Imperiled foxes on Santa Cruz Island will likely go extinct unless the National Park Service removes golden eagles, a protected species, through bold means, perhaps even shooting them, a new study concludes.
Such a draconian step may be necessary because the eagles have eaten so many of the diminutive foxes that the animals are spiraling toward extinction, three experts write in an article appearing today in the journal Science.
The article crystallizes some of the stark ethical questions that face society as greater numbers of rare animals and plants worldwide compete for survival.
“Conservation of species threatened with imminent extinction may require drastic measures that can be emotionally charged, politically unsavory and legally challenging,” the biologists wrote.
The eagles also threaten fox subspecies on two neighboring islands -- Santa Rosa and San Miguel -- where attempts are underway to save the foxes from extinction, said one of the paper’s authors, UC Davis conservation biologist Rosie Woodroffe.
Park Service officials said this week that they have not determined that golden eagles must be destroyed, and that any such decision would require considerable study. Making the task even more difficult, the three fox subspecies are candidates for protection under the Endangered Species Act while the golden eagle is protected by two other federal acts.
The three fox subspecies exist nowhere else in the world. Each island has seen its population of foxes plummet precipitously since the eagles -- for reasons not entirely clear -- began colonizing them in the early 1990s.
On Santa Cruz Island, the fox population dropped from about 1,500 to fewer than 100 in less than a decade. So few foxes remained in the wild on Santa Rosa and San Miguel islands that biologists decided to bring them into captivity in hopes of saving them.
Breeding programs are underway on all three islands and, just two weeks ago, a handful of foxes were released on Santa Cruz and Santa Rosa.
The foxes are biologically distinct from the rare foxes on Santa Catalina Island, where 10 captive-bred animals were released into the wild Tuesday. To date, golden eagles have not settled on Catalina or preyed on the foxes there.
Santa Rosa, San Miguel and part of Santa Cruz Island are part of Channel Islands National Park, where park scientists have been struggling to restore native animals and vegetation by removing nonnative species. Since 1999, biologists working for the park have relocated 31 golden eagles to northeastern California.
An estimated eight eagles, however, have eluded capture by biologists tracking them on foot and with helicopters.
Three-quarters of Santa Cruz Island is owned by the Nature Conservancy, which is working with the Park Service to preserve native species. Starting next spring, they plan to remove an estimated 1,000 nonnative feral pigs that have damaged island vegetation.
Such a step is strongly supported by island biologists. The new study, however, warns of “a potentially disastrous effect of removing pigs while eagles remain.” The eagles, deprived of piglets as food, could begin preying on foxes even more vigorously, the scientists say.
The three authors reached their conclusions after creating a model to test how the Santa Cruz Island fox has fared under various levels of eagle and pig control.
Park managers hope that captive breeding of foxes on all three islands will increase their populations.
Some biologists oppose releasing any foxes, saying the risk from eagles is too great.
“It doesn’t make sound sense from a conservation perspective,” said Gary Roemer of New Mexico State University, a co-author of the Science article.
Park officials, however, say they cannot keep the foxes caged indefinitely. They plan to keep close watch on newly released foxes, tracking them with radio collars. If eagles begin preying on them significantly, the foxes could be recaptured for protection.
“We don’t take these releases lightly,” said Channel Islands Park Supt. Russell Galipeau. But unless there are foxes in the wild, experts cannot determine if they can co-exist with a small number of eagles.
“I feel that as a manager, I’ve got to know that before I can go to the alternative,” Galipeau said. He said officials will review the issue in six months, when they know more about the success of relocating the birds. The Nature Conservancy is taking a similar approach.
In an ideal world, scientists could conduct controlled studies using animals that are not endangered to better understand exactly why the fox population declined and how to reverse it.
“If we had some island where it was jackrabbits, and we could do a controlled study, we would,” said Brian Latta, a field scientist with the Predatory Bird Research Group at UC Santa Cruz, which is trapping and moving the eagles.
But so few foxes exist that just one or two eagles could affect their survival. So could the timing of the pig removal.
“It’s an indication of how fragile the balances are -- one little piece of the puzzle, you take it out and it has these cascading effects,” Latta said.
Such problems demonstrate the precarious condition of wildlife on islands where human influences -- whether farming, grazing or DDT use -- have disrupted the natural order.
Because of the unique nature of islands, Channel Islands National Park is brimming with unusual wildlife. Seventy of its plant and animal species exist nowhere else.
Islands are especially vulnerable to extinction: The park contains 35 plants and animals that are protected by the federal Endangered Species Act or are candidates for such protection.
Such a delicate balance is easily upset by humans.
One example is the golden eagle, native to the mainland but not to the islands. Some biologists studying the recent appearance of island eagles -- and the foxes’ rapid decline -- believe it may be linked to DDT deposits off the coast that devastated the bald eagle population in the 1950s and ‘60s.
Bald eagles -- the national symbol -- are native to the islands, but when their numbers declined, one theory goes, it opened up the territory for golden eagles, which were rebounding on the mainland and looking for new nesting sites.
The Park Service has begun releasing young bald eagles on the islands, but their numbers remain small. Bald eagles tend to prefer fish, while golden eagles often hunt jackrabbits -- prey about the size and weight of an island fox.
One park expert cautions against viewing the dilemma as foxes versus eagles.
“It’s more interesting and more complicated than that,” said Peter Dratch, endangered species program manager for the National Park Service. For instance, the removal of pigs is part of a restoration process that affects all endangered species on the island.
Dratch said he is not aware of any other national park facing the quandary of having to use lethal means to remove one protected species to save another. Before any such decision, the U.S. Fish and Wildlife Service would be required to conduct extensive environmental reviews and other time-consuming studies.
Such a choice is laden with scientific, legal and ethical implications, some experts said when told about the situation on the islands.
“This is a sad situation, the sort of thing that’s being exacerbated by our insane growth mania,” said Paul Ehrlich, a biologist and the Bing professor of population studies at Stanford University. He said he would not object if a few eagles were sacrificed, but he added, “It depends on quite difficult value judgments about the value of the foxes.”
Such judgments will become more common with increased extinction rates, said David S. Wilcove, a professor of ecology and evolutionary biology at Princeton University.
“Unfortunately, in a world where humans have an increasingly large footprint, where natural areas are shrinking in size or are being altered by alien species, we’re going to have to make more hard choices,” he said.
“We’re essentially remaking the world.”