Feral pigs are wreaking havoc on farms. The headline caught my eye because I didn't know they could actually wipe out feral pigs. The populations are spreading. But this is on a couple islands so isolated populations. Still quite an accomplishment, and it sounds like the recovery of the land is rapidly occurring.
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5,000 feral pigs were killed to save a California national park
The bold, controversial plan to change an island ecosystem
Today, the major islands of Channel Islands National Park appear dominated by tiny foxes. They’re seemingly everywhere at times — scurrying across trails, curled up in the grass, brazenly stealing mac and cheese from campers.
The foxes number in the thousands, with more than 2,500 each on Santa Rosa and Santa Cruz, the two largest islands in the eight-island chain — yet despite their numbers here, they’re still considered to be rather rare. Originally descended from the gray fox found on the mainland, the island foxes have evolved over many years into their own species, with the island chain off the coast of Southern California serving as their only habitat. And on each of the six islands where they’re found, the fox has evolved further into its own distinct subspecies.
But until recently, the unique species was considered endangered, driven nearly to extinction by the introduction of nonnative animals on the islands. At one point their numbers plummeted to just over a dozen foxes each on San Miguel and Santa Rosa Islands. The island fox was listed as endangered in 2004, facing near “certain extinction” — until park officials came up with a drastic solution: They hired contractors to systematically kill more than 5,000 feral pigs.
A pair of foxes rest on Santa Cruz Island, Channel Islands, Calif.
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The fox population swiftly recovered once the pigs were eliminated, and the fox was removed from Endangered Species Act protections in 2016, the fastest a mammal has ever been delisted. The quick comeback is just one example of the ways that Channel Islands National Park’s flora and fauna are recovering following more than a century of ranching and nonnative species invasion on the islands, showing how quickly introducing or removing a species can impact biologically isolated islands.
Farm animals ruled islands for a century
Humans have occupied California’s Channel Islands, a chain of eight islands west of Los Angeles, Ventura and Santa Barbara counties, for thousands and thousands of years. The “Arlington Man,” known as some of the oldest human remains ever found in North America, was discovered on Santa Rosa Island and dates back to around 12,900 years before the present era. Historic Chumash village sites were also established across the northern Channel Islands of Santa Cruz, Santa Rosa and San Miguel, and Native Chumash people also spent time on the drier and smaller Anacapa Island.
But when Europeans arrived, bringing diseases and decimating food sources, the Chumash population on the islands declined. The island Chumash population relocated to the mainland by the 1820s, where many were forced to labor in missions.
Shortly after that, ranchers moved in. Santa Rosa Island was filled with cattle, sheep and horses by 1844, and by 1870, Santa Cruz Island was filled with 50,000 sheep. Ranching continued on the islands in some form until 1999. Longtime Santa Rosa Island ranching company Vail & Vickers removed the last of its cattle from the island by the end of 1998, and sheep were removed from Santa Cruz Island the next year.
Pigs were brought to Santa Cruz Island as farm animals around the 1850s. Some swine escaped, then exploded in population over the years to form a huge feral population that dominated the island. Santa Cruz Island was part of the establishment of Channel Islands National Park in 1980, though the National Park Service didn’t own land on the island until 1991. Since 2001, the nonprofit Nature Conservancy has owned about 75% of the island, with the other 25% under the National Park Service.
FILE: More than 5,000 feral pigs populated Santa Cruz Island by 2001.
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By then, more than 5,000 feral pigs populated the island of 96 square miles, and park managers had a serious pig problem to deal with.
How thousands of pigs were ‘eradicated’
In the early 2000s, thousands of feral pigs were wreaking havoc on Santa Cruz Island. The pigs uprooted native vegetation, causing erosion and allowing invasive plants to spread. They dug up and destroyed important Chumash cultural sites. They also attracted the golden eagle to the island, which preyed on the pigs but quickly began scooping up island foxes, which weren’t used to aerial predators. By 2004, the island fox (as well as 13 plant species) were all placed on the endangered species list, and park officials considered the feral pig population one of the biggest culprits. The golden eagles drawn to the island by the feral pigs were considered “the primary cause of decline of island foxes,” according to Annie Little, supervisory ecologist at Channel Islands National Park.
“It was determined fairly early on through the management of the park that the pigs needed to be removed,” Little said.
“[Removing the pigs] was a really important, fundamental action that needed to occur in order to allow the recovery of native and rare plants, and the island fox population,” she continued.
Eradicating the feral pigs was part of the National Park Service’s overall strategy to restore the islands, says Little, by removing nonnative animals that were having “tremendous impacts.” Pigs weren’t the only threat. Grazing cattle and sheep had also decimated vegetation on Channel Islands, but the last sheep were captured and removed from Santa Cruz Island in 1999, leaving the pigs as the last “landscape-level impact.”
The National Park Service and the Nature Conservancy announced the start of the Santa Cruz Island feral pig “eradication” program in March 2005, following the earlier “eradication” of feral pigs from Santa Rosa Island in 1993. But Santa Rosa Island only had about 1,000 pigs to deal with. On Santa Cruz, the issue was five times that size.
“Invasive species can have very detrimental impacts to biodiversity in general, and on islands like the Channel Islands where we have unique species found nowhere else in the world, [those species] don’t necessarily have the option to relocate to other locations,” Little said. “They may even be single-island endemic and only found on that island, while a feral pig is something you can find on the mainland. So managers often have to make these hard and challenging decisions about removing nonnative animals.”
