In an effort to bring more awareness to bird migration, considering spring migration has just passed, I want to share with you this informative essay from my book, Bringing Back the Birds, in partnership with American Bird Conservancy. Kenn and Kimberly Kaufman are field guide authors, naturalists, educators and conservationists.
On a clear, crisp night in late September, we stood on the outskirts of a small city in northwest Ohio. We looked to the sky, but we were not stargazing – the stars were the backdrop for a performance we hoped to attend. The weather forecast had indicated that this night would provide the right conditions, and long after sunset, the action began.
Soft notes began to drift down from above – a few at first, eventually swelling to a chorus. Light lisps and chips of sparrows and warblers were interspersed with stronger whistles of Swainson’s Thrushes and nasal notes of Gray-cheeked Thrushes. In swift, sure flight toward the south, on the grandest of stages, songbirds were performing the ancient act of migration.
Every spring and fall, massive numbers of birds – billions of birds – take to the sky for epic journeys. Some travel thousands of miles, vaulting from one continent to another, then returning with pinpoint accuracy to a breeding territory or wintering site that they might have left eight months earlier. This immense parade of small travelers may pass unnoticed by most people. But for those who are aware, it’s the most astonishing phenomenon in the natural world.
Many kinds of creatures, from whales to butterflies, undertake regular seasonal travels. But such migrations are far more common among birds than in any other group. Of the bird species found regularly in North America, for example, more than 80 percent are at least partially migratory.
But why? Such travels can be more hazardous than staying put, so why do so many birds do it?
With the mobility of flight, birds can move around the earth to take advantage of resources that are available only at certain seasons. Consider what happens in one extreme environment: the tundra of northern Canada and Alaska. In midwinter – with perpetual darkness, deep snow, and temperatures well below zero – very few birds can survive there. However, summer brings an explosion of life as ponds thaw, flowers burst into bloom, rodents scurry over the tundra, and hordes of insects emerge. Food is so abundant, even if only briefly, that it becomes worthwhile for birds to travel there to nest and raise their young. Thus, huge numbers of birds – ducks, geese, plovers, sandpipers, owls, sparrows, buntings and more – come pouring into Alaska from their wintering sites all over the Western Hemisphere. The advantages of the food bonanza on the tundra outweigh the risks of the long journeys they must make to get there.
Other habitats are less extreme, but they also go through seasonal shifts in availability of resources. The vast boreal forests of Canada and Alaska support a few kinds of insect-eating birds, such as chickadees and woodpeckers, during the winter, but in summer those same forests play host to a dazzling variety of warblers, vireos, flycatchers, thrushes and other birds that come north from the tropics. Ponds on the northern prairies, frozen hard in January, teem with ducks, grebes and phalaropes in June.
These seasonal changes aren’t limited to places that freeze over. Southern Florida is a winter destination for many northern breeders, but some local nesting birds – such as Swallow-tailed Kites and Gray Kingbirds – leave Florida entirely in winter to go farther south. Even in tropical regions of Mexico, some summer residents, including the Sulphur-bellied Flycatcher and Yellow-green Vireo, depart in fall to fly to South America. And the overall pattern is repeated, in reverse, in the Southern Hemisphere. Many songbirds that breed in far southern Argentina or Chile fly north to escape the austral winter, moving to Brazil or the northern rim of South America, some even into Central America.
No two bird species have exactly the same migratory patterns. The routes of their travels, if we could plot them all in a map, would look like an incredibly complex web, with threads running in all directions to connect practically all points on earth. In our region of northwestern Ohio, on a day when birds are moving north, we might see birds coming from a wide variety of wintering areas: Blackburnian Warblers coming from the Andes of Ecuador, Eastern Kingbirds from the Amazon basin in Brazil, Wilson’s Warblers from Mexico, Black-throated Blue Warblers from Jamaica, Wood Thrushes from Costa Rica, American Golden-Plovers from near the southern tip of South America in Argentina. They pause with us briefly before continuing northward to nesting sites scattered all across Canada and Alaska.
These birds forge strong connections between us and the rest of the Western Hemisphere. Their journeys are the threads that connect every bit of land and water in the Americas.
The scale and scope of the phenomenon – billions of birds, thousands of miles – are almost too much to comprehend. Even when we break it down to the level of the individual migrants, some of their travels are beyond belief.
Arctic terns, for example, spend the summer raising their young along northern coasts and tundra, including many regions far north of the Arctic Circle. As autumn approaches, they fly south . . . way south. Looping across oceans and skirting continents, they wind up among the pack ice along the edge of Antarctica, a world away. Some individuals tracked with tiny geo-locators have been shown to cover an annual round-trip distance of more than 96,000 kilometers (almost 60,000 miles).
These impressive flights are rivaled by migrants coming the opposite direction, nesting in the south and migrating north. Far off the Atlantic coast of the United States, Wilson’s Storm-Petrels are among the most numerous birds in summer. These tiny black seabirds, fluttering over the waves like errant swallows, may not look like strong flyers, but they are: their closest nesting sites are more than 11,000 kilometers (7000 miles) away, around the southern tip of South America and islands around Antarctica. Off the coast of California, it is possible to see thousands of Sooty Shearwaters in a day, and every one of those birds has migrated north from nesting sites on islands deep in the Southern Hemisphere, around Australia, New Zealand, and southern South America.
