The Primitive Science of Restoration
Biologists seek to “do no harm,” improve island health, get rid of human-introduced predators and untangle complex relationships that developed on the fly.
This article originally appeared on Nov. 16, 2009.
In the northern Channel Islands off California, a cat-sized native fox is making a dramatic comeback, thanks to a 10-year, $22 million multifaceted program to save it from extinction.
The last of the resident golden eagles, a nonnative species that was snacking on foxes like kids in a candy store, was removed in 2006 and transported to the far-off northern Sierra Nevada. Also, fish-eating bald eagles, a territorial sort that was once native to the islands, were reintroduced to help chase off its red-meat-eating cousins.
It’s just one piece of a Herculean effort by the National Park Service and The Nature Conservancy to turn back the clock, untangle scrambled ecosystems and restore some of the wildness that was lost when the islands — often called California’s Galápagos — were settled by European ranchers in the mid-19th century. For the first time in 160 years, the rats, sheep, pigs, horses and cattle are gone, and the birds and plants are rebounding. The project is also another excellent example of just how hard it can be to re-establish some baseline condition from the past.
Today, there are nearly 1,000 foxes on Santa Cruz Island, more than 300 island foxes on San Miguel Island and 400 on Santa Rosa Island. That’s way up from fewer than 90 foxes on all three islands in 1999, though not yet as high as the roughly 2,600 foxes there were 1993.
“The populations in the wild are doing great,” said Tim Coonan, the park biologist. “They increased at a fantastic rate.”
Yet, mysteriously, even with all the golden eagles gone, eagles still prey on a few island foxes. Since 2006, when the last golden eagle was removed, biologists have found 14 foxes killed by eagles — seven each on Santa Rosa and Santa Cruz, including at least one this year.
It’s not enough mortality to threaten the now stable fox populations, but it’s enough to make scientists scratch their heads. Are the culprits a few golden eagles on rare trips to the island, or are bald eagles now eating foxes? Bald eagle feathers have been found in two fox carcasses on Santa Rosa.
Mark Rauzon, a professor of geography at Laney College in Oakland, Calif., and a consultant with 30 years’ experience in island restoration in the tropical Pacific Ocean, likens the field to surgery in its early, primitive years, when the science was crude at best.
“We’re doing island surgery,” Rauzon said. “It’s ‘do as little harm as you possibly can,’ with the ultimate goal of adding more ecosystem health. It’s impossible to know how it’s going to go. We can’t really restore to anything that was in the past. We’re taking the responsibility of being practitioners for a new regime.”
In 2004, Rauzon oversaw the eradication of nearly 300 wild cats on Wake Atoll, a U.S. possession and military base in the North Pacific where, by his estimate, the cats were killing or injuring 30,000 native seabirds per year. At the time, Rauzon said, the military did not have the funding for another eradication program, this one to get rid of the rats.
“People say, ‘You shouldn’t have started this then,’ ” Rauzon said. “But if we hadn’t done it, nothing would have changed. You have to strike.”
Since 2004, colonies of shearwaters, terns, tropicbirds, frigatebirds and boobies have returned to pre-World War II levels on the 6.5-square-kilometer atoll, Rauzon said. Without the cats, however, the rats have become a conspicuous nuisance, and the base is reviewing a plan to get rid of them.
“It’s important to finish what you start,” Rauzon said. “If you don’t, everything would have died in vain.”
On the now inappropriately named Rat Island in the Alaska Maritime National Wildlife Refuge, the U.S. Fish and Wildlife Service spent $3 million last fall to poison the rats and bring back the seabirds. Sure enough, some colonies of seabirds have started breeding on the island again. But officials can’t explain why they found so many poisoned birds on survey this spring — 227 birds in all, including 41 bald eagles.
Brad Keitt, director of conservation for Island Conservation, a Santa Cruz, Calif.-based nonprofit organization that has carried out eradications on 40 islands, including Rat Island, said the long-term benefits always outweigh the short-term setbacks.
“Islands are at the epicenter of the extinction crisis,” Keitt said. “If we don’t do anything, a death will occur every time a bird flies to one of these islands. Either the adult gets eaten or the egg it’s laying gets eaten. We can stop the chain of destruction.”
On Macquarie Island, halfway between Australia and New Zealand, the Parks and Wildlife Service of Tasmania came under fire earlier this year for failing to eradicate the island’s population of rabbits when it got rid of the cats in the 1990s. Researchers said that in the absence of cats, the rabbits bred out of control, stripping much of the vegetation that the seabirds used for cover.
In response, other researchers said the seabird populations on Macquerie had benefited from the cat eradication, and that anyway, the technology had not existed in the 1990s for large-scale rabbit removal. Also, they said, the rabbit population is presently in decline, suggesting that other factors besides cat removal were affecting the numbers.
