Land of the Vanishing Foxes - helping the San Miguel Island foxes survive

Animals, Jan, 2000 by Deborah Knight

Keith Rutz kneels on the dry grass amidst an austere, treeless landscape and sets out an array of silver bowls. Into each he measures a few scoops of high-grade kibble, sprinkles on some raisins, and chops half a hard-boiled egg on top. The meal resembles an odd Caesar salad.

"Hi, girl," he says quietly as he enters the first cage. No animal is visible, just a plywood den and a tangled bush. He leaves the bowl covered with a board and a rock to keep out mice. It is twilight, and a bright half-moon shines down on a small metropolis of wire pens. Eleven pens, 12 captive foxes, and two field staff on a remote, fog-shrouded island: the fate of the San Miguel Island fox hangs on these tiny numbers.

The island fox inhabits only one place in the world, the Channel Islands off the coast of southern California. Like many isolated species, the island fox has evolved some endearing characteristics. Separated for thousands of years from its mainland counterpart, the gray fox, it has become diminutive, about the size of a house cat. Not having to contend with predators, it is more diurnal and quite tame.

Foxes live on six of the Channel Islands and have evolved on each into a genetically and physically distinct subspecies. In 1993 the National Park Service began a survey of foxes on three northern islands out of the five that lie within the Channel Islands National Park. The number of foxes rose the first year and then began a drastic and mysterious decline. Here on San Miguel, the smallest of the islands, the population plummeted over four years from an estimated 400 animals to about 20. Without emergency measures, extinction of the San Miguel fox seemed certain.

Now Rutz is part of a team that carefully tends these rare captives. In the next cage, a Fox stares warily. It has a delicate face with pointed nose and ears and slanted, squinting eyes. As Rutz approaches, it skitters away catlike, curls up in a far corner, and buries its nose in its bushy tail. The animal's coat radiates a canid elegance: the ears, neck, underbelly, and tail are rich red, and its gray back is flecked with silver-tipped guard hairs.

In another cage two foxes crouch together, one of two pairs here that were radio-tracked together in the wild. Island foxes form a bond for life, and the males help rear the pups, though genetic tests have shown that 25 percent of pups are not in fact related to the male in the pair. To make sure these two got along, they were placed at first in adjacent pens. The foxes aren't thought to dig much--they live in dens under bushes or rock overhangs. Still, to prevent escape, wire mesh is buried around the inside of the pens. Rutz purposely left a patch of earth between these pens free of mesh, and the first night the male dug under and joined his mate.

The foxes of San Miguel are being trapped and held here for a captive-breeding program and eventual release back into the wild. But they are here for another reason as well. Initially, scientists suspected that an introduced parasite or disease was causing the foxes' demise, the kind of problem that often devastates island populations. But no such culprit was found. Then a new suspect emerged, one that required putting the foxes in protective custody.

Rutz arrived in the fall of 1998 as a biological technician, the Park Service's title for those who do much of the less glamorous work with wildlife. To figure out what was killing the foxes, he trapped them, put radio collars on them, and released them. Each night he would tromp across the island with a handheld antenna, following individual animals. The collars emit a steady 55-beat-per-minute signal, like a heartbeat on a monitor. If the transmitter doesn't move in six hours, it shifts to double time--the mortality signal. Rutz began collaring in mid-October 1998. The first week in November, he heard his first mortality signal.

The remains of the fox had talon holes in the skull. The sternum had been split open, the innards eaten, the legs pulled inside out, and the bones picked clean, ribs snapped off at the spine. The pattern was classic raptor.

Golden eagles were known to take foxes on one of the other islands but had never been seen at San Miguel. Nevertheless, in the coming months there were five more mortality signals, and three of the remains fit the pattern of raptor predation. Near the time of each death, a golden eagle was seen in the area.

That the paths of the golden eagle and the island fox should meet at this juncture is only one chapter in a long history of ecological upheavals brought on by humans. The story has been pieced together by Gary Roemer, a researcher with the Institute for Wildlife Studies who has been studying the foxes since 1988. One factor is the eagles' access to lots of meal-sized piglets. Before the islands became a national park in 1980, they had long been used for ranching, and on one nearby island feral pigs still run rampant. Also, golden eagles on the mainland were flourishing. Once targeted regularly by ranchers, the mainland population is now so healthy that immature birds must strike out to new areas to find territories.