Achieving Balance: Anacapa Island Ten Years After the Removal of the Black Rat
6 March 2013
Ten years after removing nonnative rats the ecosystem on Anacapa Island, including rare seabirds, is showing profound results of recovery.
Ashy storm-petrels are nesting on the island for the first time ever recorded and Cassin’s auklets have expanded their territories in the absence of rats as predators. Significantly, the number of Scripps’s murrelets nests has quadrupled with a 50 percent increase of eggs hatched.
Rats are known to have negative impacts to island ecosystems. Rats are the most significant cause of bird extinctions on islands and are estimated to be responsible for half of bird and reptile extinctions worldwide.
Nonnative black rats, which were first reported on Anacapa Island in the early 1900s, threatened critical breeding habitat for these rare seabirds. They were eating approximately 70 percent of the eggs of the once common Scripps’s murrelet, a state-listed threatened species. They also preyed upon native deer mice, reptiles, insects, intertidal invertebrates, and plants.
Rat Island cleared of rats after 230 year infestation
Rat Island is officially rat free
October 2013. Biologists have confirmed that Rat Island, a remote island in the Alaska Maritime National Wildlife Refuge, is now rat-free for the first time for 230 years. The report comes after two years of careful field monitoring at Rat Island, where the invasive predator caused major declines on native bird populations by preying on eggs and chicks and altered the native ecosystem in numerous ways.
Largest rat eradication in Northern Hemisphere
Restoring habitat on Rat Island to benefit native wildlife is the largest rat eradication ever undertaken in the Northern Hemisphere and the first in Alaska. The eradication of the non-native rats took place in September of 2008 after four years of planning. The restoration of the 10-square-mile island was accomplished by Island Conservation, The Nature Conservancy and the U.S. Fish and Wildlife Service.
7,000 acres reclaimed for wildlife
“Rat Island is the most ambitious restoration effort we’ve undertaken on a refuge island, and we couldn’t have done it without our partners,” said Geoff Haskett, regional director of the U.S. Fish and Wildlife Service. “Nearly 7,000 acres of wildlife refuge habitat has been reclaimed for native wildlife and that is an exciting result.
Giant song sparrow increases
Biologists have confirmed increased numbers of at least one native bird after just two rat-free nesting seasons on the island. The giant song sparrow, found only in the central and western Aleutian Islands, is now commonly occurring on Rat Island. Song sparrows were only rarely seen on the island prior to the restoration. Other species confirmed nesting on the island and expected to benefit from rat removal include black oystercatchers, glaucous-winged gulls, pigeon guillemots, rock sandpipers, common eiders, red faced cormorants and gray-crowned rosy finches. Over the long term, burrow nesting seabirds, driven from the island by rats, are expected to return and re-colonize the island.
“The presence of nesting birds is deeply gratifying,” says Bill Waldman, executive director of the non-profit Island Conservation. “Our field team was overjoyed to see so many song sparrows this year after working on the island for several years with only an occasional glimpse of one.”
Arrived in 1780
Though Rat Island is a remote island in the Aleutian chain about 1,300 miles west of Anchorage, invasive Norway rats arrived via a 1780′s shipwreck preying on native birds and altering the native vegetation during the ensuing 220 years. The Rat Island restoration is the most recent project in a long campaign to restore otherwise healthy seabird habitat in the Aleutians.
“We’re incredibly pleased to see this fresh new start for Rat Island,” said Randy Hagenstein, director of The Nature Conservancy in Alaska. “In the Aleutians, great clouds of seabirds normally fill the skies over islands teeming with life. The rats’ devastation had turned Rat Island into an eerily quiet place.”
The U.S. Fish and Wildlife Service has been at work in the Aleutian Islands, most of which lies within the Alaska Maritime National Wildlife Refuge, restoring seabird habitat by eradicating non-native species for more than four decades. Non-native foxes have been taken off over 40 islands in the refuge including Rat Island but this was the first rat eradication for the refuge.
To ensure that invasive rats don’t spread to other globally significant seabird habitats in Alaska, the U.S. Fish and Wildlife Service leads the ongoing Stop Rats! campaign to help ships, harbours, and towns to prevent the spread of rats.
“The history of Rat Island shows we need to prevent future disasters caused by invasive species. Alaska is almost entirely rat-free, and it’s absolutely vital we work together to keep it this way. Birds that build nests on the ground – such as ducks, seabirds and songbirds – simply can’t defend their eggs and chicks from non-native predators such as rats,” said Haskett, Alaska Regional Director of the U.S. Fish and Wildlife Service.
300 successful rat eradication programmes
Island habitat restorations are occurring across the globe. Worldwide, there have been more than 300 successful eradications involving invasive rodents. Rats are responsible for about half of all bird and reptile extinctions on island habitats.
In 2008, the Rat Island Wildlife Habitat Restoration team spread grain-based bait pellets across the island from helicopters flying a GPS-guided flight path.
Two years of monitoring following international standards revealed no sign of rats. Although initial non-target mortality was higher than expected, no sign of any additional bird mortality was observed in 2010 and populations of affected bird species are already recovering on Rat Island.
With the rats gone, restoration partners and the Aleutian Pribilof Island Association agree that an Aleut (Unangan), name would be a fitting tribute to the restored island. APIA is now taking steps to enact a name change. Once a name is selected, it will await approval from the U.S. Board on Geographic Names.