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Can the ancient tuatara adapt to global warming? University graduate Jeanine Refsnider plans to find out.Photograph by Simon Wilson

By Hudson Sangree

The tuatara of New Zealand have an unusual problem with sex. It isn’t a new problem for the spiky green reptiles, but it could get a lot worse, with dire consequences.

The tuatara are the last remnants of an ancient order of reptiles known as the rhynchocephalians, or “beak heads,” that lived throughout much of the world 220 million years ago. About 18 inches long and resembling an iguana with bits of crocodile, salamander, and dinosaur thrown into the mix, today’s tuatara is nearly identical to 140-million-year-old tuatara fossils, making it among the oldest unchanged vertebrates on earth. Tuatara have lived through ice ages, killer meteors, massive volcanic eruptions, and the shifting of the continents. They saw their cousins the dinosaurs come and go. In the last 1,000 years, the arrival of humans and the predators they introduced wiped out the tuatara on mainland New Zealand. Now they survive as a protected species on offshore islands and are the focus of intensive conservation efforts.

That does not mean they are out of danger, however. After enduring across the eons, the tuatara could be facing another serious threat because of global warming, says Jeanine Refsnider (B.S. ’99 Morris, M.S. ’05), a 28-year-old University of Minnesota graduate who is studying the creatures in New Zealand with the aid of a prestigious Fulbright grant. Refsnider is trying to see how quickly the tuatara can adjust to rising temperatures in order to avoid extinction.

In her office at Victoria University in Wellington, she explains that the temperature in tuatara nests determines the gender of hatchlings. More than 22 degrees Celsius (71.6 degrees Fahrenheit), and all tuatara are born male. Less than 21 degrees (69.8 degrees Fahrenheit), and all are female. If the air stays warm for too many consecutive years, it could be a reproductive disaster for the tuatara, with only males being born, she says.

Clearly, the tuatara have found ways to cope with climate change before, perhaps simply by moving their rookeries or nests to warmer or cooler spots. But Refsnider contends that global warming is happening much more quickly than past temperature swings, and she worries that the tuatara could be too slow to move their nests. She cites the work of the United Nations Intergovernmental Panel on Climate Change, which estimates that global surface temperatures will rise from between 1.4 and 5.8 degrees Celsius (2.52 and 10.44 degrees Fahrenheit) by the end of this century.

“If before it’s taken 10,000 years to change a couple of degrees, and now it happens in 100 years, the question is how flexible are tuatara in looking for new places to nest?” Refsnider says. “Climate change in the past has happened slowly. This is happening so fast, they may not be able to adapt quickly enough.”

Refsnider grew up in Coon Rapids, Minnesota. She received her bachelor’s degree in biology and her master’s in conservation biology. She made her first mark in the world of reptile ecology as a graduate student, with a study of the breeding habits of Blanding’s turtles in Minnesota. When she returns to the United States next year, she plans to pursue a Ph.D. in ecology and evolution, specializing

Tuatara females lay about eight eggs, which incubate for a year. Photograph by Jeanine Refsnider

in reptiles.

Endangered species, and reptiles in particular, have long fascinated Refsnider. When she was 8 years old, she saved her allowance to buy a fox snake from a pet shop. As a high school and college student, she volunteered at Springbrook Nature Center in Fridley, Minnesota, and adopted abandoned snakes and other reptiles as pets. Her box turtle and 10-foot-long boa constrictor are living in her parents’ basement while she is in New Zealand.

Her father, Ron Refsnider (M.S. ’78), says his daughter showed her proclivity for unusual animals at an early age. She carried around a rubber shark instead of dolls, he says, and collected offbeat stuffed toys, including an aardvark and a spiny anteater.

Ron Refsnider works as an endangered species biologist for the U.S. Fish and Wildlife Service, and Jeanine Refsnider grew up helping her father with his field research. While in the sixth and seventh grades, she worked with him on a study of Kirtland’s warblers, a unique and endangered bird species in the Upper Midwest.

“Conservation biology is something that almost seems to be in her blood,” he says. “She started with me working with birds, and moving to tuatara is a natural step. Reptiles have always been her first love.”

“I’ve been learning about science from an early age and doing things in a scientific method,” she says. “I was really lucky I was able to do that. I’ve always been interested in learning enough about threatened species to be able to protect them.”

Altogether, Refsnider is spending a year and a half in New Zealand, working on her own and as part of a research team from Victoria University. Between stints in Wellington, she and her colleagues live among the tuatara on Stephens Island, a remote and rugged prominence off the northeast tip of New Zealand’s South Island. There are some 30,000 to 50,000 tuatara on Stephens Island, by far the largest concentration of the reptiles in the world. Much smaller groups, from a few dozen to a few hundred individuals, live on about 30 other offshore islands.

Stephens Island’s sheer cliffs and rough seas prevent boat landings, so the researchers arrive by helicopter. They make their home in a former lighthouse keeper’s residence and, other than two wildlife rangers, are the only humans on the island. Refsnider spent six weeks on Stephens Island last year and plans to return again for six weeks this year. Her visits coincide with the tuatara breeding season in the austral spring months of late October through early December.

She goes out every night, visiting tuatara rookeries and often working until morning. She marks females and keeps track of their movements and choice of nest sites. Tuatara have little fear of humans and can easily be

Tuatara eat insects, spiders, small lizards, and seabird eggs and chicks. Photograph by Jeanine Refsnider

caught and studied at night, she says.

