Genetically, the island fox on San Miguel Island is most closely related to foxes on Santa Rosa. Monitoring of the fox population on San Miguel between 1994 and 1998 indicated a dramatic decrease. In 1994 the National Park Service estimated the population at 450 animals. By 1998 the population estimate was only 40 animals. Efforts to determine the cause of the decline included examining the potential effects of disease, a decline in food supply, and the effects of predators. In 1998, the Institute convened a panel of wildlife disease specialists and wildlife biologists in Davis, California, to review fox data from the National Park Service and the Institute. At the time there was no conclusive evidence that disease had played a role in the decline of the fox populations on the Northern Channel Islands. In late 1998, telemetry transmitters were placed on a few of the remaining foxes on San Miguel to closely examine mortality factors. From this study it was determined that predation by golden eagles was a significant factor in the decline of the foxes. The Channel Islands National Park has organized an island fox Recovery Team to help develop a strategy for understanding the decline, develop protocols for conserving the remaining foxes, and to formulate conservation techniques such as captive breeding and reintroduction to help the populations recover. The Institute has two biologists on the Recovery Team, who assist the Park in their efforts to conserve this unique species
Captive Breeding Program
In 1999, the Channel Islands National Park instituted a captive breeding program to protect the remaining island foxes on San Miguel Island from golden eagles and to produce foxes for eventual release back into the wild. A total of 11 pens have been constructed: Eight 500-ft2 pens placed in a U-shaped configuration (each pen has an interior door that splits the pen in two); One 300-ft2, L-shaped pen; and two 200-ft2 pens. All pens were constructed from 1.5-inch chain-link fencing and contain a 2 ft ground skirt partially buried to prevent animals from digging out. Various structures were placed inside the pens to provide suitable denning and resting sites for the foxes. A video monitoring system was installed to monitor the behavior of the caged foxes. During the first year, 14 wild foxes (4 males: 10 females) were brought into captivity and placed in the 11 breeding pens. Only one other fox is known to reside on the island outside of the cage compound. One of the four captive pairs produced a litter of two pups (1 male:1 female) in 2000; This was the first natural mating and successful rearing of island foxes in captivity. Both pups survived and the male pup was subsequently paired with an adult female in the fall of 2000. The golden eagle predation issue is currently being mitigated (see Santa Cruz Island), so threats to released foxes should be considerably reduced.