Eleven years after scientists removed every last Norway rat from Alaska’s Hawadax Island, the ecosystem has fully healed. A 2021 study published in Scientific Reports confirms that seabirds and kelp have returned to the shoreline, restoring a food web that had been broken for two centuries. The recovery was not just partial; it mirrored the structure of nearby islands that never hosted rats.
The damage was severe. Norway rats, brought by 18th-century shipwrecks and WWII shipping, acted as an unnatural apex predator on the island. They devoured shorebird eggs and chicks, causing breeding populations to collapse. Without birds to eat them, herbivorous snails and limpets multiplied unchecked, stripping the rocks of fleshy algae and kelp. Researcher Carolyn Kurle documented this imbalance during pre-eradication surveys in 2008, capturing a shoreline ecosystem in disarray before restoration began.
In 2008, Island Conservation, the US Fish and Wildlife Service, and The Nature Conservancy executed a total eradication. They renamed the island Hawadax, reviving its original Aleut name meaning “the island over there with two knolls.” This operation gave researchers a rare gift: a complete baseline. Follow-up visits in 2013 and 2019 allowed scientists to track the trajectory against untouched neighboring islands. The data showed a clear, measurable rebound.
The mechanism was a three-level trophic cascade. As black oystercatchers and rock sandpipers returned, they resumed their role as top predators of the intertidal zone. They ate the snails and limpets. Grazing pressure dropped. Kelp cover expanded. Kurle admitted the speed surprised the team. “We were surprised that the level of recovery unfolded so quickly, we thought it could be longer,” she said. Co-author Donald Croll noted the work confirms how deeply introduced predators reshape island ecosystems.
The study underscores the viability of eradication as a conservation tool. It offers strong evidence for continued efforts on invaded islands worldwide, from remote Alaska to tropical zones. The proof is in the kelp: where rats once ruled, the original food web has returned, intact and functional.