Tuatara are long-lived creatures. According to Refsnider, the oldest known individual on Stephens Island is 80 years old, and scientists speculate that some may live to be 120. They are slow to mature and do not reproduce until they are about 20 years old. They are also slow to breed. Female tuatara nest every two or three years. They lay about eight eggs on average, which take a year to hatch. The females leave their forest burrows and always return to the same rookeries on rocky hillsides to make their nests. Whether the tuatara have the flexibility to change their nest sites within the rookeries to adjust for temperature is a key question of Refsnider’s study.

On Stephens Island, recent summer months have been among the warmest on record and things are definitely heating up for the tuatara, Refsnider says. To test whether the creatures would nest in cooler spots if they had the option, she designed a simple but first-of-its-kind experiment. Refsnider uses shade cloth to create cooler nesting sites within the rookeries and monitors the females to see whether they opt for the shade. “We’re actually giving the animals a choice to see what they do under different conditions,” she says. “If they try to compensate for global warming, you would expect more of them to nest under the shade cloth.”

The results aren’t in yet, but Refsnider says she hopes to have enough data after her next trip to Stephens Island to predict whether the tuatara might change their nesting behavior in response to increasing temperatures.

Refsnider’s experiment follows up on a prior study done by Victoria University researchers that determined the exact temperatures at which tuatara become male or female in the egg. Nicky Nelson, the graduate student who led that study, is now a biology professor at Victoria and Refsnider’s supervisor. Nelson says that Refsnider’s project could be vital to helping the tuatara survive during the next century of global warming. 

“The climate change we’re seeing is pretty extreme,” Nelson says. “The females must modify their behavior so the sex ratio doesn’t get too skewed toward males. It’s not something they can respond to genetically over centuries. That’s not an option. They have to respond within their lifetimes.”

Currently, an experiment is under way to reintroduce tuatara on the mainland, in a fenced and predator-free area of the Karori Wildlife Sanctuary in Wellington. If all goes well there, more releases could happen in the next few years. Refsnider says her experiment could have a lasting practical application in such efforts.

“We can put them anywhere, but if there’s no place to nest they will just die out eventually,” she says. “Obviously we need to make sure their habitat, including nesting sites, is suitable. We’re still not sure what they like—what makes a good nest spot for them. They go to the same spot every year but what, exactly, makes that spot attractive to them is still a question.”

Tuatara is a Maori name that means “peaks on the back,” referring to the reptiles’ spiky crests. Tuatara originated during the Mesozoic era, when the rhynchocephalians lived throughout Asia, Europe, Africa, and North and South America.

A tuatara yearling. Adult tuatara grow to be about 18 inches long. The oldest known tuatara on Stephens Island is 80 years old, and scientists speculate that some tuatara might live to be 120. Photograph by Jeanine Refsnider

Only the tuatara of New Zealand avoided extinction because New Zealand separated from the super continent of Gondwanaland about 85 million years ago, before mammals evolved as predators. Today, tuatara are the sole occupants of their own order in the reptile class. The other three orders include crocodiles and alligators, snakes and lizards, and turtles.

The relatively recent arrival of humans ended the tuatara’s protective isolation and decimated their population on the mainland. By most estimates, the Maori came to New Zealand from Polynesia between 700 and 1200 A.D. European settlers arrived in greater numbers during the 1800s. Both groups cleared and burned the native forests, introduced predators, and hunted many unique species to extinction or near-extinction.

The tuatara suffered from habitat destruction, as the forests where they burrowed were cleared for farming and sheep pasture. Introduced predators, such as the Polynesian rat and the English stoat, an ermine, competed with the tuatara for food—mainly insects and spiders, small lizards, and seabird eggs and chicks. As adults, tuatara have no serious predators, but introduced mammals eat their eggs and young.

Reintroducing the tuatara and keeping the species going are top priorities for the Kiwis, who have undertaken intensive conservation efforts after seeing much of their native flora and fauna wiped out by the impact of humans on New Zealand’s fragile ecosystems.

Saving the tuatara is important not just for its own sake, but because it is a vital part of its natural environment, Refsnider insists. On Stephens Island, for example, the burrowing creatures mix seabird droppings with the soil, making it more fertile in exposed, rocky areas. In the forest, their digging uproots seedlings, creating a mature forest with little understory, maintaining its and other creatures’ habitat.

Professor Nelson says tuatara are also important as a window into the world of reptiles that predated the dinosaurs. “As representatives of this ancient group of reptiles they provide a link to the past,” she says. “They are called ‘living fossils,’ which isn’t really accurate, but it shows their importance as heirs to this extremely old lineage.”

The threat of global warming to much-loved species such as polar bears and penguins has been well-publicized. But Refsnider is concerned that the numbers of tuatara and other reptiles could dwindle without people taking enough notice. Tuatara, for instance, have hardly been heard of outside New Zealand or the rarefied world of herpetology, the study of reptiles.

“With species like polar bears and penguins, we call them charismatic mega fauna,” Refsnider says. “Tuatara certainly are not that. But lots of reptiles are temperature sensitive. A tiny increase in climate could potentially wipe out a species.

“Reptiles aren’t everybody’s favorite animals, so the things that affect them aren’t popularized,” she continues. “But the tuatara are ancient and unique. If we lose them, they’re gone forever.”