The island fox, listed in 2004 as a federally endangered species, is approaching biological recovery on Santa Cruz and San Miguel Islands within Channel Islands National Park.
Four of the six subspecies of island fox declined by over 90% in the late 1990s. The cause of the decline on the northern Channel Islands was predation by golden eagles. Since 1999 a total of 44 golden eagles have been live-captured and relocated to the mainland. Today, with over 1,700 foxes in the wild, the island fox population is on the road to recovery.
The fox population of about 320 animals on San Miguel Island has increased from only 15 animals in 1999 when all animals were brought into captivity as a measure to save the species. Today survivorship of island foxes on San Miguel Island is 94%, an above-normal level.
Santa Cruz Island, the largest and most diverse Channel Island, boasts of a fox population of over 1,000 with an annual survival rate of about 96%. For context, this fox population has increased from a low of less than 70 foxes in 2000.
On nearby Santa Rosa Island recovery is slower with the population of 390 animals still exposed to golden eagle predation. This past spring 11 radio-collared foxes died from eagle predation. Golden eagle feathers were found at two fox mortality sites and several sightings of golden eagles occurred in the same time period. Consequently, annual fox survival dipped from near 90% at the beginning of 2009 to 61% presently.
Subsequently, in May two island foxes succumbed to eagle predation on the west end of Santa Cruz Island following sightings of golden eagles in the area. These are the first fox kills in association with golden eagle sightings in over a year on this island. “The rapid recovery of island foxes may be one of the most successful recoveries of an endangered species to date,” said Dr. Lotus Vermeer, Director of The Nature Conservancy’s Santa Cruz Island Preserve.
“We measure fox recovery by looking at the overall populations and are excited by the progress we are seeing,” said Russell Galipeau, Superintendent of Channel Islands National Park. “The continued predation by golden eagles is unfortunate and is being monitored closely.”
An unusual incident occurred in late May in the bald eagle nest at Pelican Harbor on Santa Cruz Island when bald eagle webcam viewers observed one of the adults bringing an island fox carcass into the nest. It is not known whether the adult bald eagles preyed upon this fox or whether they recovered a dead fox carcass. Bald eagles are known to primarily feed on fish, seabirds, and marine mammal carcasses and it is not their natural tendency to prey on terrestrial mammals.
Next week a group of approximately 60 biologists and managers from various agencies and organizations will convene for an annual meeting in Ventura to discuss island fox recovery. They will present the current status of island fox populations on each of the six Channel Islands that supports this endemic species and will identify measures for continued island fox monitoring, research, and protection.