In 2002, crews removed rats from California’s Anacapa Island; 10 years later, rare seabirds were returning and the island’s ecosystem was recovering

For years, something was quietly eating its way through the future of Anacapa Island. Black rats, introduced to the island most likely as stowaways on ships, were preying on seabird eggs and chicks, native deer mice and other wildlife. One of their most serious targets was Scripps's murrelet, a rare seabird whose nesting colonies were being heavily affected by rat predation.

Then conservationists attempted something that had never been simple on an island of steep cliffs, sensitive wildlife and difficult terrain: remove the rats completely.

The work was carried out in stages, with East Anacapa treated in December 2001 and Middle and West Anacapa treated in fall 2002. Years later, the results were becoming difficult to overlook. Rare seabirds were returning, murrelets were producing more successful nests, and native wildlife was recovering across the island.


Ten years after the rat removal, Anacapa was showing what could happen when one invasive species was taken out of an island ecosystem.

Why were rats such a threat to Anacapa?

Anacapa Island is part of the Channel Islands and provides important habitat for seabirds, pinnipeds and native plants and animals. Its steep lava-rock cliffs contain caves and crevices that are particularly valuable to rare seabirds such as Scripps's murrelets and ashy storm-petrels.

The island also supports the largest breeding colony of California brown pelicans in the United States and is home to a unique subspecies of deer mouse found only on Anacapa.

But the arrival of non-native black rats disrupted that ecosystem.




Rats had been introduced to Anacapa before 1940 and were believed to have reached the island aboard ships. Once established, they found seabird eggs and chicks to be an important food source.

Approximately 40% of Scripps's murrelet nests on Anacapa had shown evidence of egg predation. In another account of the problem, the rats were estimated to have consumed approximately 70% of the eggs of the once-common seabird.

The rats also preyed on native deer mice, reptiles, insects, intertidal invertebrates and plants.

The problem was part of a much wider island conservation challenge. Rats have been introduced to more than 80% of the world's islands and are estimated to account for 40% to 60% of bird and reptile extinctions worldwide.

How did conservationists remove the rats?

The effort to find a solution began in the mid-1990s, when the National Park Service worked with the Island Conservation and Ecology Group to determine whether rats could be eradicated from Anacapa.

Island Conservation and Ecology Group had experience with island restoration and knew that trapping alone had never successfully eradicated rats. More than 100 islands worldwide had used rodenticide bait for rat eradication.

Anacapa presented unusual challenges.

Its steep cliffs made it difficult to place bait within the territory of every rat. Native deer mice could also eat bait intended for rats, while California brown pelicans were extremely sensitive to disturbance and spent much of the year breeding and nesting on the island.

After extensive consultation with experts, the park and ICEG determined that bait pellets containing brodifacoum could be used.

The operation was carefully timed for the fall, near the end of the dry season, when rats were hungry and visitor numbers and bird populations were lower.

To protect the native deer mice, a small population was held in captivity, while East Anacapa was treated one year before Middle and West Anacapa.

Phase I was completed in December 2001. Phase II followed in fall 2002.

What happened after the rats disappeared?

The ecological monitoring that followed began showing substantial changes. Mouse populations returned to normal and were breeding abundantly in the wild. Juvenile side-blotched lizards and slender salamanders were also thriving without rats.

But some of the most striking changes involved seabirds.

Scientists recorded an early and dramatic response from Scripps's murrelets. In 2003, Thomas Hamer of Hamer Environmental reported, "We have detected increases in the number of birds visiting nesting colonies ranging from 58% to more than two times higher when compared to the number of detections that we recorded per night in any of the previous years."

Biologists continued monitoring the species afterward and recorded increasing numbers of nests along with consistently high egg-hatching success.

Cassin's auklets also returned to Anacapa as breeding birds following the elimination of rats, although they remained uncommon on the island.

A decade after the eradication, the recovery had become even more notable. Ashy storm-petrels were nesting on the island for the first time ever recorded, while Cassin's auklets had expanded their territories.

Most significantly, the number of Scripps's murrelet nests had quadrupled, accompanied by a 50% increase in eggs hatched.

Why does Anacapa matter to seabirds?

The recovery is especially significant because the Channel Islands provide some of the most important seabird habitat in southern California.

The islands provide nesting and feeding grounds for 99% of seabirds in the region and support 12 seabird species that depend on the islands' marine resources and isolation.

They host half of the world's population of ashy storm-petrels and western gulls, as well as 80% of the U.S. breeding population of Scripps's murrelets.

They are also home to the only major breeding population of California brown pelicans in the western United States.

The Channel Islands contain the largest breeding colonies in southern California for several seabird species, including Cassin's auklets, western gulls, Scripps's murrelets, rhinoceros auklets, tufted puffins, ashy storm-petrels, double-crested cormorants, pigeon guillemots and black storm-petrels.

Could removing rats restore an entire island ecosystem?

The Anacapa project was never only about removing one invasive species.

The National Park Service, Island Conservation, the American Trader Trustee Council and other partners viewed rat eradication as part of a broader effort to restore biological diversity on the Channel Islands.

American Trader Trustee Council funds resulting from a southern California oil-spill settlement helped support the project because restoring seabird populations injured by the spill was among the purposes of the settlement.

Island Conservation North America Regional Director Gregg Howald said, "Nowhere are the threats of extinction higher than on islands, and nowhere do we have greater opportunities to save species at risk. This successful project demonstrates the value of this critical conservation tool for other islands around the globe."

Channel Islands National Park Superintendent Russell Galipeau said, "This project was critical to protecting and restoring the rare and unique wildlife on Anacapa. The National Park Service is dedicated to ensuring a diverse, naturally functioning island ecosystem."

The American Trader Trustee Council also welcomed the recovery. Jennifer Boyce, its representative with NOAA, stated, "On behalf of the American Trader Trustee Council, we are thrilled that the settlement funds have been instrumental in the recovery of seabirds on Anacapa Island."

The project also received support from conservation organizations including the American Bird Conservancy, Pacific Seabird Group, California Audubon Society, Endangered Species Recovery Council, Audubon Living Oceans and Jean-Michel Cousteau's Ocean Futures.

American Bird Conservancy President George H. Fenwick stated, "The Anacapa Island project is precisely the type of well-designed, extensively researched, and responsibly implemented program that the American Bird Conservancy supports and encourages. The long-term benefits of rat eradication on Anacapa Island are enormous for the conservation of one of North America's most distinctive ecosystems."

The recovery did not end with the removal of rats. Channel Islands National Park has continued efforts to remove nonnative iceplant and restore native plant communities.



As the years passed, Anacapa provided a powerful example of island restoration. Removing an invasive predator gave rare seabirds greater protection, allowed native wildlife to recover and helped restore parts of an ecosystem that had been under pressure for decades.

Source: National Park Service, Channel Islands National Park, Island Conservation, American Trader Trustee CounciL.

FAQs

When were the rats removed from Anacapa Island?

The eradication took place in phases, beginning on East Anacapa in December 2001 and continuing on Middle and West Anacapa in fall 2002.

What happened to the seabirds afterward?

Scripps's murrelet nests quadrupled, eggs hatched at higher rates, and ashy storm-petrels were recorded nesting on the island for the first time.