The Aleutians have a rat problem. Scientists are trying to solve it
For millions of years, birds lived nearly predator free in the Aleutian Islands. The volcanic archipelago stretches westward for 1,200 miles from the Alaska Peninsula, dotting a border between the North Pacific Ocean and Bering Sea. Hundreds of bird species thrived here.
But then came the rats.
When a Japanese boat sank in the Western Aleutians around 1780, stowaway rats jumped ship and made it to one of the islands, wreaking havoc on the ecosystem.
The rodents proliferated during World War II, when American Navy ships traveled along the chain, expanding the rats’ domain.
“The rats are like an oil spill that keeps on spilling, year after year,” said Steve Delehanty, the refuge manager for the Alaska Maritime National Wildlife Refuge. “We would never allow an oil spill to go on for decades or centuries, nor should we allow rats to be a forever-presence on these islands.”
Rats bring a list of challenges to the islands. One: They’re a threat to birds.
The federal refuge that Delehanty manages consists of nearly five million acres of land and thousands of islands, where more seabirds breed than all of the rest of the United States and Canada combined.
But those birds are in trouble. Massive seabird die-offs in recent years have conservationists scrambling for solutions. And while there are many reasons for the decline in bird populations — rising ocean temperatures, algal blooms, and changing food sources — rats certainly play a role.
“You can have a colony that contains thousands, or hundreds of thousands, or sometimes even millions of birds,” he said. “Sadly, rats can just absolutely devastate bird populations. Seabirds, but also waterfowl and songbirds, and really the whole ecosystem.”
A couple years ago, Delehanty met with representatives from a wide range of groups, including the U.S. Department of Agriculture and the Aleutian Pribilof Islands Association, to figure out a plan to manage the Aleutians’ rat problem.
And they arrived at a fairly straightforward solution: kill the rats. All of them.
“That group collectively developed a vision of a rat-free Aleutian Islands someday, recognizing that that's really an aspiration,” Delehanty said. “There's no current plan to eliminate rats from every single Aleutian island. But wouldn't that be a wonderful thing to achieve in the coming decades?”
Already, federal agencies and conservancy groups have taken steps to at least have fewer rats.
Back in 2008, before the group decided to end the rats’ Aleutian vacation once and for all, a team of scientists traveled to Hawadax Island, formerly known as Rat Island. They dropped poison pellets out of a helicopter all over the island. And they killed the entire rat population on that island.
But, unfortunately, that’s not all they killed.
“We killed a considerable number of bald eagles,” Delehanty said. “They're not out there consuming the bait, but what they are doing is consuming a rat that died that consumed the bait. Or consuming a gull, perhaps … and you can end up with this second or third order of killing that you don't want to have happen.”
But the bird populations rebounded. Not only that — they thrived. A 2021 study published in Scientific Reports found that killing the rats led the island to rebound to its natural state. And now, Hawadax is touted as a success story for ecosystem recovery.
To be clear, the recent seabird die-offs have nothing to do with the Hawadax rat extermination. The rats were the main threat to birds on that island, and eradicating them is what led the ecosystem on that island to rebound.
Still, Delehanty and the team want to minimize collateral damage as much as possible. In August, around half a dozen scientists are planning to visit Great Sitkin Island in the Western Aleutians. Their plan is to put a small number of nonpoisonous pellets in strategic locations around the island. They’ll deposit the pellets by hand, then study how the pellets interact with the ecosystem.
“They are taking the same style of grain pellet that someday would include rat poison. But this year they're using it without any rat poison in it, just to see how it breaks down in the environment,” Delehanty said. “Does a fish eat it? Does it last in the stream for hours, or days, or weeks? That sort of thing we want to learn.”
Delehanty said they’ll report their findings to see how feasible it will really be to eradicate rats from the Aleutians. He expects to complete the study by winter 2023.