One Alaskan Island’s Fight For A Rodent-Free Future

7:02 minutes

a logo of a black rat silhouette crossed out with a red sign on the side of a car
A U.S. Fish and Wildlife vehicle on Adak Island promoting rat eradication. Credit: Jennifer Pemberton/KTOO

state of science iconThis article is part of The State of Science, a series featuring science stories from public radio stations across the United States. This story, by Theo Greenly, was originally published on KUCB.

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?”

a snow covered island
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. Credit: Sarah Welter

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.

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Segment Guests

Theo Greenly

Theo Greenly is a reporter with KUCB Radio in Unalaska, Alaska.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. And now it’s time to check in on the state of science.

SPEAKER 1: This is KER–


SPEAKER 3: St Louis Public Radio–


SPEAKER 5: Iowa Public Radio News.

IRA FLATOW: Local science stories of national significance. Alaska is known for its incredible wildlife– moose, wolves, caribou, bear. But on one island, the most notorious creature just may be the rat. Yeah. These invasive rodents were so prolific on one of the Aleutian Islands that it used to be known as Rat Island.

I know what you think about rats. But scientists faced a dilemma– how do you get rid of the rats without getting rid of everything else? The good news– the island is considered a success story for bringing an ecosystem back to its natural state. Here to tell us more about this unique story is Theo Greenly, reporter for the public radio station KUCB in Unalaska, Alaska. Welcome to Science Friday.

THEO GREENLY: Yeah, hi. Thanks for having me.

IRA FLATOW: Theo, can you set the scene for us? We can gather from its old name that it had a lot of rats. But what is the ecosystem like there?

THEO GREENLY: Right, so first, let me just place this island within the larger geography. So this island is part of the Aleutian chain. So this is hundreds of islands, dozens of volcanoes that stretch from Alaska all the way across to Russia and kind of make a boundary between the North Pacific Ocean and the Bering Sea. What was formerly known as Rat Island is way out in the western Aleutians. It’s this vibrant green, kind of richly biodiverse tundra environment and ecosystem.

IRA FLATOW: So how did the rats get on the island in the first place?

THEO GREENLY: Well, in the 1780s, there was a shipwreck, a Japanese shipwreck, and there were no survivors. I should say there were no human survivors. But you can tell where this is going. There were some survivors that swam to shore. And those, of course, were rats, the Norway brown rat to be specific.

IRA FLATOW: And why were the rats so bad? Did they just become fruitful and multiplied all over the place?

THEO GREENLY: Well, yeah, they certainly did. They got to this island– the traditional name is Hawadax Island– and they just found thousands and thousands of seabirds and songbirds. And they basically just met this buffet of birds.

For millions of years, there were no land predators. There were no mammals on this island. So these seabirds that live out at sea really only go to land to nest. And so they find these remote islands where they can lay their eggs and not have to worry about predators– until, of course, the rats come.

So here’s Steve Delahanty. He’s the manager for the Alaska Maritime National Wildlife Refuge. He manages all of the federal land that is preserved under this refuge.

STEVE DELEHANTY: The rats are like an oil spill that keeps on spilling year after year after year. And we would never allow an oil spill to just go on for decades or centuries. And I don’t think we should allow rats to be a forever presence on these islands, either.

IRA FLATOW: So walk us through some of the strategies for getting rid of all those rats.

THEO GREENLY: Well, you know, Ira, you’re in New York. You, I am sure, are no stranger to the rat.

IRA FLATOW: No, I know they use rat poison and all kinds of stuff here.

THEO GREENLY: Yeah, so I mean, anybody who’s ever run into a problem with a rat knows that there are basically two things you can do. You can trap it, or you can kill it. And trapping a rat in a larger area is very, very impractical, because you can’t just get rid of some of the rats or most of the rats. You have to get rid of all of the rats, because if there’s two left to mate, or one pregnant female, you’re going to be right back where you started from pretty quickly.

So in 2008, Fish and Wildlife Service and some conservancy groups and different organizations, they went out to Rat Island. And they took the poison route. And they dropped rodenticide– they dropped rat poison– all over the island from helicopters.

And it worked. They killed all of the rats. But unfortunately, that’s not all they killed. They also wound up killing a bunch of birds, which was the very thing that they wanted to save in the first place.

IRA FLATOW: Oh my goodness. Unintended consequences.

THEO GREENLY: Yeah, sort of collateral damage, if you will.

IRA FLATOW: Yeah. So have the seabirds come back at all? Have they recovered?

THEO GREENLY: Depending on who you ask, the answer is either yes or oh my gosh, yes, yes, yes. So this 2021 study– they went back to see how the island had rebounded. And they were blown away, because not only did the seabirds and the songbirds rebound, tufted puffins were found in the area. And that’s the first time that that had happened.

But also, the whole ecosystem had returned, because the rat, it doesn’t just end with eating the birds. It goes through the food chain down to the algae, and everything just gets out of whack. So when they went back and studied how the island rebounded, they found that the island now is very similar to similar islands that never had rats introduced in the first place.

IRA FLATOW: And so scientists will continue their research over the summer. Tell us what they’re doing, what they will be doing.

THEO GREENLY: Well, these scientists sort of have a puzzle that they need to solve, which is to replicate the success of Hawadax Island but minimizing the collateral damage. So what they’re doing this summer is they’re going out to this other island in the area, Great Sitkin Island, and they’re taking grain pellets that do not have any poison in them. They’re the same kind of pellets they used for the rat poison, but these are just benign grain pellets.

And instead of dumping them out of helicopters, what they’re going to do is place some very strategically in different locations. And with cameras, they’re going to monitor how these pellets interact with the system. Where does it break down in water? Where does that go? Does a rat eat it here? Would a bird eat it there? And they’re going to basically create a feasibility study that will see if this is something that is replicable so that they can continue eradicating rats from different islands.

IRA FLATOW: A little case study to see how it works. Thank you, Theo, for an interesting story.

THEO GREENLY: Yeah, thank you, Ira.

IRA FLATOW: Theo Greenly, reporter for public radio station KUCB in Unalaska, Alaska. And if you want to read Theo’s full story about what used to be known as Rat Island, you can head over to our website, sciencefriday.com/stateofscience.

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