Developing a sound conservation strategy … depends upon gaining demographic and genetic information for all populations of concern prior to the onset of any irreversible population declines. - Gary Roemer, 1994
Biologist Gary Roemer and his field assistant, Jeff Howarth, were stuck. January 1995 was the wettest month in recorded history at the NRS reserve on Santa Cruz Island, largest of the California Channel Islands. The pair were on the island to do fieldwork for Roemer's UCLA doctoral dissertation on the island fox (Urocyon littoralis). Twice each month for a year, they had journeyed out to Fraser Point at the west end of the island, set up camp in an NRS trailer, and collected data on the social structure and mating behaviors of a fox population that roamed the bluffs above the point.
But once the rain began to fall that January, it didn't stop all month. "There was literally water running off the hillsides," Roemer recalls. Not only was the road to their study site impassable, the road to the boat landing was also underwater. The pair couldn't even get off the island. So they took refuge at the field station and waited. "We passed the time doing data entry," Roemer continues, "reading books from the library, and helping Brian [Guerrero, the reserve steward]."
Roemer was anxious to get back out to Fraser Point. There had been a number of fox mortalities the previous year and he was concerned: "The first mortality was May of '94. Then we lost three to four more from May through December."
Even after the rains eased up, the muddy roads were still impassable for several months into 1995. Finally, Roemer and Howarth decided to hike to their study site. When they arrived in February, they discovered there had been three additional mortalities during their absence. Roemer was sure he knew the cause.
"The forensic information at the kill sites was clear," he explains. "Each animal's pelt had been pierced, some had holes in their skulls, and that requires powerful feet and sharp talons. Also, the limbs were often 'degloved' [the skin pulled back from the flesh], and the sites were often littered with feathers and droppings. There was no doubt in my mind that golden eagles had done the killing."
The big question was, why now? Golden eagles (Aquila chrysaetos) were a mainland species. Though they had occasionally been seen passing over Santa Cruz Island since the late 1800s, they had never been known to nest there or on any of the other Channel Islands. Now the fox kills were occurring so frequently, the birds must have taken up residence on the island. During his two-year study, Roemer lost 21 animals, at least 17 of these confirmed golden eagle kills.
Roemer's discovery triggered a flurry of follow-up research throughout the Channel Islands. Five of the eight islands - San Miguel, Santa Rosa, Santa Barbara, Anacapa, and Santa Cruz - comprise the Channel Islands National Park, and Park Service biologists soon discovered similar dramatic declines of fox populations on San Miguel and Santa Rosa. As the fox's dire situation became clear, The Nature Conservancy (TNC), which owns and protects most of the island, and the National Park Service, which manages it, would launch an unprecedented effort to save the species and restore the damaged Santa Cruz Island ecosystem.
Present-day Santa Cruz Island
A journey out to Fraser Point, at the far west end of Santa Cruz Island, reveals the island's rugged terrain. Even in the best of weather, only the sturdiest four-wheel-drive vehicles can handle the "road" west, which offers gravel- and boulder-filled riverbed alternating with short sections of improved dirt road, open fields, and occasional near-vertical plunges into, and out of, deeply eroded creek beds.
The views along the way are spectacular: to the north, looming out of the haze on the mainland 40 miles away, are the Santa Ynez Mountains; to the south, rugged canyons plunge toward the ocean, their flanks still scarred from decades of overgrazing by sheep. "There are still places down there I've never seen," observes the reserve's director, Lyndal Laughrin. Quite a statement, considering he's been working on Santa Cruz Island and running its field station for over 30 years.
Fraser Point itself feels almost as much a part of the ocean as of the land - waves pounding on the unprotected coast, cold windy fogs blanketing the bluffs.
"This was one of the two study sites Gary [Roemer] had set up." Laughrin gestures to the open bluffs above the point. "He had a grid here and another one in the central valley to compare the populations at the two different sites." The foxes have been the focus of basic research on the island since the field station was established in 1965. Lyndal himself wrote his dissertation on them in the 1970s, before shifting his focus to restoration ecology. Three other UC graduate students had also done theses on different aspects of the animals' behavior and social organization. None of these earlier works noted any major declines in their population.
"Back in the eighties, there was a major effort to remove sheep from the island," Laughrin recalls. "Overgrazing had really devastated many of the hillsides. We thought with the sheep gone, the island foxes would do great."
But ecological matters didn't play out the way everyone had envisioned. Over the next ten years, the fox population on Santa Cruz Island dropped more than 90 percent, from 1,300 individuals in 1994, to 133 animals in 1999, to between 70 and 80 today. That translates, roughly, as one less fox every other day. But what could have caused this dramatic shift?
Apparent competition
Roemer, whose UCLA graduate research was partially funded by two NRS Mathias grants, is now a professor at New Mexico State University, Las Cruces. In a recent phone interview, he recalled the breakthrough. "The first golden eagle I saw on Santa Cruz I flushed off a piglet it had killed," he says. "Later, it hit me that the eagle had two prey. There's a concept called 'apparent competition' that was developed in the 1970s. It states that when two prey species share a predator, one of the species may be well adapted to high predation pressure, while the other species may be more vulnerable."
