well as cats and ferrets. These “introduced” animals wiped out most populations of tuataras. The threat to tuataras was so serious that in 1895 the New Zealand government fully protected tuataras and their eggs. Even with this protection, tuatara populations continued to disappear as rats reached one island after another. The most recent extinction of an island population happened in 1984, when rats killed all the tuataras on a 25-acre (10-hectare) island in just 6 months. Recent studies have confirmed that tuatara populations on islands without rats are much larger than populations on islands with rats. Today tuataras survive on just 30 tiny offshore islands in New Zealand.

From dark days to a brighter future

The New Zealand Department of Conservation launched a recovery program for the tuatara in 1988. The program aims to stop the continuing extinction and help tuataras threatened by rats. Hatchlings are raised by biologists until large enough to survive in the wild, a process called “headstarting.” They are then released on rat-free islands. This new hope for tuataras is good news for other species, too. Restoring natural habitat for tuataras also helps other animal species like the kiwi, several seabirds and lizards, and a large flightless insect called a giant weta. These animals had also been harmed by the rats and other introduced predators. The San Diego Zoo is one of two zoos selected to hold a satellite colony of the Brothers Island tuatara. They are currently in an off-exhibit area. With these programs in place, tuataras and other animals native to New Zealand have a brighter future ahead.