Rare reptiles known as tuatara (the last two species of the order Sphenodontia) survived the age of the dinosaurs, but the age of man has given them a bit more trouble. After living in New Zealand for millions of years, tuatara were completely wiped out on the country's two main islands by invasive Polynesian rats (also known as kiore, Rattus exulans Peale) even before the arrival of European settlers (who brought their own rat species, the Norway rat, Rattus norvegicus). Today they only exist in sanctuaries and on three dozen smaller islands off the New Zealand coast.

Now tuatara have one more habitat to help ensure their long-term survival. On March 25, 60 tuatara were released on Motuihe Island, located a ferry's ride away from the city of Auckland. The New Zealand Department of Conservation (DOC) and the Motuihe Trust spent many years ridding the island of non-native predators and other pests, making it a safe haven for many threatened species unique to New Zealand.

"DOC eradicated Norway rats and mice from Motuihe in 1997," DOC Auckland Area Manager Brett Butland said in a prepared release. "We made the island completely pest-free by removing feral cats and rabbits in 2005. Removing the pests, particularly rabbits, enabled the Motuihe Trust to establish a nursery on the island that produces up to 55,000 native plants a year." The growth of native plants has enhanced the island's suitability as a habitat for New Zealand native species, and the tuatara now join other endangered or threatened species that have been released on the island, including the little spotted kiwi (Apteryx owenii), kakariki (parakeets of the genus Cyanoramphus), tieke (Philesturnus carunculatus), bellbird (Anthornis melanura) and shore skink (Leiolopisma smithi).

The 60 tuatara moved to Motuihe came from another DOC-managed isle, Lady Alice Island, which was cleared of all rat species in the 1990s. The relocated tuatara represent less than 1 percent of the reptiles from the Lady Alice population, according to the DOC.

The public will be able to visit Motuihe to see the tuatara in the wild, but keeping the island predator-free will remain vital to their survival there. "We need everyone traveling to Motuihe, and other pest-free islands in the Hauraki Gulf Marine Park, to check their boat, kayak and gear to ensure they're not carrying stowaway pests," Butland said.

Half of the 60 tuatara were released during a public event, which included a special "handing over ceremony" from the Ngātiwai Maori iwi (society) representing the Northland region of New Zealand, which includes Lady Alice Island. (Stuff.co.nz has footage of the ceremony and the first tuatara release here.) The rest of the reptiles were released after the public had left to ensure the new residents' safety.

Tuatara are not currently endangered, due to years of intense conservation efforts, although they remain at risk. Eight of the islands they inhabit still contain Polynesian rats, which prey on eggs and the youngest reptiles, affecting their populations' ability to grow. The reptiles are also valued in the European illegal pet trade, where a single tuatara can fetch more than $40,000 on the black market.

Meanwhile, scientists fear that climate change could further threaten the two species. Like many reptile species, the gender of tuatara hatchlings is determined by the temperature of their eggs in the nest. Unlike most reptiles, which produce more females when nests are warmer, tuatara eggs tend to hatch more males when temperatures rise. Tuatara populations already skew slightly more male than female.

The relocation cost of about $33,000 was raised by the Motuihe Trust. The DOC and the Trust hope these 60 tuatara will eventually grow to a population of 18,000—although they say that could take about 300 years.

Tuatara are medium-size reptiles, about half a meter in length and weighing up to one kilogram. They mature slowly, reaching sexual maturity at about age 23, and breed only once every nine years, but have been known to live to be more than 100 years old. The two species are the only survivors of the order Sphenodontia, which dates back more than 200 million years.

Photo: A Cook Strait tuatara (Sphenodon punctatus) by Sid Mosdell via Flickr. Used under Creative Commons license