By John R. Platt, Source: Scientific American
Now here’s a great conservation success story: After more than 100 years, Galápagos giant tortoise hatchlings finally have a chance to thrive and survive on their native Pinzón Island, after conservationists cleared it of the invasive rats that nearly wiped out the animals.
Like most Galápagos giant tortoises—including the conservation icon Lonesome George, who died last year—the tortuga subspecies that once lived on Pinzón Island was nearly wiped out by the arrival of pirates, fishermen and invasive species in the seventeenth and eighteenth centuries. In this case, the greatest threat to the Pinzón Island tortoise subspecies (Chelonoidis nigra duncanensis) came in the form of voracious black rats (Rattus rattus) and Norway rats (R. norvegicus), which ate both the tortoises’ eggs and their defenseless hatchlings. Older tortoises can defend themselves against rats but so many young animals were killed by rodents that the subspecies could not replenish its population as older animals died off. By the beginning of the twentieth century, it appeared that no young tortoises on the island were surviving until adulthood.
Conservationists took the first step toward saving the Pinzón Island tortoises in 1965 by collecting as many of the animals as they could and placing them into captive breeding programs. Tortoises were then hatched and reared on other islands and brought back to Pinzón Island once they were old enough, but the impossibility of successful breeding on their home island led to the subspecies being classified as extinct in the wild.
The next step began a few years ago when Galápagos National Park and its partners launched a program to eradicate the rats and other invasive species throughout the archipelago, starting on smaller islands such as Pinzón, which as of last year was home to an astonishing 180 million rats. Last December more than 20,000 kilograms of poison were dropped on the 18-square-kilometer island. The poisons, which dissolve after a few days, were specially designed to attract rats but repel birds and other wildlife that might accidentally consume them. The rodents quickly took the bait and Pinzón has now been tentatively declared rat-free.
Late last month Galápagos National Park took the third step and returned 118 juvenile tortoises to Pinzón from a breeding center on Santa Cruz Island. It took 11 park rangers two and a half hours to carry the young tortoises over rocky terrain to place them in nests in their native volcanic soil. Last week, as conservationists looked on, the hatchlings started to emerge and explore their newly resurrected home. The young tortoises may represent the only healthy juveniles on Pinzón since before the year 1900. They join approximately 100 century-old tortoises and another 250 that have repatriated to the island over the last few years and range in age from five to 40.
The rat eradication project had numerous partners, including Island Conservation, the Charles Darwin Foundation, Bell Laboratories (not the lab of telephone fame), which manufactured the poisons, and The Raptor Center of the University of Minnesota, which is helping to preserve the native birds of the Galápagos. In a press release, Island Conservation CEO Bill Waldman called the tortoises’ return to Pinzón “a dream come true for conservationists around the world. We owe much to our predecessors who had the foresight to preserve this unique species in captivity.” Other animals that now have a new chance at survival on Pinzón include a recently recognized seabird species called the Galápagos shearwater (Puffinus subalaris), the Pinzón lava lizard (Microlophus duncanensis), and several species of other birds and iguanas.
Some risks remain, of course. Although the poisons dropped on Pinzón in December appear to have wiped out rats and other invasive rodents, the island will be monitored for two years to make sure none survived. Other islands where the poisons have been used so far appear to be rat-free, so the chances for Pinzón appear good. And now, even as the young Pinzón tortoises explore their new home, the project will move on to larger islands, including Floreana, which is 10 times the size of Pinzón and home to more than 40 threatened species. That project, which is slated for 2014 and will cost several million dollars, will be much harder due to the island’s human population. But if it succeeds, it will pave the way for other rat eradication projects on islands around the world—and hopefully save other endangered species like the ones that now have a new chance on Pinzón Island.