Soil damaged by feral pig rooting © Lyndal Laughlin

Introduced species and human disturbances have taken their toll on Santa Cruz Island. Today, 10 species of rare plants and animals—including the Santa Cruz Island fox—hover on the edge of extinction.

Scientists have traced the origins of this alarming decline to the impacts caused by feral animals. In the mid-1800s, European settlers imported domestic farm animals to the island. Though only small numbers of sheep and pigs may have escaped their pens during this era, they went on to form huge feral populations over the years.

When The Nature Conservancy acquired an interest in Santa Cruz Island in 1978, the island was in danger of ecological collapse. Tens of thousands of roving feral sheep had reduced much of the island’s native vegetation to stubble, soil or bedrock. Widespread erosion led to massive landslides. Many species, such as the Santa Cruz Island monkeyflower, had already disappeared.

By 1960, a native bird—the bald eagle—was also gone, poisoned by DDT that flowed from southern California factories into the ocean for decades before it was banned in 1973. The pesticide had contaminated the bird’s marine-based food supply, rendering its eggs too thin to hatch.

Following a scientific study of Santa Cruz Island’s fragile ecosystem, The Nature Conservancy eliminated 36,000 feral sheep from its property during the 1980s. The National Park Service, which owned the eastern tenth of Santa Cruz Island, followed up with the removal of several thousand more. The sheeps’ absence allowed native flora to stage a dramatic comeback during the 1990s. Whole forests of bishop pine returned, the rare Santa Cruz Island silver lotus crept back over the cliff edge where it had retreated from the sheep, and fields of blue dicks, goldfields and purple needlegrass flourished once again.

Destructive Pigs

Still, all is not well on Santa Cruz Island. Thousands of feral pigs remain, rooting up soil, destroying Chumash archaelogical sites and facilitating the spread of fennel, which grows quickly in tall, thick stands that choke out native plants. As a result of the pigs’ destructive behavior, nine species of plants on Santa Cruz Island struggle for survival. All occupy spots on the federal threatened and endangered species list.

Furthermore, the pigs have attracted a new top predator to the island — golden eagles. Considered only occasional visitors when territorial bald eagles — which eat fish and carrion, not foxes — inhabited the island, golden eagles discovered an abundant food source in the feral pigs in the 1990s and began colonizing Santa Cruz Island. In addition to feral pigs, the raptors also preyed upon the island fox. In less than a decade, golden eagles wiped out 95 percent of the Santa Cruz Island fox population.

Today, fewer than 100 island foxes exist in the wild on Santa Cruz Island, down from about 1,500. In March 2004, the U.S. Fish and Wildlife Service added the Santa Cruz Island fox and three other subspecies of island fox to its endangered species list.