Not long ago, foxes native to the Channel Islands off the California coast teetered on the edge of extinction.
They have rebounded to the point where U.S. wildlife officials on Thursday removed three subspecies of island fox from the roster of federally endangered species, hailing their comeback as the fastest recovery of any mammal listed under the Endangered Species Act.
The diminutive foxes that roam San Miguel, Santa Rosa and Santa Cruz islands were placed on the endangered list in 2004 after their populations were nearly wiped out by golden eagles.
Scientists credited the swift recovery to an effort to relocate predators and breed foxes in captivity so they can be reintroduced to the wild.
"We're ecstatic that we've reached this point so quickly," said Steve Henry, field supervisor of the U.S. Fish and Wildlife Service's office in Ventura.
About the size of a house cat, the island foxes—with their gray coats and reddish-brown ears—are only found on six of the eight Channel Islands where they have lived for thousands of years.
Populations have returned to self-sustaining levels ranging from an estimated 700 foxes on San Miguel Island to 2,100 foxes on Santa Cruz Island.
Centuries ago, ranchers and farmers imported nonnative animals such as pigs, cattle and sheep to the islands. Golden eagles migrated after native, fish-eating bald eagles were wiped out by the discharge of chemical DDT off the coast.
The golden eagles preyed on piglets and hunted foxes. By 2000, there were only 15 foxes each on San Miguel and Santa Rosa islands and 55 foxes on Santa Cruz Island.
The wildlife service partnered with the National Park Service, Nature Conservancy and Catalina Island Conservancy to hatch an aggressive plan that included moving golden eagles to Northern California, reintroducing bald eagles to the islands, vaccinating foxes and breeding them in captivity.
The effort was not without controversy. Thousands of pigs were shot and killed, angering animal rights groups. Wildlife officials said eliminating pigs was necessary to force golden eagles to forage elsewhere and help the foxes bounce back.
The islands' remoteness also played a key role in the foxes' resurgence, giving scientists better control over recovery efforts than if they happened on the mainland.
Years ago, "you would not have seen a fox. Now, you go out there and you don't have to wait very long before a fox crosses your path," said Scott Morrison of the Nature Conservancy, which co-owns Santa Cruz Island.
Funding for the yearslong recovery came from public and private sources and included volunteer time. Officials did not have an estimate of the overall cost but said the captive rearing and monitoring portions of the program cost about $20 million.
With the fox delisting, 19 animals and plants have been pulled from the endangered species list since President Barack Obama took office, more than previous administrations, wildlife service director Dan Ashe said.
The last U.S. mammal to be removed from the list in record time was the eastern Steller sea lion in 2013 after more than two decades. Since the Endangered Species Act passed in 1973, 37 species have recovered.
Biologists planned to monitor foxes on the northern Channel Islands by conducting periodic health checks and tagging select foxes with radio collars. Technician Stacy Baker used a tool Thursday to examine the teeth of a 3-year-old female fox on Santa Cruz Island. After giving it a clean bill of health, the fox scampered into the underbrush.
Foxes on Santa Catalina Island—a tourist destination—also are recovering but not as fast as their counterparts on the northern Channel Islands. Their numbers plummeted in the 1990s after an outbreak of canine distemper, likely brought over from the mainland.
Federal officials downgraded the status of the Catalina foxes from endangered to threatened because disease outbreak remains a concern.
Explore further: Feds: Remove 3 California foxes from endangered species list