| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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Feature Fix It for the Foxes An Island Ecosystem Resuscitated Small as it is, the island fox is tough to hide. Its vibrant coat of cayenne and black pepper stands out even through the Channel Island’s thick greenery. With a wash of white salt on its belly, and sprinkles on its nose, weighing in at four pounds and topping out at twelve inches, the fox looks more like a toy than a menacing predator. But this diminutive animal is armed with an arsenal of well-tuned senses. Keen nose quivering in the air, it scans the brush with piercing black eyes, swiveling its pointed ears to pick up any trace of prey. California’s Channel Islands archipelago is the only home the fox has ever known, and where it has claimed top dog status for thousands of years. Its lineage traces back to a much larger cousin, the mainland gray fox. Today, 10 to 40 miles of ocean swells separate the Channel Islands from the gray fox’s Southern California home. But during the last Ice Age, the landscape looked dramatically different. Lower ocean levels 18,000 years ago narrowed the width of the Santa Barbara Channel separating the islands from the mainland to about four miles, and land bridges joined the three northern islands into a single landmass known as Santarosae. Gray foxes likely first hitched their way to Santarosae on debris such as tree trunks swept across from the mainland by currents and storms. But the castaways weren’t well suited to island living. Where size was a plus on the mainland, it became a liability on the islands, where territories were small, food and water scarce, and predators absent. Natural selection favored the survival of smaller individuals. As each generation gave rise to the next, isolation and evolution resulted in a new dwarf species, Urocyon littoralis. Evolution didn’t stop there. Like Darwin’s celebrated Galápagos finches, the fox’s family tree sprouted a tangle of new branches. Several forces, both human and natural, separated the foxes into six discrete populations. A rising ocean divided Santarosae into Santa Rosa, San Miguel, Santa Cruz, and Anacapa islands. With the exception of Anacapa, each island supported its own fox population. Thousands of years later, Native Americans brought foxes to three of the southern Channel Islands—Santa Catalina, San Clemente, and San Nicolas. Isolated by time and geology, the six secluded fox populations evolved into separate subspecies varying in size, muzzle shape, and fur color. They even have different numbers of vertebrae in their tails, ranging from 15 in San Miguel to 22 for the San Nicolas foxes. Stocked with plentiful prey—birds, mice, and insects—and free of most predators, the islands proved a haven for the foxes. With no need to hide from stronger carnivores, they hunted day and night in the oak forests and thick chaparral. For thousands of years, the fearless animals flourished in their tiny Eden. But in the 1990s, the foxes of Santa Cruz, Santa Rosa, and San Miguel islands began dying off in huge numbers. Close observation revealed that the foxes’ decline was only one link in a chain reaction ignited by human interference. The meddling nearly succeeded in unraveling the islands’ ecosystems. Now the National Park Service, the U.S. Fish and Wildlife Service, and the Nature Conservancy have joined forces in a multimillion dollar effort to save these unique animals from extinction and restore the delicate ecosystems of the Channel Islands to their natural state. The story of the foxes’ decline began with the arrival of Spanish missionaries, who brought goats, dogs, sheep, pigs, and cats with them to the islands. All were eventually abandoned on the islands, where they have since multiplied into an ecological menace. The pigs have fared especially well by digging up the succulent roots of native plants. Their tilling erodes the soil, destroys native plants, and creates a hospitable environment for invasive plants such as wild fennel. “They’re basically hell. They’re little devils, that’s what they are,” says Erik Aschehoug, wildlife biologist for the Nature Conservancy, which owns a large percentage of Santa Cruz Island. Still, the pigs themselves did not threaten the island foxes. In fact, the animals coexisted fairly peacefully for more than 100 years. Fast forward to the 1940s, when the Southern California-based Montrose Chemical Corporation began dumping waste containing the pesticide DDT into the ocean near Santa Catalina Island. The company continued the practice for 30 years, eventually fouling the ocean floor with about 1,800 tons of the poisonous chemical. DDT soon permeated the marine food chain. Among the most affected were the bald eagles, which once soared at the top of that chain. After feeding on contaminated fish, sea lions, and sea birds, the eagles laid thin-shelled eggs easily crushed during brooding. Unable to reproduce, the Channel Islands’ bald eagles vanished within 20 years. The demise of the bald eagle, coupled with the abundance of feral pigs, opened a window of opportunity on Santa Cruz for a new predator, the golden eagle. Historically, territorial bald eagles probably kept the golden eagles at bay, says Brian Latta, head of the Santa Cruz Predatory Bird Research Group (based at the University of California at Santa Cruz). The bald eagles had fed largely on seafood spiced up only rarely with an island fox. By contrast, golden eagles feed primarily on small terrestrial animals that Santa Cruz Island historically held in short supply. But the feral pigs’ tiny, tasty piglets provided golden eagles with plentiful prey. Each year for the golden eagles, feast turned quickly to famine as the spring piglets grew larger and more difficult to hunt. Casting their menacing shadow on the brush below, the eagles homed in on the island fox instead. Signs that the golden eagles were preying on the foxes appeared in 1993, says biologist Gary Roemer of New Mexico State University, who studied