In many places, the migrants awe birdwatchers with some of natures most spectacular sights. Waves of shorebirds, for example, descend on Delaware Bay in late May at the precise time when horseshoe crabs are busily laying eggs in the sand. The birds feast on this crab caviar, gaining strength to complete their amazing 4,000 to 6,000 mile journey from Latin American wintering areas to arctic breeding grounds.
A half a continent away in Nebraska, a half million sandhill cranes fatten up on the Platte River before heading north to breed. Residents celebrate the arrival of the huge flock each spring with the "Wings over the Platte" festival, sponsored in part by the Interior Departments U.S. Fish and Wildlife Service.
And visitors to the Malheur National Wildlife Refuge in Oregon see any of 300 species, including about 150 types of songbirds, ranging from thrushes to warblers to hummingbirds. Early in the spring, 50,000 snow and Ross geese and 12,000 sandhill cranes also stop over at this birding hotspot.
"A lot of people who enjoy the fall migration tend to forget the birds must fly north again in the spring -- and thats too bad," says Mike Hayden, Assistant Secretary of the Interior for Fish and Wildlife and Parks. "The vast majority of the 850 species of birds in North America are on the move this time of year. Its a great time to see them, especially since now they are in their colorful breeding plumage."
Aspiring birders dont have to travel far to catch a glimpse of the great migration: it is underway throughout the country. And there are 478 National Wildlife Refuges and many other protected areas managed by state and local governments and private conservation groups that serve as ideal places to watch the birds.
For example, more than 2 million people in the Minneapolis-St. Paul area can view 260 bird species at the Minnesota Valley National Wildlife Refuge, one of the Services half-dozen refuges located near large urban areas
And residents of Salt Lake City, Utah, can see more than a million shorebirds, 300,000 waterfowl, and tens of thousands of songbirds each spring within an hours drive at the Bear River Migratory Bird Refuge.
"This season affords people the opportunity to become more aware of the natural beauty and wildlife activity taking place so near to them," says John Turner, Director of the U.S. Fish and Wildlife Service. "Our refuges are treasures waiting to be discovered by the American public."
Bird migrations also present some intriguing scientific mysteries. How do birds know when to migrate in the spring? In the fall, the arrival of a cold front often triggers mass migrations. But how do shorebirds know when to leave South America each spring so they will arrive at Delaware Bay at the exact time the horseshoe crabs are laying their eggs?
Scientists are long on hypotheses but possess few solid answers. It could be the birds reproductive cycle that tells them to fly north to breed. Or it could be changes in the length of the day. Or temperature variations. Whatever the reason, many species of birds follow strict schedules, arriving at their northern breeding grounds on the same day or the same week every year.
And how do migrating birds navigate? The answer could be as simple as remembering familiar landmarks or as complicated as detecting differences in the earths thermal radiation or magnetism. As yet, no one knows for certain.
But most birds exhibit an uncanny knack for returning to the exact location where they nested the previous year, many to the same tree. The songbirds in a backyard this year, for example, may well be the same ones that nested there last year, or their offspring.
Perhaps the most confounding mystery of migration is how small birds such as the ruby-throated hummingbird, the arctic tern, and the lesser yellowlegs are able to fly hundreds and often thousands of miles.
The ruby-throated hummingbird, weighing well under an ounce, flies non-stop over the Gulf of Mexico on its way to wintering grounds in Latin America.
Scientists who have studied the birds physiology are confounded; there is seemingly no way such a tiny bird can store enough fat to fuel such a flight.
The three-ounce arctic tern flies a record 25,000 miles each year as it travels the globe from its wintering grounds in Antarctica to its nesting areas near the Arctic Circle and back. And lesser yellowlegs, which also weigh three ounces, have been know to fly more than 300 miles a day for nearly a week.
"As fragile as they may appear, these songbirds are ounce for ounce some of the most rugged critters around," says Turner. "It is amazing to think the tiny birds you see flirting around the shade trees in your backyard or in the park may have been in Venezuela last week."
But as durable as these birds are, there are disturbing signs that the spring migration isnt what it used to be. Populations of many of the more than 400 species that migrate to Mexico and South America have dropped sharply in the past two decades.
In the eastern United States, for example, the populations of 70 percent of these long-distance wanderers, referred to in biological parlance as neotropical migrants, have declined over the last decade, according to surveys by the U.S. Fish and Wildlife Service.
The cerulean warbler, for example, has declined at an average rate of over three percent per year for the last 25 years. Olive-sided flycatchers have fallen nearly 4 percent a year, and yellow billed cuckoos 1.5 percent per year over the past 25 years.
Biologists blame deforestation and other destruction of habitat both in North American breeding grounds and in Latin America wintering areas. As a result, the Service is a leading participant in "Partners In Flight," a cooperative effort among 12 Federal agencies and 19 private conservation organizations set up by the National Fish and Wildlife Foundation to study the reasons for these population declines and to promote more ecologically sensitive forestry practices. In addition, the program will encourage active conservation and management of habitats in national forests, parks, wildlife refuges, and on other public lands.
Some waterfowl populations also have declined. Widespread destruction of wetland habitat and years of low rainfall in the Midwest and Canada have driven breeding duck populations down nearly 20 percent below the long-term average in areas surveyed by U.S. and Canadian wildlife officials. Shorebirds, marsh-nesting birds, and other species dependent on these fragile wetlands have suffered as well.
The Service responded by working with the Canadian government to develop and implement the North American Waterfowl Management Plan with a goal of protecting, restoring or enhancing vital wetland habitats. More than 1.3 million acres have been conserved and 260 projects currently are underway.
Many of these projects are conceived and carried out at the local level by citizen groups, Federal and state natural resource agencies, conservation organizations, hunting clubs, and corporations.
"In a sense, the annual spring and fall migrations of birds serve as a barometer of our countrys overall environmental health," says Turner.
"Something troubling is going on out there. We are going to have to launch more cooperative efforts to protect bird habitats and take the other steps necessary to ensure future generations dont look up to see empty skies at migration time."
The U.S. Fish and Wildlife Service is the principal Federal agency responsible for conserving, protecting and enhancing fish, wildlife and plants and their habitats for the continuing benefit of the American people. The Service manages the 93-million-acre National Wildlife Refuge System which encompasses more than 530 national wildlife refuges, thousands of small wetlands and other special management areas. It also operates 66 national fish hatcheries, 64 fishery resource offices and 78 ecological services field stations. The agency enforces Federal wildlife laws, administers the Endangered Species Act, manages migratory bird populations, restores nationally significant fisheries, conserves and restores wildlife habitat such as wetlands, and helps foreign governments with their conservation efforts. It also oversees the Federal Aid program that distributes hundreds of millions of dollars in excise taxes on fishing and hunting equipment to state fish and wildlife agencies. For further information about the programs and activities of the U.S. Fish and Wildlife Service in the Great Lakes-Big Rivers Region, please visit our home page at: http://midwest.fws.gov