Next year, Tasmania will embark on a program to poison, fumigate and shoot 130,000 rabbits on Macquarie and kill off 36,000 rats and 103,000 mice.
Because of the experience at Macquarie, scientists expect there will be a strong push at the next world conference on island restoration, set for New Zealand in February, to learn more about how to conduct eradications of multiple nonnative species and predict the outcomes.
Eagles and Foxes, Redux
Bald eagles, once native to the Channel Islands, were wiped out by egg collectors, hunters and DDT by 1960. Today, between 30 and 35 of the birds make their home on the island and can be observed in their nests live on the Web.
During the debate over how to bring back the fox population, Paul Collins — curator of vertebrate zoology at the Santa Barbara Museum of Natural History and the co-author of a new study on the island fox recovery program — predicted that bald eagles, once reintroduced, might occasionally eat a fox. Now, he believes his prediction may have come true.
“There’s a good chance that we’re having predation from bald eagles,” he said. “They may be feeding on dead carcasses they find. Or they may be chasing them down and catching them. It’s not something we didn’t expect.”
Others say there’s no way bald eagles, a species native to the islands and known to eat mostly fish, could be preying on foxes. It’s much more likely, they say, that the guilty party is a transient golden eagle flying out from the mainland. Bald eagles are known scavengers, which could explain the presence of their feathers on fox carcasses.
“There’s absolutely no evidence that bald eagles take island foxes,” Coonan said. “We absolutely don’t believe bald eagles are responsible for any of that.”
Back in 1999, scientists had to sort out a much thornier problem in the northern Channel Islands. The success of the fox recovery hinged on deciding which invasive species to get rid of first. The fox population was crashing. Golden eagle predation and not disease was determined to be responsible. There were only 15 foxes each on Santa Rosa and San Miguel, and only 60 on Santa Cruz, and the park began trapping them as fast as possible to breed them in captivity.
The golden eagles had been attracted to the islands by thousands of wild pigs on Santa Cruz, another invasive species. But which should be removed first?
Some said the pigs should go first so that the eagles would leave and save the expense of capturing them live. Others reasoned that if the pigs went first, the eagles would simply eat more foxes — and this hypothesis prevailed.
There were calls to shoot the birds, but that would have been both a public relations disaster and physically difficult. Ultimately, it took six years to capture and relocate 32 increasingly savvy adult eagles. The last elusive birds had to be followed around by helicopters until they got tired and flopped on the ground, where they could be covered with nets.
At the same time, bald eagles were introduced to the islands in hopes that they would not allow golden eagles into their territory. Then, toward the end of the golden eagle removal, the park and the conservancy began killing 4,800 pigs.
Collins and his co-authors, Gary Roemer, an associate professor of wildlife and conservation ecology at New Mexico State University, and Brian Latta, executive director of The Bird Group, a nonprofit organization based in Santa Cruz, Calif., titled their recent study, “Does the Order of Invasive Species Removal Matter? The Case of the Eagle and the Pig.”
Based on an examination of the contents of golden eagle nests, they found that the pair of eagles that had escaped capture the longest tripled its consumption of foxes after the pigs were gone. It was positive proof of the early hypothesis for removing the eagles first.
“It’s been a jigsaw puzzle, but one that was workable,” Collins said. “You could actually figure out how the pieces fit together.”
As for the handful of foxes still being eaten by eagles, Peter Sharpe, a wildlife biologist with the Institute for Wildlife Studies, said golden eagles might be flying out to the islands during the annual deer and elk hunts on Santa Rosa. On Santa Catalina Island to the south, bald eagles have been coexisting with foxes for more than 25 years with no signs of predation, Sharpe said.
Lotus Vermeer, director of the Santa Cruz Island Preserve for The Nature Conservancy, said that bald eagles “harass the heck out of golden eagles” and were affording better protection to foxes. No golden eagles have established a nest on Santa Cruz since 2006, and none have been seen there for at least a year, Vermeer said.
“Bald eagles have been a very effective deterrent to golden eagles on the islands,” she said.
But that doesn’t mean that a bald eagle would never kill a fox, Collins said. The historical record shows that egg collectors found pieces of foxes in bald eagle nests on the islands at the turn of the century, he said. In addition, Collins said he found six fox bones — out of 10,000 bones — in a 60-year-old bald eagle nest on San Miguel. Mammals may comprise 14 percent of the bald eagle diet, he said. Video taken on Catalina shows them bringing live wild piglets and goat kids to feed their young in the nest.
Roemer said, “Reintroduction of bald eagles was a good idea, but maybe it would have been more efficacious to do it last. When you’re faced with these complex issues and interactions between invasive and native species, you have to consider all the potential outcomes.”