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.