In the 1700s, a shipwreck brought hundreds of rats to an Alaskan island. 11 years after scientists removed them in 2008, seabirds returned and the ecosystem was recovered

Imagine an island infested with so many rats that it earned the nickname of Rat Island. Alaska's Hawadax Island was once known as Rat Island after an 18th century shipwreck led to the escape of these Norway rodents. These resilient rats adapted and thrived in the new environment and eventually populated the island ecosystems, disrupting the natural ecological order and driving out native species. It was not until 2008 that researchers came together to get rid of the rats. Almost 11 years after the initiative, the island is not only rat-free but has developed a kelp-rich intertidal ecosystem resembling untouched islands.

A helicopter-led effort changed the island

The 2008 restoration project brought together the U.S. Fish and Wildlife Service, The Nature Conservancy and Island Conservation. To tackle the invasive population, conservationists spread poison pellets across the island from helicopters. The goal was straightforward: eliminate the rats and give native wildlife a chance to return.

Earlier observations had already shown that bird numbers improved after the eradication. But researchers wanted to know whether removing the rodents had triggered changes beyond the birds themselves.

The surprising chain reaction beneath the surface

A study published in Scientific Reports examined what happened over a longer period. Researchers compared observations made before the rat removal with findings from five years and 11 years later, looking at both bird populations and life along the island's rocky shoreline.

Rats had disrupted the food chain by preying on birds and other wildlife. With fewer seabirds around, creatures such as sea stars, snails and isopods faced less natural predation. Their numbers increased, and these small grazers consumed more of the kelp growing in the coastal waters.

Once the rats disappeared, the sequence began reversing. Seabirds returned, their presence helped bring down populations of shoreline grazers, and the kelp had an opportunity to grow again.

A louder, greener island

Researchers used other Aleutian islands as a reference because there was no detailed record showing exactly what Hawadax looked like before rats arrived centuries ago. Rat-free islands provided a useful picture of what a healthier ecosystem could resemble.

Those islands tend to be filled with seabirds during summer, creating a striking contrast with islands affected by rats. Their grasses also grow taller, partly because bird droppings enrich the soil.

After 11 years without rats, Hawadax was showing signs of moving in that direction. Native shorebirds and intertidal communities were beginning to resemble those found on islands that had never experienced a rat invasion.

Why the recovery took years

The transformation was not immediate. Researchers found that the deeper changes in the intertidal food web became clearer more than five years after eradication, highlighting why long-term monitoring matters in conservation projects.

Restoration ecologist Holly Jones, who was not involved in the study, noted that the research demonstrates how dramatically removing an invasive predator can reshape an entire food web. She also pointed out that scientists had to use rat-free islands as a comparison because Hawadax's original ecosystem could not be observed directly.

The intervention was not without consequences. Some bald eagles died after consuming the poison, although their populations later showed signs of recovery. Yet the project offers a striking example of how removing one invasive species can set off a much larger chain of ecological recovery — from returning seabirds to healthier kelp-filled coastal waters.