Santa Cruz Island is part of the Channel Islands chain off the coast of Santa Barbara, Calif. The island, pictured April 24, 2015, and the Pacific Ocean around it, are part of the National Park system, and home to a rare species of fox, several species of migrating whales, as well as healthy populations of sea lions and dolphins.
The decision wasn’t without controversy. A Santa Barbara businessman, along with a couple of animal rights organizations, sued in 2005 to stop the eradication program, but the suit was dismissed in court. Much of the pushback focused on the decision to shoot the pigs, which opponents called inhumane, instead pushing for a plan that would trap and sterilize male pigs or kill the pigs by lethal injection instead, according to Los Angeles Times reporting from the time.
The pigs couldn’t just be moved to the mainland because they could carry diseases. And while “contraceptives and sterilants are sometimes useful for animal control,” they aren’t helpful “for eradication of pigs. Controlling feral pigs would not lessen their destructive impacts to island resources,” the National Park Service said at the time.
Instead, a professional hunting firm called Prohunt was brought in from New Zealand, where the company specialized in killing nonnative species on fragile island ecosystems. Santa Cruz Island was divided into five sections, and hunters killed off a total of 5,036 feral pigs by going through each section first with traps, then aerial hunting, followed by hunting on the ground.
“Prohunt’s strategic hunting approach was specifically designed to address and avoid the most common causes of failure in eradication projects,” states a 2008 report by Prohunt on the program.“Keeping pigs naive to hunters throughout the project was vital. The greatest threat to success would have been creating an educated population that was skilled in avoiding hunters.” Prohunt said it followed the American Veterinary Medical Association’s guidelines for humane euthanasia of animals.
“Taking actions like this is never something that we as conservationists, land managers and stewards take lightly. Most people go into this field because they love nature, many of us are pet owners, and we have to take these kinds of dramatic actions to save a whole suite of biodiversity,” said John Knapp, senior island scientist for the Nature Conservancy on Santa Cruz Island.
But the stakes were high.
“We are in a sixth mass extinction event. Extinction is happening all around the world. And extinction was in process on the Channel Islands, right in our backyard,” Knapp continued.
The removal of pigs was paired with the capture of 44 golden eagles, which were released back on the mainland. They were replaced by 61 bald eagles reintroduced to the island. The official bird of the United States had flown around the islands until the 1950s before being threatened by humans and chemicals like DDT. Unlike their golden counterparts, the bald eagle typically catches fish, not foxes.
By 2007, the last feral pig was killed on Santa Cruz Island. And in the 17 years since, the island has completely transformed.
An island in recovery
When Knapp started working on Santa Cruz Island, just as the pig eradication program was wrapping up, it looked completely different than it does today. The ground was heavily trampled and eroded by pigs, and the hillsides had some trees and vegetation, but there wasn’t much of an understory, which refers to younger trees and smaller plants growing underneath the older trees.
“There weren’t layers of vegetation, it was either bare ground or just trees above,” Knapp said. The feral pigs would “gobble up” acorns, stifling the growth of new oak trees on the island before they could even start to take root.
But by 2015, botanists were “completely dumbfounded by the level of complexity in the vegetation structure following the pig removal,” says Knapp. He refers to the newer trees as the “Class of ’07,” since the trees took root following the pig removal — the island had older oak trees dating back to the 1850s, before ranching took off, but very few younger trees that had grown between the 1850s and 2007.
“Now there are places where there are carpets of seedlings surrounding large oaks, and you just wouldn’t have ever seen that before,” said Knapp.
Hillsides that were previously bare soil filled in slowly with native vegetation, assisted by the aggressive removal of invasive plants by the Nature Conservancy. One canyon known as the Laguna watershed was essentially just bare bedrock with pools of water when the pigs ruled the island. Two years later, botanists started noticing native cattails in the pools, which trapped soil and set the foundation for more plants to return. A decade later, the watershed featured 20-foot-tall willow trees surrounded by Humboldt lilies. The entire area had changed from bare bedrock to riparian woodland in the span of 10 years.
In another sign of the island’s recovery, last November, two plants found only on the Channel Islands were declared fully recovered by the U.S. Fish and Wildlife Service, and delisted from Endangered Species Act protections. This included the island bedstraw, described as “a woody shrub plant with small flowers” that grows on Santa Cruz and San Miguel islands. When the plant was first listed, it numbered in the hundreds, now there are over 15,000. The Santa Cruz Island dudleya, a flowering succulent only found on Santa Cruz Island, was also delisted.
Foxes have also recovered, reclaiming their position as the islands’ tiny apex predator. Knapp estimates it took about four years of working on the island before he saw a fox for the first time, in about 2010. Now, assisted by a captive breeding program that happened around the same time as the pig eradication, foxes are everywhere. Knapp estimates it’s difficult to drive across the island without seeing at least six just out and visible along the road. Little says there’s some thought that the foxes might be soon approaching their upper limit, or carrying capacity, of the population number that can be sustained on Santa Cruz and Santa Rosa islands.
While a success for endangered foxes and flora, the feral pig eradication program was seen as controversial by some at the time — and similar programs targeting nonnative species on other islands have also faced opposition . . . .
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