The Amazing, if Tentative, Recovery of the Island Fox

In the centuries since European powers first colonized North America, only a single mammal species, the sea mink, has gone extinct.

Our continent will no doubt witness another mammalian extinction, and other species have surely come close, but no mammal has been listed as endangered and then recovered as fast as the island fox.

Last week, US Fish and Wildlife Service officials announced a proposal to de-list three of four island fox subspecies that were first listed on the Endangered Species Act just twelve years ago.

First, some background. The island fox, Urocyon littoralis, is only found on six of California's eight Channel Islands: Santa Rosa, San Miguel, Santa Cruz in the northern cluster, and San Clemente, San Nicholas, and of course Santa Catalina in the southern group.

Descended from the mainland grey fox, nobody knows exactly how the canids first wound up on the islands, but we do know it happened between seven and ten thousand years ago. Once there, life was easy for the foxes. Unlike on the mainland, the critters had no predators to worry about, and there were plenty of native skunks and mice to eat. Eventually, the foxes spread to inhabit the six islands on which they're found today, no doubt aided by humans. As so many species do on islands, the foxes would eventually shrink relative to their mainland counterparts, resulting in the adorable animals we know today. For thousands of years, the foxes flourished. And then we happened.

In 1999, a survey across all six fox-bearing islands found population declines of 90 to 95 percent. There were just 15 foxes left on San Miguel and another 15 on Santa Rosa. Santa Cruz was down to just 55 foxes and Catalina had just 103, down from 1,342 five years earlier. At the time, biologists estimated that the species had a 50 percent chance of extinction over the next five to ten years. It was easy to figure out why the Catalina foxes were dying. Hundreds of people travel to and from the island each day, and on one fateful day, a raccoon would stow away on one of the boats. That raccoon carried a strain of canine distemper virus with it, a disease to which the island foxes were unaccustomed. With immune systems unprepared for the fight, Catalina's subspecies rapidly succumbed to the illness.

On the three northern islands, the decline was not due to a sneaky raccoon, but to golden eagles. The introduction of feral pigs on Santa Cruz Island and mule deer and elk on Santa Rosa Island provided a study supply of prey for the hungry birds. As the islands' native bald eagles declined due mostly to DDT exposure, golden eagles (who did not eat the same tainted fish that their bald cousins dined upon) were able to establish permanent nests from which they could easily scoop up the curious foxes as well. Having evolved without predators, island foxes weren't savvy enough to escape the piercing talons of the massive raptors.

Once the dire situation was discovered, a fox consortium came together, made up of all the agencies that manage lands on which the foxes are found: the Catalina Island Conservancy, the Nature Conservancy (which is in part responsible for Santa Cruz Island), and the National Park Service (which manages the rest of Santa Cruz, plus Santa Rosa, and the Navy-owned San Miguel), plus FWS.

(San Clemente and San Nicholas are both owned and operated by the US Navy; while their sub-species were never listed under the ESA, the FWS and the Navy together signed a "Conservation Agreement" regarding the implementation of conservation measures to safeguard the future of these unique populations as well.)

The agencies worked together to remove golden eagles from the northern islands and to remove the pigs, deer, and elk that provided prey for those eagles. They vaccinated the foxes against canine distemper virus and conducted a captive breeding program to repopulate each of the islands. Since the captive breeding program ended, the agencies have continued to work together on monitoring the islands' fox populations and re-establishing bald eagles to their historic territories.

"The remarkable recovery efforts of land managers and conservation partners over the past two decades on behalf of the Channel Island fox is the reason for this historic recovery success," said Dan Ashe, Director of the U.S. Fish and Wildlife Service.

The rebound has been so successful that FWS is proposing the removal of the San Miguel, Santa Rosa, and Santa Cruz sub-species from the ESA entirely, though monitoring efforts will still occur. By delisting them, federal funding will be allocated to other species that require attention.

The proposal for the Catalina sub-species involves reclassifying them from "endangered" to "threatened." Despite their impressive recovery (in 2013, Catalina had 1,852 foxes, an improvement compared even to pre-decline levels) Catalina foxes aren't out of the woods.

Indeed, human activities remain a threat to the long-term survival of the charismatic mammals on the tourist-heavy island. "Conservation work is never done, especially on an Island visited by nearly one million people each year," said Julie King, Director of Conservation & Wildlife Management for the Catalina Island Conservancy. "Each year, several foxes drown in uncovered water containers, become trapped in trash cans, are injured or killed by unleashed dogs, are hit by vehicles, or die from the ingestion of rat poison or other toxins." And then there's a mysterious epidemic of ear cancer now spreading through the Catalina population. Nearly half of dead foxes examined between 2001 and 2008 had tumors on their ears, a trend that King and her colleagues are working to understand.

"By being reclassified rather than delisted, these foxes will still enjoy certain legal protections from the Endangered Species Act," she adds.

All sub-species will remained listed as threatened by the State of California, but that's related to their limited range and naturally small population sizes, not to any particular population decline or threat. Each agency will continue to monitor the foxes on each of the islands. 

The ongoing scientific research doesn't just benefit these foxes. Other endangered canids, like Ethiopian wolves or African painted dogs, suffer from similar disease epidemics but are much harder to study. Because Catalina's foxes aren't wise enough to avoid predators, they're also not wise enough to avoid the traps that researchers use to monitor them. And the same animals allow themselves to be trapped year after year, offering a long-term catalog of fox health information, something possible nowhere else in the world. Lessons learned from studying island foxes will hopefully become useful for conservationists working with other rare species. "We're lucky that we have such trap-happy animals," King says.