For years feral cats outcompeted endangered foxes on San Nicolas Island, off California's coast. (Island Conservation)
ONE HUNDRED fifty miles off the coast of Baja California, jagged Guadalupe Island climbs more than 4,000 feet above the Pacific. Throughout the year elephant seals, Guadalupe fur seals and scores of seabirds call this volcanic island home. They dive for fish in the island’s rich waters and use the secluded shoreline to escape white sharks, recuperate from migration and raise their young. Today, the isolated landmass supports a thriving community of rare plants and animals. But it wasn’t always this way.
In the 19th century, Russian and American sealing ships hunted Guadalupe fur seals to near extinction. In the end, the seals survived, but at least nine other island species weren’t so lucky.
To ensure that returning ships would have a supply of fresh meat, the seal hunters left goats on Guadalupe Island. The goats thrived, chomping away at the island’s unique flora, and their numbers swelled from a few dozen to 10,000. By 2001, when UC–Santa Cruz conservation biologist Don Croll arrived on the island, it was mostly barren. “There had been zero new trees on the island for over 100 years because the goats ate anything that tried to grow,” says Croll.
Croll traveled to the island as part of a collaborative effort between Island Conservation, the Santa Cruz–based organization he co-founded, and the Mexican government. Initially the team constructed fences to stop goats from grazing around a small number of enduring native pine trees. The results were impressive.
“A year later there were hundreds of seedlings. We even found species that were thought to be extinct,” says Croll. “We realized that if the goats were removed from the island, the native plant community would explode. We had to make [the eradication] happen.”
And they did. By 2007 the island was goat-free, most of them having been rounded up, shipped to the mainland and sold in butcher shops.
Until Guadalupe Island, Island Conservation had focused on seabird and native vertebrate recovery, not on plants, explains Croll. “With animals, we often wait three to five years before seeing a response to an invasive species removal. But on Guadalupe Island, plants sprang up the next year—it rained and the island came back to life.”
For Croll, Guadalupe Island was an eye-opening project. It showed the power of eradications as a conservation tool; on one side of the fence there were just goats and dirt, while on the other side a rare island community flourished.
In his office at UCSC’s Center for Ocean Health, Croll explains that modern transportation systems have enabled non-native species to invade about 40 percent of the world’s islands. These species quickly take over, exploiting naïve animals that never learned to defend themselves against predators. Croll adds that although islands make up only 3 percent of the world’s land mass, island species comprise 45 percent of all critically endangered species. That means a huge portion of the planet’s rarest biological treasures also happen to be, by virtue of their location, at the greatest risk of being wiped out by invaders.
Fortunately, the isolation that makes islands susceptible to invasive species also makes it possible to erase those species completely.
In the 1950s, cats brought by personnel to a naval research facility on San Nicolas Island, 61 miles off Southern California and part of the Channel Islands National Park, abandoned their owners for the wild. Generation after generation, the feral cats lived off the island’s abundance, threatening to eliminate native birds and lizards and taking food from the endangered San Nicolas Island fox. But in 2009, a team of organizations, including Island Conservation, began removing the feral cats in an effort to protect the island’s endemic and endangered species. This past February the team declared the project a success. All the cats have been trapped and flown from the island to a facility in Ramona, Calif., where they are cared for (some have even been adopted).
“Eradications are successful because islands are well-defined ecosystems: the system ends at the shoreline,” Croll explains. “On continents, ecosystem boundaries are hard to define, so it’s hard to know where one ends and the next begins. But on an island you can say, ‘I’m going to protect this island ecosystem.’ It’s clear what you are doing.” Because their actions occur in a defined space, researchers gain a clear picture of how they alter an island’s ecosystem, he adds. That’s hard to see on continents.
San Nicolas Island marks Island Conservation’s 70th successful eradication since Croll and his research partner Bernie Tershy formed the nonprofit in 1997, inspired by the story of a scientist who landed on an island full of pigs decades ago and changed it forever.
In 1958, Kenneth Stager and his rifle landed on Clipperton Island, a small coral outcropping off the western coast of Mexico. Stager, an ornithologist, had traveled there to study a supposedly vast population of boobies, a ground-nesting seabird. Instead, he found pigs.
