How We Almost Lost the Island Fox

The once-endangered species made the fastest recovery ever recorded for a mammal—but first, conservationists had to kill some pigs and relocate some eagles.

Christie Boser, an ecologist with the Nature Conservancy, conducts a health test with a fox. (Nancy Crowley / The Nature Conservancy)

Only six kinds of fox live in all of North America, and—speaking objectively—the island fox may be the cutest. It lives only on the Channel Islands, an archipelago off the coast of Southern California, and like many other island-inhabiting creatures, it has miniaturized over the millennia. Even adults are smaller than housecats. And unlike their mainland relatives, they are diurnal, with little fear of humans.

“They’re so easy to handle,” says Gary Roemer, an ecologist at New Mexico State University who wrote his dissertation about the animals. “You stick your hand in the trap, grab them by the scruff, pick them up, and they roll over.”

A little more than 20 years ago, Roemer watched the docile fox almost disappear completely. In only seven years, fox populations across three of the six islands plummeted, the animals driven to the brink by a pair of invasive species. On a fourth island, Santa Catalina, a virus decimated its population.

By the time conservationists began trying to rescue the foxes in 2000, only 55 foxes lived on Santa Cruz island. On the two other northern islands, the population had dwindled to 15. Soon after, four subspecies of the island fox—there are six subspecies over all, one per island—were declared endangered.

That year was, thankfully, a low point. Today, more than 2,100 foxes now live on Santa Cruz.  On the northern islands, Santa Rosa and San Miguel, the population has risen to 1,200 and 700.

Last week, the U.S. government removed three subspecies of the island fox from the endangered species list. It “down listed” a fourth subspecies—the one on Santa Catalina island, stricken by a virus—moving it to the less precarious “threatened” register. In the four-decade history of the Endangered Species Act, no mammal has recovered faster than the island fox.

Scott Morrison, a biologist at the Nature Conservancy who was involved in the recovery, called it a “timely dose of hope for our undertaking.”

“So many of the iconic terrestrial animals out there are looking at a pretty grim future. The big herbivores, the big cats, the bears,” he said. He cited a recent study in Bioscience that warned current conservation efforts were underfunded and failing. “I’m hoping this energizes other folks out there who are working on behalf of other imperiled species in the world.”

But Roemer, who discovered the mechanism that imperiled most of the foxes, wonders if the species could have avoided endangerment in the first place. His history with the animals goes back to 1993, when he moved to Santa Cruz island to study the island foxes. A doctoral student, he was trying to model the fox population to learn whether the animals mated monogamously. The study proceeded happily for nine months—until one afternoon, when he found a radio-collared fox dead, its side gored by talons.

Golden eagles sometimes circled overhead, he remembered. “I thought, goldens must come over to the island every so often, and they bump off a fox,” he says.

In reality, he had found the first sign of an ongoing ecological collapse. More dead foxes started turning up. When he started the research, Roemer had monitored two different fox populations on two different parts of Santa Cruz; by 1995, both were crashing. Park biologists elsewhere in the chain reported similar collapses. (All six islands are controlled by the National Park Service.)

Island foxes weren’t the only vertebrates on the island: a feral pig population, introduced in the mid-19th century, also ran wild. One day, exiting his Jeep, Roemer saw a golden eagle take off from the side of a mountain. Blood dripped from its beak and talons. When he went to investigate, he found a dead piglet, gutted from its gullet to its groin.

Nancy Crowley / The Nature Conservancy

By the mid-1990s, ecologists had started to hypothesize about a phenomenon endemic to island ecosystems. It started with a question: Why did invading rabbits frequently devastate the islands where they had been introduced? It wasn’t just that the bunnies chowed through local vegetation, crowding out other plant-eaters. Carnivorous vertebrate populations also seemed to crash after the rabbits showed up.

Researchers started to sketch a hypothesis called hyperpredation. In island ecosystems, the idea went, local invasive predators would gorge themselves on a small and easy-to-catch invasive prey. As more predators survived on the glut of convenient food, they would start going after the local endemic prey. That species, suddenly dealing with many more predators than usual, would start to crash.

The hypothesis neatly matched the massacre unfolding in the Channel Islands. Golden eagles made themselves at home on the islands by chowing down on feral piglets. The fat, small piggies provided cheap and easy calories. But as golden-eagle numbers swelled, they started occasionally going after the island foxes. From then on, the fox’s fate was sealed. Ecologically, pigs are more resilient than the foxes: They reproduce multiple times per year and have large broods, while foxes only gestate annually and have one or two kits. Pigs also eventually grow too large for the eagles to catch, while the naturally dwarfed foxes remain bite-sized.

Roemer identified this mechanism by 1995 and began to push for the removal of golden eagles. But it wasn’t until 1998, he says, that the National Park Service conducted a study elsewhere in the chain to check on local island-fox populations. They too had cratered: Traps distributed across the island caught nine foxes in one night, when they would usually turn up between 20 and 40. A year later, the National Park Service—in conjunction with the Nature Conservancy, which owns most of Santa Cruz island—got serious about saving the animals.

