|
June 7, 2005 was moving day for seven American bald eagles. Only eight weeks old but nearly full-grown in size, the young eagles were relocated from their nursery at the San Francisco Zoo to their adult stomping grounds — the valleys, hills and coastline of Santa Cruz Island.
The largest of the eight Channel Islands, Santa Cruz Island harbors more than 1,000 species of plants and animals, including twelve species that are found nowhere else in the world. Scientists are hopeful that Santa Cruz Island, once a stronghold for the American bald eagle,will again be home to these majestic birds.
First Flights
Since moving to Santa Cruz Island, the seven young eagles, along with three more transferred a few weeks later, have been living in "hack towers" — large nesting boxes about ten feet off the ground where the birds test their wings and adjust to the island's breezes. Biologists who live on the island feed the birds two times a day, and cameras inside the pens allow constant watch. In early July, after a month of growing the feathers necessary for flight, the birds will be encouraged to fly on their own.
"We'll just open the doors and they'll fly when they're feeling comfortable," says Dr. Peter Sharpe, a biologist with the Institute for Wildlife Studies.
To track the birds once they've taken flight, biologists tag each with a number and a Global Positioning System (GPS). The size of a small walkie-talkie strapped on like a backpack, the GPS units allow Sharpe and his team to monitor the birds' exact locations and travels.
History
Bald eagles historically resided on all of the Channel Islands off the coast of southern California, but by the early 1960s they had disappeared.
"We don't think any chicks were produced after the late 1940s," says Sharpe.
The primary cause for this decline was DDT. Between the 1940s and 1970s, chemical companies dumped millions of pounds of pesticides into the ocean off the coast of Los Angeles. High concentrations of DDT in fish and other food sources led to a build-up of the chemical in the birds' reproductive systems. As a result, bald eagles laid very thin-shelled eggs that broke before the chicks could fully develop.
"When the adult eagles died of old age, there were no young birds to re-establish the population, and bald eagles just disappeared," says Sharpe.
The use of DDT was banned in the United States in 1972, but chemical deposits on the ocean floor continue to build up in marine life. Settlement of a lawsuit with the chemical companies yielded funding for restoration efforts on the Channel Islands.
Since 2002, biologists have relocated approximately a dozen bald eagle chicks each year to Santa Cruz Island. But they won't know if the first eagles released can successfully reproduce for another year or two, when the eagles reach sexual maturity. While similar reintroduction efforts in the Southern Channel Islands were recently halted after a 20-year effort, scientists are optimistic that bald eagles will fare better on Santa Cruz Island, which is farther north from the contamination site.
Bald Eagles and the Island Ecosystem
While only time will tell if the eagles are able to reproduce, their importance to the island ecosystem is unquestionable.
"It's like if you have a large card house and pull out some of the key cards at the foundation. The whole system collapses," says Dr. Lotus Vermeer, the Conservancy's Santa Cruz Island project director.
The absence of territorial bald eagles on Santa Cruz Island paved the way for golden eagles to colonize the island in the early 1990s. Lured to the island by the abundance of non-native feral pigs, golden eagles have also preyed upon the island fox, which now hovers near extinction. (Read more about the Conservancy's multi-partner Island Fox Recovery Project here.)
"Our hope is that once the bald eagles mature and mate, they'll defend their territory and deter the golden eagles from returning," says Vermeer.
In the meantime, biologists eagerly await the first flights of these ten juvenile bald eagles.
|
