Birds are returning to a rodent-free island formerly known as Rat

On the island formerly known as Rat, the rats are gone and the birds are back.

So says a study by biologists that evaluated conditions at a remote Aleutian island five years after it was bombarded with rat-poison-laden pellets in one of the world's most-watched rat-removal campaigns.

"A range of terrestrial and marine birds have newly colonized, re-colonized, or increased in abundance following the eradication of invasive rats," said the study, published in the journal Biological Invasions.

The site was long known as Rat Island, a name with origins more than two centuries old. The rats that scurried ashore there from a wrecked Japanese sailing ship in the late 1700s were the first ever to invade any part of Alaska. Generations that followed dominated the island and found easy meals among the eggs, chicks and adult birds that had no natural defenses against the land-based predators.

When rats ruled, birds were noticeably scarce, said Donald Croll of University of California Santa Cruz, the lead author of the newly published study. "It was a pretty quiet island," compared to other Aleutian islands with big bird colonies, Croll said. On bird-friendly islands like Buldir, he said, seabirds are noisy day and night.

That changed after 2008, when the U.S. Fish and Wildlife Service, in partnership with the nonprofit organization Island Conservation and other organizations, mounted an aerial-supported campaign to rid the island of rats.

The following year, scientists who surveyed the island found 27 bird species represented there, compared to 20 in 2008, and with total numbers significantly higher and nests much more plentiful after eradication.

Bird species that were absent prior to rat eradication but now found on Hawadax include tufted puffins, song sparrows and snow buntings, the study said. There were no puffin burrows in 2008; in 2013, the scientists found six.

Other birds that were scarce on the island have become more plentiful. Black oystercatchers increased five-fold after eradication. Although many glaucous-winged gulls were inadvertently killed when they ingested the rat poison spread in 2008, those birds have increased in number and in breeding success; only five nests were spotted before rat eradication, but the 2013 survey found 27.

A few bird species, such as Pacific wrens, appear to have been unaffected by the rat eradication as of 2013. And one species -- the bald eagle -- took a big hit because they ate the poison meant for the rats. All but two of the 24 eagles on the island prior to eradication were lost in its immediate aftermath. By 2013, the bald eagle population had recovered to 10, the survey found. Since bald eagles have "slow life histories," recovery from the accidental poisoning is expected to take several more years, the study said.

While birds are coming back to newly renamed Hawadax, restoration of the island's vegetation will be a longer process. It might take decades for the plant cover to revert to the grasses that cover most Aleutian islands instead of the low shrubs that dominate now, Croll said. "You just have to be a little patient," he said.

A thriving bird population is crucial to Aleutian plant life, Croll said. Birds play an important role in dispersing seeds, and their presence -- specifically, their feces -- makes the very soil more hospitable for the native grasses, he said. Without bird feces, the soil is nutrient poor and supports only those plants that can grow in such conditions, like the low shrubs, he said.

Steve Ebbert, a U.S. Fish and Wildlife Service biologist, agreed.

"You know what the best fertilizer in the world is? Guano," said Ebbert, who focuses on invasive species in the Alaska Maritime National Wildlife Refuge, which sprawls across the Aleutian chain and other parts of coastal Alaska.

Rats' habit of eating plant bulbs, Croll added, helps account for pre-eradication lack of certain iconic Aleutian plants like chocolate lilies.

There are no specific plans to return to Hawadax Island in coming years to survey changes in bird and plant populations, but if anyone decides to do so, there is now a wealth of data to support future studies, Croll said.

The significance of the Rat Island eradication goes beyond the Aleutians or Alaska.

Invasive species have wreaked havoc on island ecosystems around the world, and rats are especially dangerous invaders. About 95 percent of bird extinctions since 1500 have been among species that nest on islands, according to the newly published study. Rats are even implicated in the extinction of the dodo.

But successful rat eradications have been carried out on several islands in various parts of the world.

In Alaska, where some sites, such as Unalaska and Kodiak, have long been infested and are believed to be past the point of possible eradication, remote Rat Island stood out as a poster child for destruction of native species by rats.

Spurred by the experience at Rat Island and elsewhere, Alaskans have become serious about combating rat invasions. A state law that went into effect in 2007 outlawed the possession or harboring of rats, even if it is inadvertent. A variety of local, state and federal agencies and organization have collaborated on anti-rat programs, and efforts have been particularly successful in the Pribilof Islands, which remain rat-free despite the high level of ship traffic there.

The Fish and Wildlife Service and other agencies have contingency plans, when they respond to shipwrecks, to prevent "rat spills," which could have the potential to be more ecologically damaging than oil spills.

If the Rat-turned-Hawadax experience is deemed a success, are any other islands next in line for rat eradication?

Croll, among others, has his eye on Kiska, an Aleutian island that got its first rats in World War II when it was occupied initially by Japanese soldiers and later by U.S. forces. On that island, rats threaten an important colony of auklets.

No new rat-eradication projects are planned for now in the refuge, said Ebbert, who has been tackling islands with invasive species ranging from small rodents to big lumbering cattle. Kiska in particular would pose challenges, he said. At 69,000 acres, it is 10 times the size of Hawadax and would likely cost about 10 times the $3.5 million price tag of the Rat Island eradication, he said. Other smaller islands might be more feasible candidates for rat removal, though that falls short of the ideal, he said.

"It would be great to eradicate all the rats in our refuge islands," he said.