|
|
||||||||||||||||||
|
Restoration Takes FlightPage 3
Their disappearance triggered the beginnings of an ecosystem crash scientists call a trophic cascade. With no bald eagles left to defend their historic territory, golden eagles began cruising over from the mountains of Southern California. While bald eagles largely prey on fish or eat carrion, golden eagles tend to target land animals, and they found a year-round food supply in the pigs rampant on the island’s hillsides. By the 1990s, they were nesting and enjoying the easy pickings. Once established, the golden eagles discovered another tasty food source: the island fox. At 4 to 5 pounds, this diminutive mammal is smaller than the average house cat. Biologists believe the fox made its way from the mainland to Santa Cruz more than 18,000 years ago by floating on storm debris. Like the mainland gray fox, it is an opportunistic forager, feeding on native deer mice, and ground-nesting birds and their eggs, as well as holly, nightshade and cholla cactus. As the island’s top predator, the foxes gradually became bolder and more active during the day than their nocturnal mainland predecessors. A Rapid Ecosystem Breakdown—and a Swift Response By 2000, the fox population had plummeted from the historic average of around 1,500 to fewer than 100. Without intervention, the island fox seemed doomed to extinction. In 2004 the fox earned a spot on the federal endangered species list. “The bald eagle was already gone,” says the Conservancy’s Vermeer. “If we didn’t take action, it’s pretty much a sure bet that the fox would disappear, too.” What’s alarming about Santa Cruz is the rapid pace of the ecosystem breakdown. Sheep and pigs had been destabilizing the system since the 1850s, but the damage caused by DDT triggered an abrupt collapse. The near demise of the fox occurred within a decade. The swift onset of these threats challenged Conservancy and Park Service officials to mount an immediate, sometimes hard-nosed response. The bald eagle program uses money from a 2001 court settlement with chemical companies over the DDT discharges. Biologists have imported 61 young eagles, raised in Alaska and the San Francisco Zoo. Citing the recent recovery of brown pelicans in the area, they believe concentrations of DDT have abated enough to allow the eagles to survive. The birds are placed in screened towers set high on Santa Cruz’s ridge tops overlooking the sea. They are kept in the towers for about a month to acclimatize to the island, in the hope that they will remain and resume historic patterns of breeding and nesting. Once the birds reach sexual maturity, biologists hope they will establish their own nests, driving off any golden eagles that try to return to the area. Now in its fifth and final season, the bald eagle reintroduction program has resulted in about 30 bald eagles living on the island.
|
|||||||||||||||||
|
Copyright © 2008 The Nature Conservancy
|
||||||||||||||||||
