Avian migration—the seasonal passage of birds—has undoubtedly fascinated man since he first looked skyward. Ducks, geese, swans, and many other birds follow ancient highways in the sky, each fall moving south to seek refuge in warmer climes and each spring miraculously reappearing on the breeding grounds as they emerge from the cold and snow of winter to herald the beginning of a new season.
We don’t know exactly how long waterfowl and shorebirds have traveled these migratory routes, but we do know the earliest recognizable waterfowl fossils date back some 40 to 50 million years. Adding to the intrigue, how birds navigate over the often thousands of miles on their migratory routes remains somewhat of a mystery. Scientists believe that a combination of factors are involved, including the position of the sun, changes in barometric pressure, geomagnetic force, landmarks, wind direction, and the position of the moon and stars.
No matter what the species or flyway, migration is a fascinating event. So come with us on a journey across North America from the Pacific to the Atlantic, the tundra to the tropics, and witness the ebb and flow of waterfowl and other wetland birds as they travel along these ancestral highways in the sky we call flyways.
Pacific Flyway
The Pacific Flyway stretches more than 4,000 miles from north to south and 1,000 miles west to east. In between are some of the most diverse habitats on the planet, including Arctic tundra, Boreal Forest, alpine meadows, vast grasslands, towering redwoods, coastal bays and estuaries, ephemeral and permanent wetlands, mighty rivers, and fiery hot deserts. The flyway begins on the tundra of Alaska, the Yukon, the Northwest Territories, and the Russian Far East. On the opposite end of the flyway, in Baja California, are bays where eelgrass grows in abundance and provides an important food source for wintering waterfowl.
Since the time of the Spanish explorers, human activities have modified the geography of the land. Even with the significant loss of wetland and upland areas due to expansion of agriculture and urbanization, the Pacific Flyway continues to provide breeding, migration, and wintering areas for an array of waterfowl and shorebirds, including some species that do not inhabit any other flyway.
Central Flyway
The Central Flyway is massive, covering more than a million square miles. Bounded on the west by the Rocky Mountains and spanning much of the Great Plains, it extends north to the farthest reaches of the Alaskan and Canadian Arctic and south into Mexico. Habitats include the tundra regions of the far north, the Boreal Forest, the Prairie Pothole Region, and the farm belt of the midwestern United States. Heading south, it sweeps through the high plains of Oklahoma and Texas, then on to the Texas Gulf Coast. In Mexico, both the Central Highlands in Chihuahua and Durango and the coastal marshes on the east coast in Tamaulipas and the Yucatán are included.
Unlike the Pacific Flyway’s several endemic species, the Central Flyway shares almost all its waterfowl with other flyways. While much of its native grasslands and wetlands have been altered, this vast region remains vitally important to continental populations of waterfowl and other migratory birds.
Mississippi Flyway
The Mississippi River runs like a gigantic artery through the flyway that bears its name. Traveling 2,300 miles from its source in the upper reaches of Minnesota to the Mississippi Delta, the river is a vital highway for ducks, geese, and swans moving to their wintering grounds in the fall and returning to their breeding grounds in the spring. Within the boundaries of the Mississippi Flyway lie five of the largest freshwater lakes on the planet—Lakes Superior, Michigan, Huron, Erie, and Ontario—as well as more wetlands than in any other flyway.
Mississippi Flyway breeding habitats encompass Arctic tundra, Boreal Forest, parklands, and eastern portions of the Prairie Pothole Region. Also within its boundaries are the tributaries and floodplains of the mighty Mississippi River and the coastal marshes of Louisiana. The flyway has no endemic species—none that remain exclusively within the flyway. But when it comes to the total number of wintering waterfowl, this flyway ranks above all the others and is the winter home to nearly half of North America’s mallards.
Atlantic Flyway
Reaching from the high Arctic tundra of Baffin Island in Nunavut to the warm, sunny isles of the Caribbean, the Atlantic Flyway extends more than 3,000 miles from north to south. Waterfowl breed from the Alaskan tundra and Canadian Arctic across the Boreal Forest and northern grasslands all the way to the Maritime Provinces. In the United States, west to east, the flyway extends roughly from the Appalachian Mountains to the Atlantic Ocean. Southward, the funnel-shaped migration corridor narrows to span an area from the eastern Great Lakes to the Atlantic Seaboard, then down the coast, eventually reaching Florida and the Caribbean Islands.
Within the flyway, former waterfowl havens have been dramatically altered by urban and industrial development. Fortunately, there are still places where coastal waterfowl habitats are largely intact and a variety of birds migrate and winter. Of the four flyways, the Atlantic supports the smallest total number of wintering waterfowl, but what it lacks in numbers it more than makes up for in diversity. The Atlantic Flyway has several subspecies of waterfowl that endemically breed, migrate, and winter only within its boundaries.
Available this fall, copies of Highways in the Sky can be ordered directly from the author at garykramer.net.