The pigs had probably arrived on the island around 1897, when a ship wrecked on the surrounding reefs. For 60 years they trampled booby nests and ate their eggs, reducing their numbers from many thousands to just 650.
Stager took action. Walking the narrow ring of land encircling the atoll’s central lagoon, he shot the pigs, 58 in all. Ten years later, the booby population was 20,000. By 2003, it had soared to 137,000.
The pigs on Clipperton Island did what all invasive predators do: they adapted quickly to a new environment and spread uncontrolled. Sadly, the pigs paid the price for human error in a world where even the most isolated places feel our influence. It’s ironic, but some scientists kill to conserve life.
Stager’s success motivated Croll and Tershy. “If you’re thinking about seabirds, you think about invasive species and the impact they have on islands where they breed,” says Croll. “When we looked around, the New Zealanders were the only ones addressing the problem. We wanted to do something, so we started Island Conservation.”
Island Conservation’s first U.S. project focused on reclaiming threatened seabird habitat from black rats on tiny Anacapa Island, part of the Channel Islands chain. It worked, allowing rare birds and native mice to recolonize the rocky outcrop.
Last summer, the organization scrubbed rats from a rare ecosystem on a remote Pacific atoll called Palmyra. It took seven years of research and navigating legal labyrinths, but for now Palmrya’s myriad seabirds can nest in peace.
Rats Run Amok
Clipperton Island’s pigs may have started this movement, but rats are its bread and butter, so to speak. “[Rats] are interesting in that they are so successful,” Croll says. “They’ve colonized much of the world, and there aren’t too many animals that can do that. Their success is probably due to their relationship with people.”
People bring rats to islands, mostly by boat. They arrive in cargo, scurry down ropes or jump ship—usually because the boat is sinking.
On Anacapa Island, rats probably arrived when the paddleboat SS Winfield Scott ran aground on Dec. 1, 1853. All 400 passengers swam safely ashore. So did the rats.
For nearly 150 years, rats plagued the seabirds of Anacapa, eating their eggs and chicks. In one survey, 40 percent of Xantus’s Murrelet nests on Anacapa had lost eggs to rats. These quail-sized seabirds nest on just 13 islands off southern California and Baja, Mexico. They’re considered threatened because of their low numbers. It took an oil spill off Southern California to trigger a chain of events that improved their chances.
On Feb. 7, 1990, waves swung a loose anchor into the side of a tanker while it transferred oil ashore in Huntington Beach, puncturing the hull in two places. More than 400,000 gallons of oil poured out, killing about 3,400 birds.
To compensate for such loss of life, companies responsible for oil spills must pay mitigation fees to restore damaged habitats. Prior to this incident, mitigation money was reserved for the affected region, says Croll. But Island Conservation scientists argued that restoring seabird habitat on Anacapa, 80 miles north of the spill site, would have a more profound impact. The council overseeing the funds agreed, and in December 2001 Island Conservation teamed up with the Channel Islands National Park Service personnel to eradicate rats on Anacapa Island.
Bait From the Sky
Anacapa consists of three long, narrow strips: West, Middle and East Anacapa. To reduce unwanted deaths of birds and the islands’ native deer mouse, researchers staggered the eradication over two years. First, they spread poisoned bait on East and Middle Anacapa, and a year later on West Anacapa. Although seabirds aren’t attracted to the bait, the team nevertheless scheduled the dispersal for December, when most seabirds are offshore and rats are hungriest.
The island’s native deer mouse was of special concern; the eradication would almost certainly decimate their population. To prevent this, the team did thorough studies to figure out how many native deer mice would be required to successfully recolonize the island after the eradication. Then, before each eradication, they captured a few hundred mice and released them afterward.
The islands’ raptors—mainly owls, peregrine falcons and red-tailed hawks—also were a concern. Prior to the initial eradication, researchers from UCSC’S Predatory Bird Research Group captured and relocated about two-thirds of those birds to minimize deaths from eating poisoned rats.
When the eradication began, the team used a helicopter equipped with GPS to track their position and a mechanized bait-spreading bucket to scatter the bait evenly over the rugged terrain. “Anacapa paved the way for aerial bait dispersal in North America,” explains Alex Wegmann, project manager at Island Conservation. “It’s been happening in New Zealand for decades, but only recently in North America.”