In this instance, the two prey species were island foxes and feral pigs, the latter descendants of domestic stock brought to the island in the 1850s. The two species didn't compete directly, but, as golden eagle prey, the fox was at a disadvantage. It reproduced quite slowly (one litter of one to five kits per year) and even the cat-sized adults were small enough to be prey. Feral pigs (Sus scrofa), on the other hand, could have large, multiple litters each year, and adults quickly became too big to serve as eagle prey.
Interestingly, one major winner of this ecological shift was a true island fox competitor. The island spotted skunk (Spilogale gracilis amphiala) population soared as the fox population declined. When Laughrin conducted his studies in the 1970s, he rarely captured a skunk in his fox traps. Today researchers capture more skunks than foxes.
Feral pigs may have initially attracted golden eagles to the islands, but the foxes turned out to be the easier prey. Stable isotope studies conducted on various Santa Cruz Island samples, including eagle breast feathers, revealed that the golden eagle diet consisted of 51 percent fox, 34 percent piglet, and 15 percent skunk.
Roemer realized immediately that the fox population on Santa Cruz Island was in great peril. In collaborating with researchers doing work on other Channel Islands, it soon became apparent that the same pattern was repeating itself in those locations as well. On San Miguel Island, the number of island foxes was found to be dropping dramatically -from 450 to 40 in four years. By 2001, only 15 foxes survived there.
The rescue plan
Fast forward to 2002. The current status of the island fox on Santa Cruz Island comes clear on a high ridge overlooking China Harbor. A series of six large chain-link pens - four walls and a roof - have been scattered along the ridge as part of a captive breeding program begun earlier this year. Inside each pen, hidden among large branches, is a pair of foxes. The animals aren't shy; when humans approach, they peer curiously from their den to see if it's time to eat. One of the pens holds five kits, a single large litter that represents the only successful mating so far at the Santa Cruz Island facility. With 17 foxes here, and 50 to 60 still in the wild, the population is on the verge of extinction.
On the next ridge is another nursery: a tall fledging tower that provides a panoramic vista for four bald eagle chicks. Bald eagles (Haliaeetus leucocephalus) once played a key role in the Santa Cruz Island ecosystem population and, because they fed almost exclusively on fish and carrion washed up on the beaches, they posed no threat to the foxes. In fact, many scientists believe the presence of bald eagles protected the island from encroaching golden eagles. But the once-common bald eagles disappeared from the Channel Islands in the 1950s, a decline believed to be the result of agricultural pesticides, primarily the insecticide DDT, dumped off the coast of Los Angeles into the ocean near Santa Catalina Island, about 75 miles southeast of Santa Cruz Island. The four bald eaglets on this fledging tower were hatched at the San Francisco Zoo from eggs taken on Santa Catalina. They were brought to the site to re-establish the Santa Cruz Island population. More chicks will be brought in over the next four years, 12 per year for a total of 60.
Elsewhere, predatory bird specialists are working hard to capture and remove the last three golden eagles nesting on the island. Since November 1999, 22 golden eagles (12 adults, 7 subadults, 3 chicks) have been captured and removed. The adults were radio-tagged and taken to the far northeast corner of the state. So far, none has returned to southern California. Each capture, however, has become more difficult.
"I knew it would get harder," says Brian Latta of the Predatory Bird Research Group at UC Santa Cruz, "but I didn't know it would get this hard. These birds are very smart and very cryptic. We have to constantly develop new capture techniques, because they won't fall for the same trick twice." The latest strategy - chasing the birds to exhaustion with a helicopter and then netting them when they land - has proven difficult on the island's rugged terrain. The first week of work produced no new captures.
Meanwhile, thousands of feral pigs continue to roam the 96-square-mile island, and extracting them from the remote canyons will be extremely time-consuming. Under a Nature Conservancy effort beginning this fall, fences will be built that divide the island into six sections. The plan is that each year the pigs will be removed from one section until they're all gone.
Future lessons
Island ecosystems have been crucial in the development of evolutionary theory. Beginning with Darwin's work on Galapagos finches, the rapid divergence of island species has fueled the fires of scientific debate on how life evolves. Islands have also served as major test cases for conservation strategies, because small population sizes and lack of genetic variation put island species at risk. Birds provide a good example of this. Fewer than 20 percent of all bird species are restricted to islands, but more than 90 percent of extinctions of bird species in historic times have occurred on islands, and 39 percent of all threatened bird species are island species.
Santa Cruz Island will be an important conservation story, because restoring a native ecosystem is like trying to put Humpty Dumpty back together again. All of the pieces must fit into place - the pigs and golden eagles successfully removed, the bald eagles reintroduced, and the island foxes restored - to reconstruct a species assemblage long since lost.
As animal populations throughout the world become fewer in numbers and more fragmented, the chances of entire food chains suddenly collapsing become greater. This is why it is crucial we do basic research on the animals that survive today to acquire an understanding of a species before it reaches a crisis.
It has taken eight years for us to assess and respond to the plight of the island fox. During that time, their situation has become much more desperate. Roemer observes: "The government has to be able to respond to scientific input much more quickly, in six months rather than four to five years. We also need to facilitate basic research before we get to a crisis like we have today. Without a basic understanding of how the system functions, we will be unable to institute any mitigating actions." - JB
For more information, contact:
Lyndal Laughrin, Reserve Director
Marine Science Institute
Trailer 342
University of California
Santa Barbara, CA 93106
Phone: 805-967-2224
Email: laughrin@lifesci.ucsb.edu |
