Evidence that more ocean-derived nutrients were cycling through the ecosystems of fox-free islands than on fox-infested islands came from analyses of nitrogen isotopes in soil, plant, and animal samples.
"The terrestrial ecosystem was being subsidized by marine-derived nutrients, and the foxes basically cut off the subsidies by interrupting the flow of nutrients coming from offshore," Croll said. "It transformed the plant community from one that does well in nutrient-rich conditions to one that does well in nutrient-depleted conditions."
Foxes were first introduced to some of the islands by Russian fur traders in the mid- to late-18th century as a way to supplement the declining harvest of sea otter pelts. But the practice escalated between the 1890s and the 1930s, when the U.S. government worked to establish fox farming businesses on the islands. Mostly arctic foxes and smaller numbers of red foxes were introduced to more than 400 islands.
Byrd, who has been involved in restoration efforts in the Aleutian islands since 1971, said most of the islands had major breeding colonies of seabirds before the arrival of foxes. There are about 26 species of seabirds that regularly nest on the islands, he said. They include surface nesters, such as gulls and terns, that lay their eggs on the ground; burrow nesters, such as puffins, that dig burrows in the soil for their nests; and crevice nesters, such as auklets, that nest in boulder piles and rock crevices.
According to Byrd, surface nesters and burrow nesters tended to disappear completely from islands with foxes, while populations of crevice nesters were reduced but not eliminated. Ledge nesters such as murres and kittiwakes, which nest on steep cliff faces, were less affected by the foxes, he said.
"Wherever the puffins and gulls have come back after the removal of the foxes, the vegetation has started
Source:University of California - Santa Cruz