Island Foxes

The Channel Islands were inhabitated by native peoples over 13,000 years ago and after their displacement by European settlers, have served many purposes like fishing, farming, and military use since then.

Introduction

Five remarkable, isolated islands are located just off the coast of southern California. Known as the Channel Islands, these islands are collectively a US National Park. The waters surrounding the islands are home to a wide variety of organisms. In fact, the water surrounding the area is a marine sanctuary that is home to over 2,000 species, including dolphins and whales. There are 145 species living on the islands that are found nowhere else on Earth. Of the 145 species endemic to the Channel Islands, 60 of them occur on Santa Cruz, the largest of the five islands.

The island fox is the only carnivore unique to California.

Michumash, the word from which "Chumash" is derived, means “makers of shell bead money."

The Island Fox

One of the most amazing animals found on Santa Cruz Island is the mysterious island fox. The five islands are over 12 miles from the mainland, a distance too far for any fox to swim. For this reason, experts still debate how the island fox first arrived on the islands. The most commonly agreed upon theory is that a group of native people, called the Chumash, brought gray foxes from the mainland over 7,000 years ago.

Large organisms typically need more water, food, and space than small organisms. Due to the limited resources on the island for the foxes, the smaller individuals over generations lived and thrived. This gradual change of a species in an ecosystem is commonly called natural selection. The ancestral gray fox gradually evolved into today’s island fox. Weighing in at just over 1 kg (2.35 lbs), the island fox is smaller than most house cats. They are the smallest species of fox in the world!

The only large native predators of the foxes on the islands are bald eagles. Even though the two species cohabitate the islands, bald eagles don’t prey on island foxes. Without the immediate threat of predators, island foxes have evolved with little to no notion of fear. Researchers who study island foxes can simply pick them up and hold them on their laps! Unfortunately, the Santa Cruz Island ecosystem experienced many changes that almost wiped out the island fox population. In 1994, fewer than 100 island foxes remained in the wild. What changes caused this charismatic species to all but disappear?

Ecosystem Under Stress

Around 1850, ranchers brought pigs to Santa Cruz Island from the mainland. Before long, many of the pigs broke free and found their way into the wild. Free to roam the island, the pigs reproduced rapidly and caused devastation to the ecosystem by overfeeding on local vegetation.

An estimated six million feral pigs live in the United States and cause billions of dollars worth of damage each year.

Domestic pigs were first introduced to the Americas in the sixteenth century.

Even with the arrival of their new neighbors, the pigs, it took over 100 years before the island foxes began to experience the effects of change. In the 1940s, the US government used a pesticide called DDT (dichloro-diphenyl-trichloroethane). The pesticide was invented to protect soldiers from insect-borne diseases like typhus and malaria. Because DDT was so effective at killing disease-carrying insects, farmers across the country began spraying it on their crops to protect them from the insects.

Because DDT was so effective at killing disease-carrying insects, farmers across the country began spraying it on their crops to protect them from the insects.

Unfortunately, after years of study, researchers found that DDT caused cancer and killed large numbers of untargeted wildlife. The pesticide that washed off crops during rains would find its way into waterways, creeks, and rivers. Fish and aquatic plants in these ecosystems absorbed the chemical. In turn, bald eagles and other predatory birds suffered DDT poisoning as a result of feeding on contaminated fish.

DDT affected the bald eagles’ ability to produce firm eggshells, and as a result, their population plummeted. By 1967, bald eagles were listed as an endangered species. In 1972, the use of DDT was banned nationwide. But it was too late for the bald eagles of the Channel Islands; their population became extinct.

By 1990, golden eagles found their way to the Channel Islands. Before the introduction of pigs to the islands, there wasn’t enough prey to support two populations of eagle on the islands. The decline of bald eagles, which are highly territorial, likely also helped the golden eagle colonize the islands. Unlike bald eagles, which primarily eat fish, golden eagles preferred to eat piglets inhabiting the island. The golden eagles also developed a taste for island fox. Having no fear of predators, the island fox became an easy target for the eagles.

The bald eagle is found across most of North America, especially near bodies of water where it can catch fish swimming near the surface of the water.

The golden eagle is found across North America, Europe, Asia, and parts of North Africa. Golden eagles eat a wide range of small animals.

From 1994 until 2000, golden eagle predation on the foxes was so severe that the island foxes nearly became extinct. Their population plunged from over 1,500 foxes to fewer than 100 in under ten years.

Rescue Mission

Witnessing the disappearance of foxes, Channel Islands National Park started a fox recovery program in 1999. Additionally, the Nature Conservancy and its partners started the Island Fox Recovery Program in 2002. Researchers ensured the survival of the foxes by vaccinating them against diseases, monitoring them in the wild, and introducing captive breeding. Even with the recovery plan in place, the US Fish and Wildlife Service listed the island fox as an endangered species in 2004.

With the threat of island fox extinction, scientists and experts developed a multi-staged plan to ensure the survival of the foxes:

Continue the captive breeding program. By continuing the program, scientists made sure that the island fox would not go extinct.
Eradicate the non-native feral pigs. The experts got rid of all 5,000 pigs roaming the island, cutting off the golden eagles’ main food supply.
Trap golden eagles and release them on the mainland. By trapping the golden eagles and moving them elsewhere, the island foxes’ sole predator disappeared from the island.
Reintroduce bald eagles to the Channel Islands. By reintroducing the bald eagles to the island, the golden eagles had no space to inhabit if they tried to return to the island.

The plan was a monumental success. In 2008, captive breeding ceased and the foxes returned to the islands. With record-breaking speed, the foxes were removed from the endangered species list in 2016.

With the introduction of pigs, the use of DDT, and the invasion of golden eagles on the island, the island fox ecosystem has undergone many changes over the last 150 years. Many of these changes were influenced by humankind, but fortunately, by restoring the native ecosystem, there are now over 2,100 island foxes roaming Santa Cruz Island. Scientists, however, have more work to do -- some non-native species still remain on the island.