Island. The very word connotes isolation — an isolation that has allowed pockets of animal species to evolve in safety over the course of thousands of years. But, as author William Stolzenburg writes in a new book, isolation can also be a weakness.
In Rat Island: Predators in Paradise and the World's Greatest Wildlife Rescue, Stolzenburg gives an account of the damage done to island ecosystems by invasive species like cats, weasels and rats — all animals that have at one point overrun new island environments and nearly destroyed native species.
One species Stolzenburg focuses on is the kakapo, a large, green, nocturnal parrot that is found only in New Zealand.
Stolzenburg tells NPR's Renee Montagne that because its only predators were in the sky, the kakapo had no need to fly and, therefore, couldn't.
"It exuded this particular scent also that was supposed to attract other kakapos," he says. "Of course, when the invaders got to New Zealand — when the rats and the cats and the weasels came to New Zealand — this was a bird that was just set up for massacre, and that's exactly what happened."
Saving New Zealand's Kakapos
Stolzenburg explains that in the 1800s, settlers arriving in New Zealand brought sheep and rabbits with them for game. Sheep ate much of the vegetation, and the rabbits, being rabbits, exploded in population. With their huge numbers and voracious appetites, they began eating the sheep's rangeland. So to deal with the rabbit problem, settlers introduced stoats — a member of the weasel clan and a terrific predator. But the stoats quickly found much easier prey than rabbits — kakapos.
Kakapo numbers quickly shrank so that, once New Zealand's third most populous bird, they soon only lived in small enclaves scattered around the country.
The New Zealand government made its first efforts at saving the bird in the 1890s, when it appointed a hunter and self-taught naturalist by the name of Richard Henry to be the birds' caretaker. He was tasked with establishing a refuge for the birds on an island off the southwest corner of New Zealand, known as Resolution Island. Henry spent the next 10 years gathering up as many kakapos as he could find — over 500 — and releasing them on the island.
Unfortunately for both Henry and the kakapo, Stolzenburg says, Resolution Island was within swimming distance of the mainland — and stoats can swim. Ten years after he began his project, Henry discovered a stoat on the island and realized his life's work had been in vain.
Conservation efforts slowed after Resolution Island, with kakapo sightings few and far between. But in the mid-20th century, the New Zealand government renewed its efforts to save the bird.
Conservationists were disheartened by their first efforts to find the parrots — old kakapo haunts were empty, and only a handful of birds were located. But an expedition in the 1970s was lucky enough to come across a population of close to 200 birds. It was the mother lode of the remaining kakapo population, and it provided conservationists with another opportunity to rehabilitate the species.
They began incubating the kakapos, protecting and guarding their eggs, and setting traps to ensure that no predators could get to the birds. But eventually, Stolzenburg says, even that sanctuary was invaded by feral cats. So scientists staged an emergency rescue and moved most of the remaining kakapo to Codfish Island, which had been cleared of all predators.
"It is basically about as pristine as you can find in New Zealand," Stolzenburg says. "They are now basically refugees; they're exiles from the mainland, and they are living their lives out on this island where they are being watched 24/7 by kakapo rangers who make sure that every egg, every mating now is a grand event, and they are watched very closely."
In Alaska, A 'Perfect Score' For Rats
Stolzenburg says there have been other, similar catastrophes across the globe. In the United States, Kiska — part of the Aleutian Islands off the coast of Alaska — was a pristine island environment until World War II, when the Japanese invaded and the U.S. became intent on taking it back.
Troops were sent ashore on Kiska, and at some point during their deployment, several rats also made their way onshore. Over the intervening years, the rats crossed 12 miles of rocky terrain — including a more than 4,000-foot volcano — and made their way to one of the world's most spectacular colonies of seabirds.
Known as auklets, Stolzenburg explains that the seabirds are tiny — about the size of a robin — and travel Kiska once a year to reproduce and nest in the crevices of the hardened volcanic rock.
"This was a perfect, perfect score for the rats," he says.
Here was this tremendous food supply that arrived every year, like clockwork. The rats would tear into the colony and massacre the auklets, hoarding them to survive the harsh Kiska winters.
Naturally, Stolzenburg says, scientists are concerned about the long-term impact the rats might have on the auklet population. Attempts to eradicate the rodents — largely with poison — have been difficult due in part to the island's remoteness as well as its rugged nature. The volcanic rock formations have essentially created a safe haven for the rats, and the logistics involved in dropping rodenticide over 100 square miles of terrain would require a gargantuan expedition — and one that is not guaranteed to succeed.
Between the auklets of Kiska and the kakapos of New Zealand, scientists have reason to both hope and be cautious. Stolzenburg says the islands essentially serve as metaphors for how the world's invasive species can irreparably alter fragile ecosystems.
"We have a very clear view of what's going on, and these islands provide that," he says. "It puts it on us. We put them in this position. Now we have a decision to make. We can either stand back and say, 'Let nature take its course,' or we can decide that this is our responsibility and do something about it."