How a Feral Pig Eradication Sparked the Fastest Mammal Recovery in US History

An aggressive campaign to eradicate 5,036 feral pigs from Santa Cruz Island triggered the fastest successful recovery of an endangered mammal in the history of the United States Endangered Species Act. According to official press releases from the US Fish and Wildlife Service and historical records from the National Park Service, the eradication program began in 2005 as part of a larger effort to save the native Santa Cruz Island fox from extinction. By 2015, the island's fox population had grown from fewer than 70 animals to about 2,100. In August 2016, federal officials removed three subspecies of the Channel Islands fox from the endangered species list.

An ecological chain reaction on the island

The decline of the Santa Cruz Island fox was caused by a chain of environmental changes linked to human activity. Feral pigs, brought to the island as domestic animals in the 19th century, later became wild and formed large populations. During the late 1980s and 1990s, the large number of pigs attracted non-native golden eagles from mainland California. The eagles fed on feral piglets but also began hunting the house-cat-sized island foxes. The foxes had lived for thousands of years without natural flying predators, so they had few ways to protect themselves. At the same time, native bald eagles had disappeared from the Channel Islands by the 1960s because of DDT pollution. Unlike golden eagles, bald eagles mainly eat fish and seabirds and naturally defend their territory from golden eagles. With bald eagles gone, golden eagles were able to settle on the islands and heavily prey on the foxes. As a result, the fox population fell by more than 90 percent.

Eradication and cooperation

Facing the threat of extinction, the National Park Service and The Nature Conservancy, which jointly own and manage Santa Cruz Island, began a major restoration program. In 2005, professional teams started removing the feral pigs. To cover the island's 62,000 acres of rugged, mountainous land, workers built 28 miles of strong, pig-proof fencing. This divided the island into five management areas. Teams used ground hunting, trained tracking dogs, and helicopter operations to find and remove the pigs. By late 2006, all 5,036 feral pigs had been eliminated. This removed the main food source that had helped support the golden eagle population. Other conservation efforts focused on the eagles. Wildlife biologists captured 44 golden eagles and moved them to northern California, away from the Channel Islands. Conservation groups also released young, captive-bred bald eagles onto the island to restore historic nesting sites and help keep golden eagles away.

Captive breeding and rapid recovery

To keep the fox from disappearing while the ecosystem was being restored, biologists created a captive breeding program on Santa Cruz Island. Park rangers and wildlife managers captured some of the remaining wild foxes and placed them in protected enclosures where they could breed safely. Before being released, the foxes were vaccinated against canine distemper and rabies, two mainland diseases that could seriously threaten an isolated island population. After the golden eagles were removed and the feral pigs were eradicated, captive-bred foxes were released back into the wild. With fewer predators and competing land animals, the population grew quickly. National Park Service surveys showed that the number of foxes increased from fewer than 70 in 2004 to about 2,100 by 2015. Similar recoveries took place on nearby San Miguel and Santa Rosa islands, where fox populations had also been severely reduced by golden eagle predation.

Official delisting and national recognition

In August 2016, the US department of the interior held a formal announcement to mark the removal of the Santa Cruz, San Miguel, and Santa Rosa island fox subspecies from the Federal List of Threatened and Endangered Wildlife. The recovery was recognized as the fastest recovery of any mammal listed under the Endangered Species Act since the law was passed in 1973. "The Island Fox recovery is an incredible success story about the power of partnerships and the ability of collaborative conservation to correct course for a species on the brink of extinction," US Interior secretary Sally Jewell said during the delisting announcement. Former U.S. Fish and Wildlife Service Director Dan Ashe also highlighted the achievement, noting that in 2004 the foxes had been given a 50 percent chance of becoming extinct within the next decade. By 2016, three of the four subspecies had recovered, while the fourth was also improving. National Park Service Director Jon Jarvis stressed the importance of the emergency captive-rearing program. He said that captive breeding was critical to saving the foxes and that restoring balance to the island ecosystem helped secure their survival. After the federal delisting, the National Park Service and The Nature Conservancy continued conservation work and introduced biosecurity measures at visitor access points. Island managers continue to monitor fox health, screen for diseases, and control the movement of animals and materials from mainland boat harbours to prevent non-native animals and harmful pathogens from reaching Santa Cruz Island.