Kneeling in the dirt beneath a sycamore tree, Christie Boser cradled the endangered island fox in her lap, firmly gripping its neck with a gloved hand while using the other to slip on a green blindfold that would keep the animal calm.
It had been captured the night before, lured into a metal cage by the scent of cat food and the promise of an easy meal. After weighing the creature, Boser ran a flea comb through its reddish-gray fur, massaged and petted its lean body, and probed its mouth to gauge its condition.
"All his claws look nice and pretty ... but he has a broken canine," said Boser, a scientist with the Nature Conservancy and the restoration manager on Santa Cruz Island, the largest in the chain of eight Channel Islands off the coast of California.
After a brief exam, Boser released the yearling fox, which scampered off and vanished into some nearby shrubs.
It wasn't too long ago that such a routine checkup was a lot less commonplace. One of America's rarest mammals, found only on six Channel Islands, the island fox was driven nearly to extinction in the 1990s by predatory golden eagles. By 1999, there were only about 85 island foxes left on Santa Cruz Island, while nearby San Miguel and Santa Rosa Islands were each down to about 15.
Today, the species is on the verge of a dramatic recovery—one of the fastest in the history of the Endangered Species Act—with nearly 2,500 on the Channel Islands.
"They were listed as endangered in 2004, and they're pretty much ready to come off that list at this point," said Timothy Coonan, a biologist with the U.S. National Park Service (NPS), which works with the Nature Conservancy to preserve resources on Santa Cruz Island.
Threat From the Skies
Scientists think the island fox is descended from mainland gray foxes that arrived on the Channel Islands sometime between 6,000 and 10,000 years ago, and that the animal's body shrank in size because of limited space and resources.
"It's probably the best known example of island dwarfism," Coonan said.
On the islands, the smaller foxes quickly differentiated into six new subspecies. Free from predators, they thrived until until the 1990s, when golden eagles arrived.
Historically, golden eagles never bred on the Channel Islands, but some do occasionally make the 25-mile (40-kilometer) trek from the California mainland.
In previous times, golden eagles arriving on the Channel Islands would have likely been chased off by bald eagles, which are intensely territorial. But the Channel Islands' bald eagles had been decimated decades earlier by the insecticide DDT, Coonan explained. From the 1940s to about the 1970s, chemical companies discharged millions of pounds of DDT into the ocean, where it contaminated the bald eagle's marine food supply.
In the '90s, golden eagles were drawn to Santa Cruz Island by its burgeoning feral pig population. The descendents of domestic farm animals brought to the island in the 1850s, the pigs provided a steady food source for the raptors.
"What the golden eagles were really depending on were the pigs. The foxes were kind of an ancillary snack," said Kate Faulkner, chief of natural resources management for Channel Islands National Park.
The loss of bald eagles, the arrival of golden eagles, and the island's thriving feral pig population created "a perfect storm of events" that nearly doomed the island foxes, Coonan said.
Sleepy Juice and Robo-Dogs
The crisis spurred a recovery effort by the NPS and the Nature Conservancy, which owns 76 percent of Santa Cruz Island. "We went to the wall on the island foxes," Coonan said. "In the park services, we're mandated to save everything entrusted to our stewardship. If we let the island foxes go extinct, we might as well not be here managing anything."
Captive-breeding programs were established on Santa Cruz, Santa Rosa, and San Miguel islands. Contract hunters were brought in to remove the non-native feral pigs and sheep, which had stripped the islands of vegetative cover for the foxes.
And bald eagles—which feed mainly on fish and don't affect the foxes—were slowly reestablished on the islands while golden eagles were captured and released back on the mainland.
That last task proved especially challenging. "The last golden eagle pair was really tricky to get because they had seen all their buddies get captured," said the Nature Conservancy's Boser.
After increasingly creative attempts to catch the birds—including using a fake egg filled with a sedative that Boser called "sleepy juice," and a robotic dog dressed up to look like a fox, the final golden eagle pair was netted by helicopters in 2006. In total, 44 golden eagles were removed from the islands.
The night the last golden eagles were captured, Boser and her colleagues celebrated atop a mountain on Santa Cruz Island. "A collective cheer echoed across the Santa Barbara Channel," Boser said.
With the feral pigs and the golden eagles gone, the fox population rebounded—and with a swiftness that stunned even the scientists and conservationists involved.
Today there are about 1,300 foxes on Santa Cruz Island, 500 on San Miguel Island, and 600 on Santa Rosa Island, with each population having a 90 percent annual survival rate.
"It's a strange thing," Coonan said. "The official recovery plan has not even been finalized [by the U.S. Fish and Wildlife Service], and yet these populations are doing so well that they can come off the endangered species list."
Brian Hudgens, a research ecologist at the Institute for Wildlife Studies, which ran the fox captive-breeding program, agreed that some of island fox subspecies are just about ready for delisting.
"For the subspecies on San Miguel and Santa Cruz, their populations are large enough and they are doing well enough that they are no longer in danger," Hudgens said. "Santa Rosa is almost there. It'll probably take a couple more years."
The work to save the island fox is far from over, however. The Nature Conservancy and the NPS continue to monitor the foxes, keeping an eye out for dangers like pathogens and parasites, as well as looming threats such as climate change.
Another potential concern is genetic health. Despite rebounding to their predecline numbers, the species was so severely culled that the amount of variation in its gene pool might have been compromised.
Such a "population bottleneck" could impact the fox's ability to deal with disease or environmental change, said Gary Roemer, a biologist at New Mexico State University who has studied the island foxes.
One controversial solution would be to interbreed different subspecies of island foxes, Roemer said. A similar strategy was recently used to bolster the genetic health of Florida panthers, drawing on DNA from cougars from Texas.
Coonan said he is happy to shift from worrying about the fate of the foxes to monitoring their health.
"It's actually a great stage to be here in the island recovery," he said. "I can sleep a little bit more at night because of everything that's gone on."