The population of the fox dropped to an all-time low of just 70 animals on Santa Cruz Island in 2000 before rebounding to 1,300 foxes now, said Yvonne Menard, a spokeswoman for the National Park Service. Santa Cruz is the largest island.
Populations on nearby San Miguel and Santa Rosa islands have also bounced back into the hundreds after dropping in 1999 to just 15 of the cat-sized animals on each island.
The island fox is only found on six of the Channel Islands, a chain of eight islands, five of which form a national park. Each of the six islands has its own unique fox subspecies because of generations of genetic isolation.
In a five-year period in the 1990s, fox populations plummeted more than 90 percent on the rugged and mountainous islands due to an influx of golden eagles, which preyed on them.
The eagles were attracted by hundreds of feral pigs on Santa Cruz Island that also made easy prey and were descendants of pigs brought to the island years ago by ranchers.
The food source allowed the eagles to begin to nest on the island, said Tim Coonan, a biologist with the National Park Service.
Four of the six fox subspecies were listed as federally protected endangered species in 2004, but now biologists say their populations on three of the four islands have recovered almost completely.
"They are doing unexpectedly well," Coonan said in a phone interview Monday after a tour of Santa Cruz Island to publicize the program's success.
"I don't think anyone could imagine that 12 years after the decline was discovered .... we'd be looking at recovered populations."
Alarmed biologists affixed tracking collars to the foxes in the late 1990s after noticing the sharp decline in numbers on Santa Rosa, Santa Cruz and San Miguel islands and Catalina Island to the south.
Results from the three northern islands revealed that the foxes were being eaten by golden eagles.
The decline on Catalina Island was from a disease that had swept through the population and not from eagles, Coonan said.
In 1999, biologists on Santa Cruz Island bred foxes in captivity to boost their numbers. Over the next decade, they released 250 pups back into the wild on the three northern islands, Coonan said.
At the same time, wildlife officials captured and removed 44 golden eagles from the island chain between 2000 and 2006.
They also hired a company to kill 5,000 feral pigs on Santa Cruz in a controversial program to restore balance to the island's ecosystem.
The hunters divided the island into five fenced-off zones and shot pigs from the air to eradicate them.
Now, biologists are working to reintroduce bald eagles to the island instead of the golden eagles that had taken their place.
Bald eagles disappeared from the Channel Islands by the early 1960s due to human impacts, primarily pollution. Millions of pounds of the deadly pesticide DDT and other chemicals were dumped in the ocean off the Palos Verdes Peninsula between the 1940s and 1970s.
The chemicals caused bald eagles to lay thin-shelled eggs that either dehydrate or break in the nest.
More than 40 bald eagles which don't eat foxes now call the northern Channel Islands home and this spring there are at least seven active nests there.
The closed loop of the island ecosystem contributed to the foxes' rapid decline, Coonan said, but it also aided in their quick rebound.
"Once you solve a problem on an island, it pretty much remains solved. No pigs are ever going to come back there," he said.