The eradication worked; all rats on Anacapa died. The ecosystem began changing almost immediately. “We predicted [recovery to occur over] a five-to-10-year time scale,” says Croll. But within a year, the murrelet population was growing. Most surprising of all, Cassin’s Auklets showed up on Anacapa. The auklets, Croll notes, had never been seen there.
In the years after the eradication, teams of researchers monitored the ongoing changes. The populations of all seabirds and native deer mice are higher now than before the eradication, one team reported in the December 2009 issue of the conservation journal Oryx. Another team found that within seven years the number of nesting Xantus’s Murrelets increased by 93 percent, and the number of murrelet egg hatchings went up by 70 percent. For researchers, this confirms that rats were altering Anacapa’s island ecosystem—a system that is becoming rare.
The Palmyra Purge
Last June, Island Conservation jetted to the remote Pacific island of Palmyra. Palmyra, a U.S. territory, sits within the Line Islands, a chain of small tropical atolls 1,000 miles southwest of Hawai‘i in the central Pacific. “When you’re [on Palmyra] you can spend hours with your jaw down to your stomach just looking at the place, it’s so gorgeous,” says Wegmann. “But it’s heavily altered from military use during World War II and the rat infestation.”
During the war, the U.S. Navy used the island as an air station. Most likely, they brought with them the rodents that have devastated Palmyra’s ecosystem. For decades rats have preyed on exposed seabird nests on the ground and in trees. In turn, the drop in bird guano has depleted Palmyra’s soil of important nutrients, allowing hardy coconut palms to overtake 45 percent of the land. Coconut palms then provide food and shelter for the rats.
This palm-rat cycle has done a number on the atoll’s biodiversity, according to Wegmann. “On Palmyra we are working to conserve the whole ecosystem,” he says.
The atoll is home to 10 species of nesting seabirds, five types of land crabs, many reptiles and insects and a rare combination of plants. It’s also an important pit stop for migrating birds. “By eliminating rats on Palmyra, we have the opportunity to restore an entire ecosystem, the only one of its kind under [U.S.] federal protection,” says Aurora Alifano, the project’s safety director and head of its land-based baiting team, going on to explain that the plant and animal communities native to Palmyra were once found on many surrounding atolls. But today Pisonia forests like those found on Palmyra are vanishing. Fortunately, Palmyra became a National Wildlife Refuge in 2001, and the past decade of protection has helped shelter it from the human influences that overtake many native island species. Says Alifano, “Palmyra is a rarity.”
Wegmann concurs. “Palmyra is orders of magnitude healthier than any of the other moist tropical forests in the central Pacific.”
Last June, after seven years of preparation, a team of 40 specialists from Island Conservation, the U.S. Fish and Wildlife Service and The Nature Conservancy of Hawai’i took action on Palmyra. Helicopters distributed bait from the air, while ground crews used sling shots and air cannons to fling bait balls into palm trees.
The project broke new ground in the conservation field, says Bill Waldman, Island Conservation’s executive director. It’s the first project to restore an island ecosystem with a combination of high rat densities, masses of land crabs and the strict regulatory constraints associated with National Wildlife Refuge status. The techniques should lead to other restoration projects to protect species on islands that had seemed off limits, Waldman says.
Today, Palmyra appears to be rodent-free, but rats are sneaky. Researchers won’t know whether they’re gone for good for at least two years. To begin the monitoring process, researchers from Croll’s and Tershy’s Coastal Conservation Action Lab returned to Palmyra in August 2011 and deployed hundreds of devices to find any surviving rats. Not one appeared. The island will get a checkup in August 2012.
None of this is a permanent fix, Wegmann says. In 2000, four decades after Kenneth Stager relieved Clipperton Island of pigs, rats showed up, probably having jumped ship when a fishing boat wrecked there. The team has put controls in place on Palmyra to prevent a similar reinfestation. But the underlying problem isn’t going away.
“Commerce is not going to slow down, and people are not going to stop expanding into new areas,” Wegmann says. “Islands will continue to be threatened by invasive species. That’s why it’s so important to fight for them. As long as we value nature and the conservation of natural systems, [eradications] will be one of our most effective tools to preserve them.”
Jonah Mulski is completing a degree in ecology and evolutionary biology at UCSC.