Rare Island Foxes Dying; Scientists Mystified
Channel Islands National Park biologist Tim Coonan has a mystery to solve.
Clues are scarce, and time is of the essence.
At stake is the life of the island fox--a subspecies of the mainland gray fox found on the Channel Islands and nowhere else in the world.
Four years ago more than 450 of the little foxes bounded through the coyote brush on the wind-swept plateaus of San Miguel Island.
Today their numbers have plummeted to 40.
No one knows why.
The decline of the island fox population puzzles rangers and biologists.
Golden eagles have picked off foxes on some of the other Channel Islands. But there are no golden eagles on San Miguel.
Depletion of habitat due to development, or lack of food can cause such a decline. But the mouse population the foxes feed upon has not changed.
Stranger yet, for several years the fox populations declined on San Miguel, but remained stable on two other islands in Channel Islands National Park. But this year populations fell sharply on the other islands, too.
“That was a shock,” said Tim Coonan, a terrestrial biologist for the park. “This year we are coming to grips with the fact that they are disappearing on Santa Cruz and Santa Rosa as well . . . . It’s a real conundrum.”
But now, armed with a $50,000 environmental grant from Canon U.S.A., the National Park Service will begin tests on the tiny island foxes to try to find out what is killing them off.
The grant money will be used to take additional blood samples and perform necropsies in an attempt to determine if disease is decimating the island fox population.
Often swathed in clouds and fog, San Miguel is the most isolated and least accessible of all the islands in the park.
Fox Has Thrived on San Miguel
Although the foxes live on three of the islands in the park, as well as two islands farther south, it is San Miguel where the island fox has thrived.
Coonan flew there recently to check traps. He walked over the dry grasses. There, in a 2 1/2-foot-by-8-inch trap, was a pup--lured into the metal box by cat food.
Coonan pulled out the frightened pup. The fox, smaller than a Yorkshire terrier, darted its dark eyes about nervously. Then the biologist grasped it by the chin and scratched it behind its cinnamon buff ears.
Biologists believe the island foxes rafted out to the islands more than 20,000 years ago. Over the millenniums, the foxes on the different islands have gradually become distinct--both from the mainland gray fox and from each other.
Like many island mammals, they are smaller than their mainland cousins, in this case, by about 18%. But they are the mega-fauna of the island ecosystems--larger than any other species except the spotted skunk.
Artifacts from Chumash graves reveal that on some islands the foxes were domesticated and kept as pets. At death they were buried with their masters.
Since they arrived thousands of years ago the San Miguel foxes had survived overgrazing, drought and massive soil stripping.
But in the 1980s, the population plunged to a level so low that the state listed them as endangered. In 1993, the park service began a basic monitoring program for all terrestrial island creatures.
They inserted tags the size of a grain of rice between the foxes’ shoulder blades with needles. These can later be read like a bar code at the supermarket to keep track of individual foxes.
By 1994, the fox population on San Miguel was higher than it had been in years--450--but the very next year the population dropped to 300. It has continued to drop every year since. There were 100 foxes in 1996, only 70 last year and just 40 this year.
“The early part of the decline we kept waiting for them to bounce back,” Coonan said. But they didn’t. And officials were growing alarmed.
“It’s a crisis time. This year’s numbers are even more disturbing. . . . It’s unlikely that a population with that few animals could make it if struck by disease,” Coonan said.
Preliminary testing of the foxes’ blood and feces revealed some cases of canine ideno virus--which can cause hepatitis--and heartworm. The virus hits pups hardest--and could explain why they are not surviving from year to year; heartworm cuts life expectancy and could explain the lack of geriatric foxes.
Biologists do not know how the diseases could have reached the distant island, 55 miles off the Ventura coast.
They doubt that mosquitoes, which carry some viruses, could have flown the channel. But in wetter years, like 1995, the mosquito population on the island increases.
Dogs May Carry Diseases to Island
Biologists also wonder whether sailboat owners mooring at the
island’s sandy beaches are letting their dogs roam free in the isolated island environment--introducing new diseases, like heartworm, to which the fragile fox population has built no immunity.
But Coonan said evidence of the two diseases does not mean they are responsible for the decline. Foxes on islands farther south, for example, also have heartworm, but they are surviving. Still, the San Miguel subspecies could have lower resistance.
Although rangers have not spotted any golden eagles over San Miguel, they cannot rule out the aerial predators either. Fox carcasses on Santa Cruz and Santa Rosa show evidence of bird kill.
“They probably haven’t seen an eagle before so they are very vulnerable,” Coonan said. “They haven’t looked to the skies . . . . They haven’t had to.”
At this point, park biologists believe disease is the problem. But more research is needed.
“We don’t have the smoking gun yet,” Coonan said. “That’s why I would really like to look at some of the carcasses.”
Despite the sharp decline in the population, biologists failed to draw any money through normal park service channels.
Lab testing of the blood and carcasses, as well as the frequent flights to the island cost money the park service simply did not have, they said.
That is when Canon stepped in and provided an environmental grant as part of a $3.5-million program to preserve and conserve animals. None of that money can be used for facilities. This year, Canon awarded $50,000 grants to 17 national parks.
“We had the clues, but no answers,” said Carol Spears, chief of interpretation for the Channel Islands National Park. “Without the grant we could not have continued to do the kind of research we needed to.”
Keith Paglen, the head of Canon’s Clean Earth Campaign, said the grants reap dividends for his company in the marketplace.
He also hopes that Canon’s environmental efforts will be an example to others in the industry.
Park officials say the grant money will be used to do research through this fall.
“Hopefully we identify the cause of decline this year,” Coonan said. “Then we can start treating them next year.”
With that, Coonan released the fox pup and it ran off like a cat, its fur camouflaging it perfectly in the tall island grasses.