When seabirds such as storm-petrels or shearwaters are migrating over the ocean, they can take breaks by stopping to rest on the ocean’s surface. That isn’t an option for land birds that undertake long flights across the water.
For example, Bar-tailed Godwits – big cinnamon-colored sandpipers – nest across northern Europe and Asia into western Alaska. Those that spend the summer in Alaska migrate all the way to New Zealand for the winter. Recent studies have confirmed that they can make this journey in one non-stop flight, taking a diagonal track southwest across the Pacific for more than 11,000 kilometers (7000 miles), flying continuously for more than eight days! To prepare for this marathon, godwits feast before they leave Alaska, gorging to put on fat for fuel. To maximize the fat they can carry without increasing their weight too much, they partially absorb some of their own internal organs such as the liver, kidneys, and alimentary tract, regrowing these organs after they reach New Zealand. No extreme athlete among humans can go to such lengths.
As amazing as the godwits’ flight is, we are more impressed by the exploits of the Blackpoll Warbler. This tiny songbird – it would take more than two dozen of them to equal the bulk of one godwit – has its own long overwater flight, every bit as heroic given the warbler’s size.
Blackpoll Warblers spend the summer in the boreal forest, from northern New England all across Canada and Alaska. Those from the far western end of the breeding range don’t fly south in fall; instead, they move east across the continent, heading for the Atlantic coast. On the eastern seaboard, anywhere between Canada’s Maritime Provinces and the middle Atlantic states, they spend days feeding and fattening up, almost doubling their weight. Then they launch out over the water, aiming southeast, toward the northern coast of South America. They may fly for as much as eighty hours – four nights and three days – traveling more than 3200 kilometers (2000 miles) over the open Atlantic before they touch down again.
It’s astonishing to think of a young Blackpoll Warbler making this trip for the first time. Just a few months after it hatches, guided by pure instinct, it makes its way to the eastern edge of North America in autumn. Then it waits for the right night: after it has built up its fuel reserves, after a weather front has passed, bringing clear skies and northwest winds. Just after sunset the tiny bird takes off and climbs into the sky, arrowing away toward the southeast, into the unknown, on a journey that we cannot follow even in our imaginations.
When Blackpolls arrive in Ohio in spring, making their way north again, we’re reminded that each one we see is a survivor of this inconceivable marathon.
The ability to migrate, to take advantage of resources at different places and seasons, is a great benefit to a species as a whole. But for the individuals involved, it brings great risks. When a bird is on its own territory in summer or winter, it knows the local turf: where to find food and shelter, how to avoid danger. Stopping over in unfamiliar places during migration, it knows none of these details. And every flight between stopovers brings the chance of weather conditions that can be fatal, especially if storms catch the birds over open water.
Migration has always been risky, but today it is becoming even more so. Loss of habitat is a continuing threat at every stage of a bird’s life. A bird may complete a long journey only to find that its breeding or wintering habitat has been destroyed. Even en route during migration, tracts of good stopover habitat are essential for survival. If birds can’t rest and refuel at these sites, they may not make it to their destinations at all. Every year, as areas of breeding, wintering, or stopover habitat are removed or fragmented, the challenges for migrating birds become greater.
Humans are also adding more and more hazards to the obstacle courses of migration. Many night-flying migrants are killed when they collide with towers or tall buildings; the proliferation of wind turbines will multiply the threat, especially if those turbines are placed close to important stopover habitats. Staggering numbers of birds are killed by free-ranging house cats, unnatural predators that have no place in American ecosystems.
Even where habitat remains untouched, shifts in climate may add to the challenges. After surviving drier winters in some areas of the tropics, for example, migratory birds may start north later than normal or in poor condition, and those effects can carry over into the breeding season, reducing the chances that those individuals will succeed in raising young. And as extreme weather events become more intense and more frequent, they’re likely to play havoc with the attempted travels of many species.
For all of these reasons, the protection of migratory birds has become one of the most challenging areas of conservation work. Even to protect the birds that we see passing through our own region of Ohio, we can’t focus on just the local scene. We need thoughtful, strategic action throughout the Americas to protect migratory birds throughout their entire life cycle.
Such action depends on public support. Unfortunately, most people are barely aware of the issue. True, there are a few places where big birds pass in big numbers in daylight, making migration impossible to ignore: hawks streaming down the coast of Veracruz, Mexico, for example, or cranes gathering the Platte river in the Midwest. But most migrants pass unnoticed.
On that September night in Ohio, as flight calls of migrating songbirds drifted down from overhead, it occurred to us that no one else was listening. In a city of almost fifteen thousand people, we were likely the only ones aware of this passage of birds, this astonishing act of nature, playing out in the night sky. But that thought didn’t give us any smug satisfaction; instead, we wanted to change that equation.
We must do all we can to help connect people with the wonder of birds. Of course birds play essential roles in the natural world – providing ecosystem services, to use the technical term. For that reason alone, their conservation is necessary. But they are also beautiful, endlessly fascinating, and intensely alive. An awareness of birds enhances quality of life in myriad ways, bringing more joy into the world.
That’s why we’re determined to keep telling the stories of these remarkable little travelers. If enough people are aware, if enough people care, then we can ensure that future generations will have the opportunity to witness the ancient and awesome pageant of migration, to know the wonder of birds in their lives.