the foxes as a graduate student. Fox carcasses turned up with eyes gouged out and spines ripped away. A year later, fox populations began to freefall. “It became clear that eagle predation was taking a toll on the foxes,” says Roemer. Indeed, the new predator had usurped the fox’s place at the top of the island food chain. Life in paradise had spoiled the foxes. Unlike their nocturnal mainland cousins, the island foxes hunted at all hours of the day. Naïve to the ways of day-hunting golden eagles, the foxes were left vulnerable to aerial attacks. Santa Cruz, which sheltered about 2,000 foxes in 1994, is now home to about 60 wild adults. The subspecies on San Miguel and Santa Rosa, which once numbered 450 and 1,300, respectively, teeter even closer to extinction. Today, not a single wild fox remains on either island. Like the California condor before them, the future of the species now depends on the success of a captive-breeding program. The three islands each boast facilities dedicated to rearing its own species of fox. In the past two years, the captive Santa Rosa Island foxes have given birth to 18 pups. The San Miguel Island foxes have not fared as well; they have only produced seven pups in two years. In spring 2002, the Santa Cruz Island breeding facility’s maiden season, one pair gave birth to five pups. It will be several more years before the San Miguel foxes are ready for release, says National Park Service biologist Tim Coonan, and full recovery of the subspecies may take a decade. The fox recovery program, including the captive breeding and the golden eagle removal, is estimated to cost about $7 million. But before any foxes are released back into the wild, scientists must first mend the other pieces of this shattered ecosystem. That means not only getting rid of golden eagles, but also the feral pigs that drew the birds to the islands in the first place. Golden eagle sightings are rare on Santa Cruz Island these days. Scientists are relocating the birds to the northeastern Sierra, and have removed about 20 eagles from the island so far. Radio telemetry collars fitted on the relocated birds indicate that none have found their way back. But nabbing the last two has proven difficult. The remaining birds probably bred or were themselves born on the islands, and have forged strong bonds to the land, Coonan says. Their presence still poses a huge threat, as the holdouts killed at least eight Santa Cruz foxes in 2001. But the park service is confident they will soon remove the final, stubborn golden eagles from the island. At the same time, scientists are reintroducing bald eagles to the islands in hopes that they will once again guard their territories against golden eagle interlopers. Every summer for the next five years, the Santa Cruz Predatory Bird Research Institute plans to relocate twelve baby bald eagles to Santa Cruz Island. The class of 2002 arrived last summer when they were just a few weeks old—five from the San Francisco Zoo and seven from Alaska. The dark brown birds still hadn’t earned their signature white headdresses, and their wings were too weak to carry them. They spent their first twelve weeks acclimating in the safety of enclosed nest boxes, perched high atop the island cliffs, before they were released to soar into the great blue blur of ocean and sky. The success of the bald eagle reintroduction won’t be clear until this first group of birds starts to breed about five years from now. No one will know for sure whether or not the DDT levels in the environment will be high enough to doom the birds’ breeding efforts until the first eggs are laid. If the eggs are still brittle, humans may have to play midwife to the eagles as they have on Santa Catalina Island. A bald eagle breeding program is underway on that island, but the effects of the nearby DDT dump have lingered. When an eagle lays an egg, a handler removes it and replaces it with an artificial one. The fragile, live egg is hatched in an incubator. Humans raise the hatchling and then release it into the wild. Researchers hope that Santa Cruz is far enough from the DDT dump that the poison will no longer affect the island’s birds. There are many reasons to be optimistic about the bald eagles’ chances. Seabirds such as brown pelicans, cormorants, and gulls are now breeding successfully on many of the Channel Islands, suggesting that DDT levels are low enough that the pesticide doesn’t interfere with bird breeding. And recently, several public agencies settled lawsuits against the Montrose Chemical Company. The $30 million settlement is earmarked for natural resource restoration. Lastly, efforts to cap the DDT spill with tons of clean sediment look promising. Bringing bald eagles back to Santa Cruz Island is just one more component in the attempt to return the ecosystem to a healthy balance. The next step is removing the feral pigs, before they tempt the golden eagles back. Professional hunters have already begun trapping and shooting pigs and goats on the other islands, and will begin their work on Santa Cruz in 2004, a process that could take five or six years. Animal rights advocates dismayed with the project argue that the park service should take a more humane approach to removing the pigs. Nature Conservancy biologist Erik Aschehoug says he welcomes the concern and the funds the “glamour mammal” foxes have drawn to the islands. But, he says, saving the island fox is only a small part of a comprehensive plan to restore the islands to health. Anchored so close to the mainland, the Channel Islands have been exploited by humans for centuries. Now an effort is underway to turn back the clock, and bring a piece of California’s natural history back to life. “We’re on the path to returning to California’s coastal heritage,” says Aschehoug. “The mainland has been developed, farmed, scraped clean. There are very few other places left in Southern California that are reminiscent of California’s rich coastal heritage.” Erika Kelly is a freelance journalist based in San Francisco. |