‘Rat Island’ rid of invading rodents

A Norwegian rat imprisoned on Hawadax Island. Photo courtesy Shauna Reisewitz

Hawadax Island in the Aleutian Archipelago, long known as Rat Island after rats fled shipwrecks as early as the 18th century, has regained its ecosystem and the waders have returned to restored pre-invasion environments.

“We were surprised that the recovery developed so quickly. We thought it might take longer, ”said Carolyn Kurle, lead author of a new study on the” Isle of Rats “study published in Scientific Reports in early March and online at www.eurekalert.org, the American Association’s website for the advancement of science.

Kurle, who has participated in research expeditions to over 35 islands in the Aleutian chain, is an associate professor in the Department of Life Sciences at the University of California at San Diego, Department of Ecology, Behavior and Evolution.

Others who participated in the study included researchers from UC Santa Cruz, Island Conservation, the U.S. Fish and Wildlife Service, and The Nature Conservancy.

The team conducted surveys in Hawadax in 2008 when invasive rodents were dominating the island’s ecosystem. The Aleutian word Hawadax means “the island over there with two hills”.

When rats first came to the island, they disrupted the food chain, hunted wading bird eggs and chicks, and nearly wiped out the island’s breeding wader population. With no birds to eat herbivorous coastal invertebrates such as snails and limpets, the island’s tidal herbivores flourished, driving back the abundance of seaweed.

To reverse these effects, a coordinated conservation strategy was put in place, which was a rare case in which researchers were able to obtain ecosystem data from surveys during rat dominance, with a recovering ecosystem five years later and a fully restored system after 11 years to compare.

“You don’t often have the opportunity to go back to a remote location and collect data afterwards,” said Kurle. “Sometimes it’s hard to say that a conservation action has had any impact, but in this particular case we have taken a conservation action that was expensive and difficult, and we’ve actually shown it to work. But we didn’t expect it to happen so quickly. “

These rats are almost always direct predators of native animals when introduced to islands, Kurle said. “When the birds returned, it created a completely different structure in the marine community on this island. It now has a structure that is more in line with what we see on islands where rat invaders have never been seen before. “

According to researchers, more study is now needed to understand and measure both the direct and indirect effects of these invaders and how interconnected communities react after their removal.

This study confirms both the profound effects of introduced species such as rats on fragile island ecosystems and the remarkable conservation benefits of their removal, said Donald Croll, study co-author and professor at UC Santa Cruz Department of Ecology and Evolutionary Biology.