Posted by: Dan | December 1, 2009

Quote of the Day: On the Wind

This excerpt comes from the Preface to Scott Weidensaul’s exceptional book Living on the Wind: Across the Hemisphere with Migratory Birds (Amazon US/UK). It sets the stage for the rest of the book while reflecting the wonder, the science, and the concerns of migratory birds.

The footnotes towards the end are mine.


Living on the Wind, by Scott Weidensaul

Across the Hemisphere with Migratory Birds


At whatever moment you read these words, day or night, there are birds aloft in the skies of the Western Hemisphere, migrating.

If it is spring or fall, the great pivot points of the year, then the continents are swarming with billions of traveling birds — a flood so great that even the most ignorant and unobservant notice, if nothing else, the skeins of geese and flocks of robins.

But the migration’s breadth goes far beyond those obvious watersheds, shifting endlessly across distance and season. In the middle of July, Hudsonian godwits lift off from the iceberg-choked shorts of the Beaufort Sea, heading southeast along the northern rim of Canada to Labrador, then vaulting south in a nonstop flight to Venezuela. In the snow squalls of December, goshawks and golden eagles fly south along the ridges of the Appalachians, over oak trees that rattle their last stiff, dead leaves at the wind. Even within the tropics, a land where migration would seem unnecessary, birds move with the seasonal rains and droughts across hundreds of miles, following the blossoming of flowers or the ripening of fruit.

More below the fold…

They don’t all follow the expected course, nor do they always travel by wing. With the fist winter snows, blue grouse leave the more temperate foothills of the Western mountains and migrate — on foot, no less — into the bitter, wind-drifted high country, searching for conifer needles to eat.

A very few travel even beyond the bounds of the hemisphere. Tiny songbirds from Alaska leap west across the Bering Sea to the Philippines, and others from eastern Canada cross the North Atlantic to Europe and Central Africa. Short-tailed albatrosses from Japan glide down the coast of Washington in summer on wings as fragile as a whisper; in those waters the albatrosses pass shearwaters from New Zealand and storm-petrels from Antarctica and the Galapagos.

Even the darkness moves with the passage of birds. On soft spring midnights, the air is alive with the flight notes of unseen warblers and vireos, thrushes and orioles, sparrows and tanagers, filtering down through the moonlight like the voices of stars.

Bird migration is the one truly unifying natural phenomenon in the world, stitching the continents together in a way that even the great weather systems, which roar out from the poles but fizzle at the equator, fail to do. It is an enormously complex subject, perhaps the most compelling drama in all of natural history.

That such delicate creatures undertake these epic journeys defies belief. Only recently have scientists discovered that some shorebirds apparently fly nonstop from the southern tip of South America to the coast of New Jersey, a journey of ten days — 240 hours of uninterrupted flight. Even more remarkable are the four-ounce Arctic terns that leave the northern fringe of the continent each autumn, flying east across the Atlantic to Europe. They push south along the bulge of Africa, recross the Atlantic to the edge of South America, and spend the winter months moving east off Antarctica. In spring they reverse course, moving up southern Africa and lancing back to Canada — a figure eight inscribed on half the globe, a track that returns them, often as not, to precisely the same sheltered nook where they nested the summer before.

Even scientists have little grasp of the numbers of birds involved in this seasonal ebb and flow. In spring, hordes of warblers, tanagers, vireos, and other tropical migrants cross the Gulf of Mexico each night, arriving on the U.S. coast at a rate that may exceed a hundred thousand songbirds per mile of shoreline, with tens of millions making landfall each day. On a single autumn night several years ago, radar on Cape Cod indicated that 12 million songbirds passed overhead. And on the narrow coastal plain of Veracruz, Mexico, biologists discovered only recently one of the greatest raptor migrations in the world, where nearly a million hawks have been counted in a single day. In all, scientists guess, more than 5 billion birds annually weave this incredible tapestry across the hemisphere.

Because they travel such extraordinary distances, often with differing requirements for food and shelter along the way, migratory birds pose one of the stickiest conservation challenges in the world. In the past, preservation programs focused on saving breeding areas, but experts now realize they must also save wintering grounds and migratory stopovers if this global web isn’t to unravel.

There are serious signs of fraying. Birders have warned for years that songbird numbers were dropping, and now scientists have hard evidence that some beloved species, like wood thrushes and cerulean warblers(1), have declined by more than 75 percent in the past quarter century. Entire communities of birds, like those that nest in open grassland, are in freefall. In the past, the dangers to birds were mostly direct persecution, and the remedy was legal. The Migratory Bird Treaty Act(2), passed in 1918 and amended several times since, is the cornerstone of federal protection, levying harsh fines and jail time for killing all but a relatively few game birds. The law grew out of a time when songbirds and shorebirds were still routinely shot for the dinner table and terns and egrets were slaughtered so their feathers could decorate hats.

Today, however, the biggest threats to migratory birds do not come from the barrel of a gun, nor are they easily cured by passing laws(3). They arise from habitat loss and the wholesale environmental changes we have imposed on the natural world. Laws like the federal Endangered Species Act provide last-ditch support for almost-extinct birds, but conservationists now realize the smartest approach is to recognize the trouble early and try to stabilize populations while they are still relatively common. This recognition, coupled with an impending sense of crisis, has sparked an unprecedented international conservation effort, probably the largest and most ambitious in history, involving virtually every country in North, Central, and South America in research, education, and habitat protection. By way of example, one such multinational approach is the Western Hemisphere Shorebird Reserve Network, which has identified (and in some cases prompted the preservation of) 4 million acres of wetlands between Argentina and Alaska, upon which more than 30 million migratory shorebirds depend.


Notes:

1. Weidensaul and his books are very focused on birds of the Western Hemisphere, which is of course what he knows best. For readers in the Eastern Hemisphere, you may want to replace Wood Thrush and Cerulean Warbler as common species experiencing drastic declines in the past quarter century with Grey Partridge, Meadow Pipit, Eurasian Linnet, Rustic Bunting, and Woodchat Shrike (Pan-European Common Bird Monitoring Scheme Report, 2008). These five species are among those that have declined between 49% to 72% in Europe since 1980.

2. For Europe, the directive most closely corresponding to the Endangered Species Act is the European Community’s Directive 79/409/EEC on the conservation of wild birds.

3. While this is still true in Europe and even southern Europe where existing laws are widely disregarded even by law enforcement, there are still a great many birds slaughtered in Cyprus, Malta, and other countries.


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