Bird Loss Echoes on Alaska Islands;
Study calls fox infestation an ecology threat
Doug O'Harra, Anchorage Daily News, May. 22, 2005
ANCHORAGE, Alaska - It's known as one of Alaska's worst ecological disasters: Foxes introduced into scores of Aleutian Islands through the early 20th century by fur farmers ended up eating millions of nesting seabirds.
Before the invasive predators died out or were killed off from most areas, they almost drove the Aleutian Canada goose to extinction and decimated other species throughout the 1,200-mile archipelago. advertisement
But the damage went even further, delivering more than silence to the Aleutian shore. A recent scientific study of 18 islands, nine with foxes and nine without, has revealed a previously unknown ecological link between land and sea.
Minus the seasonal drizzle of guano as nitrogen-rich fertilizer, soil on many Aleutian islands simply lost the capacity to support what had been lush grassland, explained Vernon Byrd, supervising biologist with the Alaska Maritime National Wildlife Refuge and one of the study's five authors.
What once was an ocean of beach rye and other dense growth transformed into a scruffy tundra dominated by dwarf shrubs and leafy plants.
It's as though a tall forest had been shrunk to scrubland, Byrd said recently from his office in Homer.
The study has broad implications about the danger non-indigenous species like foxes pose toward isolated island habitats like those found in the Aleutians, according to the paper, published in March in the journal Science.
By knocking out key species - foxes eating up seabirds, for example - such invasive critters can cause the food chain to unravel.
The findings also give urgency to the refuge's continuing program to eliminate foxes from a dozen islands where they don't belong, Byrd said.
Two years ago, teams of trappers worked the perimeter of Adak Island, in a $150,000 project that entailed hunting down and killing foxes one at a time.
This year, teams will focus on Tanaga and Kanaga islands. A survey found foxes burrowing on high on Tanaga's volcanic slopes, possibly subsisting on ptarmigan. Russian trappers first introduced Arctic foxes on certain Aleutian Islands in the 1700s. By the early 1800s, Native Aleut people reported that seabirds were disappearing from Atka and Attu islands.
The U.S. Fish and Wildlife Service began eradicating foxes from the Aleutian Islands in 1949, employing a variety of methods ranging from poisoning to traps. By the early 1990s, the animals had been exterminated from 17 islands and had disappeared from most others, leaving foxes still present on more than 20 Aleutian islands.
Byrd, who joined the refuge staff in the late 1960s, first noticed something was amiss as he surveyed for places to reintroduce the endangered Aleutian Canada goose.
Over time, Byrd teamed up with nationally known biologist Jim Estes. Along with three other scientists, Estes and Byrd organized the study that compared vegetation and soil nutrients from fox-infested islands with places that remained fox-free.
Among other things, they found that the dense congregations of seabirds on fox-free islands produced 63 times more guano than the meager bird populations on fox-infested shores, almost 13 ounces per square meter vs. about one-fifth of an ounce.
The soil contained much higher levels of nitrogen brought from the sea in the guano. The scientist also found greater nitrogen concentrations in the grass, leafy plants, mollusks, songbirds, insects and spiders.