Endangered island fox population rebounds
By Chuck Graham 11/13/2008
Wide-eyed and bewildered, a tiny, house cat-sized island fox was reluctant to flee from its cage for the first time into the wilds on windswept Santa Rosa Island. The captive-bred predator remained in its cage for several minutes, sniffing the outside world it would soon claim as its own, bringing an end to 10 years of captive breeding at the Channel Islands National Park.
The captive-bred programs on neighboring Santa Cruz Island to the southeast and San Miguel Island to the west were shut down in 2007, their wild populations rebounding rapidly from near extinction. Their recovery appears to be one of the swiftest recoveries of an endangered species in the history of the Endangered Species Act.
“It’s a great time to think about island foxes,” said Tim Coonan, terrestrial biologist for the Channel Islands National Park. “Things are going so well in the wild, we can close down captive breeding completely this year.”
This was due to two factors, the first of which was the ability of the species to do well in the wild when its primary mortality factor (predation by golden eagles) was removed. The cooperative recovery effort, which began more than five years before the island fox was officially listed as endangered, ensured that recovery techniques such as captive breeding and releasing and golden eagle removal, were implemented quickly and professionally. The return of bald eagles, absent on the archipelago for more than 50 years, and the eradication of approximately 5,000 feral pigs from Santa Cruz Island that officially ended in the spring of 2008, also weighed heavily in the recovery of the island fox and the return of a natural ecological balance to the chain.
Since the removal of more than 40 golden eagles, the island fox survival rate has risen to 90 percent on all three islands.
Why captive breeding was slow on Santa Rosa appears to be a mystery.
Like San Miguel, the wild population had plummeted to critical in 1999-2000, each island down to just 15 animals. However, San Miguel foxes rebounded more quickly going from a peak of 400 animals down to 15 and back up to 130 foxes in the wild today. Santa Rosa is a larger island and had a density of 1,000 foxes before golden eagles arrived in the 1990s. After dropping to 15 animals, there are currently 110 in the wild. Historically, Santa Cruz had approximately 1,500 island foxes.
That number dropped to a low of 70. Today there are 410 on the largest of the Channel Islands.
“We thought it was the captive facilities, their location, or we didn’t pick pairs as well,” explained Kate Faulkner, chief of natural resources for the park, “because we were choosing who would mate with who, and sometimes they didn’t get along.”
The numbers were so low on San Miguel and Santa Rosa that genetics became an issue to avoid inbreeding, so matching compatible pairs was a priority. Island foxes are monogamous and mate for life.
“We really didn’t know what the answer was,” continued Faulkner. “We had vets, zoo people trying to help us improve the situation. In the end, it was clear the foxes were doing better in the wild.”
Faulkner said the U.S. Fish and Wildlife Service were notified of their plans to release the remaining foxes and close down captive breeding.
For now, the species will remain listed as endangered.
The rest of the captive population on Santa Rosa will be released in November, preferably in regions of the island void of island foxes.
It’s tough on newcomers when established foxes have already marked their territories.
“When they’re first released, they have to work out those territories,” said Faulkner. “It’s easier releasing foxes on islands when densities are really low. It gives foxes a place to go. That was a problem on Santa Cruz, releasing into an environment that had a lot more foxes, so newly released foxes were getting beaten up by more established foxes.”
E-mail Chuck Graham at firstname.lastname@example.org