The blackpoll warbler is a tiny migratory songbird that spends the summer in northern North America and the winter in South America. In autumn, it builds up energy reserves before making an extraordinary nonstop flight over the Atlantic Ocean that can last up to three days.
"In accordance with their inherited calendars, birds get an urge to move. When migratory birds are held in captivity, they hop about, flutter their wings and flit from perch to perch just as birds of the same species are migrating in the wild. The caged birds ‘know’ they should be travelling too. This migratory restlessness, or Zugunruhe, was first described by Johann Andreas Naumann…[who] interpreted Zugunruhe to be an expression of the migratory instinct in birds."
--William Fiennes, ‘The Snow Geese’
Lots of animals, from whales to wildebeest, make long annual migrations. But birds do it in the most spectacular fashion. They move farther, faster, and in greater numbers than any other animals. On a single autumn night with favorable winds, there can be more than 1 billion birds in the air over the United States alone.
Some birds travel tremendous distances: Arctic Terns and Sooty Shearwaters fly more than 50,000 km (31,000 miles) in a single year. Bar-tailed Godwits depart Alaska at the end of summer and fly nonstop for 8 days over the Pacific Ocean, landing in New Zealand. Even little songbirds and tiny hummingbirds routinely fly 1,100 km (700 miles) across the Gulf of Mexico each year. In all, more than 300 North American bird species are long-distance migrants.
Although some birds migrate during daytime, including raptors, waterfowl, and swallows, most birds migrate at night, when atmospheric conditions are calmer and there are fewer predators about. So how do birds travel such long distances, in the dark, and find their way to the exact same patch of wintering or breeding habitat each year?
Cornell Lab of Ornithology, “The Basics of Bird Migration: How, Why, When, and Where,” All About Birds. Read the article.
Birds typically migrate to take advantage of these three resources:
Cornell Lab of Ornithology, “The Basics of Bird Migration: How, Why, When, and Where,” All About Birds. Read the article.
- Food. Birds that nest in the Northern Hemisphere tend to migrate northward in the spring to take advantage of a few months of plenty, fed by burgeoning insect populations and budding plants.
- Breeding Sites. The vast boreal forests and open tundra of the Arctic provide huge expanses for shorebirds and songbirds to nest in, compared with the crowded forests of the tropics—making it worth the long journey.
- Daylight. Near the equator, daytime is about 12 hours long all year. By traveling to nearer the poles, birds can get much longer daylight, just when they need it most for raising their young. The extra daylight also fuels the abundant plant, plankton, and insect booms that create such a plentiful food supply.
Migrating birds can cover thousands of miles each year, often traveling the same course and arriving in the same patch of habitat year after year. Juvenile birds often migrate on their own, without any adults to show them the way, just a couple of months after they hatched. Somehow they can find their winter home despite never having seen it before.
Birds achieve such amazing navigational feats thanks to a combination of powerful senses. Cues they use include the position of the sun, and of sunset, the rotation of the stars, the Earth’s magnetic field, landmarks such as ridgelines and river valleys, and even their sense of smell.
Cornell Lab of Ornithology, “The Basics of Bird Migration: How, Why, When, and Where,” All About Birds. Read the article.
Embarking on a thousand-mile journey is dangerous and demanding. Birds face the tests of extreme physical exertion, lack of food along the way, unpredictable storms and headwinds, unfamiliar stopover habitat, predators, and the demands of navigating the correct course.
Increasingly, migrating birds also face human-made threats, particularly artificial lights and collision risks from windows, communication towers, and tall buildings.
Cornell Lab of Ornithology, “The Basics of Bird Migration: How, Why, When, and Where,” All About Birds. Read the article.