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February 16, 2016

UPDATE!  NEWS FLASH!  Representing the fastest successful recovery for any Endangered Species Act -listed mammal in the United States, the U.S. Fish and Wildlife Service on August 11 announced the final de-listing of three subspecies of island fox native to California’s Channel Islands. For more see,

By Eric Miller, DVM, Dipl. ACAM
Senior Vice President, Zoological Operations

When Saint Louis Zoo Research Director Dr. Cheryl Asa was enlisted more than 15 years ago to help turn around the crashing numbers of rare foxes on the Channel Islands off the California coast, she could not have known that the little foxes were to be the focus of a rare success story of saving animals from extinction.

Federal wildlife officials recommended on Feb. 12 that three fox subspecies native to California's Channel Islands be removed from the endangered species list, saying their populations have made an historic recovery. The U.S. Fish and Wildlife Service leadership is calling their resurgence the fastest successful recovery of any mammal listed under the Endangered Species Act.

Four fox subspecies that live on San Miguel, Santa Rosa, Santa Cruz and Santa Catalina islands were placed on the endangered species list in 2004. Disease and predators had dramatically reduced their numbers.

This was a typical case of unintended consequences—settlers on the island bred pigs and sheep. When they left the islands, some of the pigs eluded capture and had piglets. The piglets attracted golden eagles and were perfect food for their chicks. But as the piglets grew to be too big, eagles began devouring the foxes instead. The golden eagles felt free to show up because the now-banned chemical DDT had wiped out their competition: the fish-eating bald eagle.

By 2000, National Park Service staff had found and captured only 15 of these lovely foxes on San Miguel Island.

Despite the odds, wildlife officials and geneticists, population  biologists and veterinarians from several U.S. zoos went into action, crafting a plan that include:

  • Relocating the non-native golden eagles from the northern Channel Islands;
  • Killing off Santa Cruz's huge population of feral pigs;
  • Reintroducing bald eagles;
  • Vaccinating the foxes in Santa Catalina against canine distemper (brought to the islands by the dogs of tourists); and
  • Breeding the foxes in captivity. This breeding initiative was critical to have a number of foxes to reintroduce. It was the reintroduction effort that led to the population growth of this species.

For this complex breeding initiative, the National Park Service, which oversees the islands, called in Cheri Asa, Ph.D. She is one of the world’s leading carnivore reproduction experts, and for accredited zoos, she directs the AZA Reproductive Management Center at the Saint Louis Zoo.

 These foxes had never before been raised in captivity, so Dr. Asa was charged with conducting a number of studies to jump-start a captive breeding program.

A Saint Louis Zoo endocrinologist did hormone studies from the feces of the captive foxes to determine that they were induced ovulators—meaning they ovulated only from externally derived stimulus during, or just prior, to mating, rather than cyclically.

Dr. Asa conducted a sperm viability study and camera-based pen studies, investigating behavior and male aggression.  She exhaustively studied the factors that affected reproduction success.   

All of the efforts that the team established brought on this recovery, but it took time.

As of last year, there were 520 native foxes on San Miguel and 874 on Santa Rosa. The number of foxes on Santa Cruz Island had risen to 1,750 and the number of foxes on Santa Catalina, where distemper reduced the population to 103, had jumped to 1,717.

With these numbers, Dr. Asa agreed the island fox story is “a great one—one of the few success stories in conservation.”  She credited this success to Tim Coonan, National Park Service ecologist who for 23 years has led this recovery. “Tim deserves most of the credit.  He was amazing to work with,” she said.

Coonan returned the compliment, “That Channel Island foxes have recovered to this point is due in no small part to Cheri Asa’s efforts to establish and improve captive breeding methods for this species.”   

While congratulations are due all around, we can’t forget that nearly 1,200 bird species, or 12 percent, are now considered endangered, threatened or vulnerable. Nearly one in five of the world’s estimated 10,000 species of reptiles are threatened with extinction as are about 40 percent of all amphibian species and 26 percent of all mammals. 

We need to act now to save these species with the same sense of purpose, cooperation, creativity and resourcefulness that this wonderful story of the Channel Island foxes reflects.