Arctic foxes plunder Aleutian seabirds

The introduction of Arctic foxes to about 100 islands in Alaska’s Aleutian Islands has caused the seabird population to decline so much that grasslands have been reduced to tundra, new research suggests.

“One of the things this underlines is how much of an impact introduced species can have on island ecosystems,” said Dan Croll, co-author of a recent study published in the journal Science. “By far and away, most of the extinctions have been of island species, globally. And one of the biggest causes is introduced species.”

The study suggests the introduction of predators can cause other harm as well because Arctic foxes are cutting off the flow of nutrients to the islands by killing the “delivery agents,” seabirds such as puffins, auklets and gulls.

As a result, the foxes have completely changed the environment from tall grasses dependent on nutrient-rich bird droppings to tundra with dwarf shrubs and herbs.

Foxes first arrived in the Aleutians as replacements for declining sea otter populations. By the time the introductions were stopped in the 1930s, foxes were living on more than 400 Alaskan islands.

The study compared the bird populations of nine islands with foxes living on them to those on nine islands where the predators are absent. The results suggested that fox-free islands had an average of 688 breeding birds per acre.

With the foxes, the number dropped to just under nine birds per acre.

On one 2,000-acre island, researchers calculated a breeding seabird population of 1.7 million. On a similarly sized fox-filled island, researchers counted a population of 7,000.