Yet ravenous eagles and oblivious pigs were not the only threat facing the fox. On Santa Catalina island, the number of foxes had also plunged, from thousands to 103 in 1999. Santa Catalina is the only channel island with a permanent town and resort. Thousands of people visit its beaches every year, ferrying over from L.A. Golden eagles never moved into Santa Catalina island—instead, dogs accompanying these visitors (or perhaps a hitchhiking raccoon) brought a plague of the canine-distemper virus. The local subspecies of island foxes had no natural immunity to the disease, and it swept through the population.

This led to a straightforward but logistically onerous solution: Vaccinate the animals. On Santa Catalina island, conservationists now vaccinate that entire fox population with rabies and canine-distemper shots. It is a rare step meant to help the fox continue to rebuild its population.

For the northern three islands, the recovery program was more complicated. Righting the ecological wrong entailed three steps: First, park rangers and conservationists captured the surviving foxes and began a captive-breeding program to reinvigorate the fox population. Second, they began capturing and transporting the golden eagles off the island. Finally, they culled the island pig population, removing an invasive species that had thrived on the islands for more than a century.

Eradicating the pigs was particularly controversial. In 2005, Michael Markarian, the current chief operating officer of the U.S. Humane Society, published an op-ed in the San Francisco Chronicle criticizing the culling. “Wildlife agencies have adopted a certain zealotry in wanting to exterminate any animal species that hasn’t been here for an arbitrarily determined amount of time,” he wrote.

Foxes have lived on the northern islands approximately 15,800 years longer than the the feral pigs have, a period of time spanning well into the last Ice Age. “When conflicts occur between species, we should do everything we can to make sure lethal control is only a last resort, and that animal welfare is an important part of the equation,” says Markarian in a statement yesterday.

“It was just surprising how the necessity of removing pigs wasn’t a widely shared viewpoint,” says Morrison. “You would not be able to get to the point where we are right now, and let the foxes be foxes, if you didn’t deal with the feral pig problem.”

The benefit of pig removal has rippled throughout the island, he added. “A lot of really rare plants that are also endemic to the islands are rebounding, because they’re not being eaten by the pigs. My hunch is that, in the not-so-distant future, we’re going to see more delistings cascading from the effort of this delisting.”

The Nature Conservancy is also trying to reintroduce bald eagles to the islands. Bald eagles dine mostly on marine wildlife, and they don’t pose a major threat to the foxes. In fact, Morrison said that bald eagles lived on the island until the 1950s, when DDT weakened their egg shells and they were locally extirpated. After that, golden eagles began to fly over from the mainland, filling the niche they vacated.

Nancy Crowley / The Nature Conservancy

In last week’s adjustment, Santa Catalina foxes—the subspecies stricken with canine distemper—were only “down listed,” moved from the endangered list to the threatened list. “Right now, it’s really difficult to abate the threats to that fox population,” says Morrison, which is why the Nature Conservancy continues its vaccination program. For now, a raccoon or dog could always re-introduce the disease and obliterate the population again.

Vaccination is an uncommon step among conservationists, but it has some precedent: Biologists vaccinate all California condors against West Nile virus, due to the enormous threat to that animal.

For his part, Roemer is relieved that the foxes have recovered. But he believes that if the National Park Service had acted sooner, the fox might have avoided ever becoming endangered. By September 1995, the government had been informed that invasive golden eagles were decimating fox populations, he says. When asked by the U.S. Fish and Wildlife Service to comment on the delisting, he noted that the golden eagles were not studied on other islands until late 1998. The first eagle was not removed from the islands until November 1999.

“They screwed up,” he told me. “Four years isn’t that long a time, for people, but animals can go extinct in that long a time.”

He believes the first golden eagles only established themselves on Santa Cruz island a few years before he got there, in the late 1980s or early 1990s. It’s possible that a mating pair did not take up residence until 1993. If the Park Service had removed golden eagles in 1996, island fox populations never would have plummeted. Specifically, he says, the government would never have had to initiate the extremely expensive captive-breeding program.

The island fox isn’t totally in the clear yet. One of its biggest dangers follows directly from once-miniscule population size: All of its subspecies have very little genetic variability. It’s a classic case of bottlenecking: The 2,100 foxes on Santa Cruz Island currently only contain the genetic diversity of the 55 foxes that survived the 1990s.

This is not a new problem for the island fox. A study last year found that the island fox subspecies from San Nicolas island—which was never declared endangered—has almost no genetic variability to speak of. When researchers sequenced its genome, they found that its individuals are nearly identical. It is the least variable sexually reproducing species ever described. “They’re almost like clones, practically,” says Roemer.

Some researchers have therefore begun to propose relocating animals across islands—a technique known as genetic rescue. It has worked elsewhere before, and it could inject each subspecies with enough variation to make it more vigorous.

It may seem like the ultimate in modern-day stewardship: Biologists ferrying small foxes across the sea, all for the good of the species. But modern-day ecologists will be repeating a more ancient exercise. While genetic evidence suggests that island foxes floated or swam to the northern islands during the previous ice age, when sea levels were lower, they did not reach the southern islands without help. Between 6,000 and 4,000 years ago, Native people, likely the Tongva, carried island foxes between the islands as companion animals. In particular, it seems increasingly likely that people introduced foxes to Santa Catalina and the southern isles.

In the long view, the story looks less like people disturbing a pristine environment and then rushing to remedy their own failure. Instead, it suggests a longer story of human-fox coexistence. Without human help, there wouldn't be island foxes anymore. And without humans in the first place, these particular kinds of island fox might not have existed at all.