Air Date: Week of March 24, 2000

This week, facts about migratory birds.

Transcript

CURWOOD: It's Living on Earth. I'm Steve Curwood

(Music up and under: "Come Fly With Me")

CURWOOD: As the days grow longer with the arrival of spring, the skies of the Northern Hemisphere are a-jabber with migrating birds heading north from their wintering grounds. For some birds the migration from winter to summer habitat is as simple as moving a few miles up a mountainside. For others, the journey can be thousands of miles from the tropics, or even further. One of the champion long-distance fliers is the Arctic tern, which travels over 10,000 miles each spring from the Antarctic to the Arctic Circle. No less spectacular is the pilgrimage of the ruby-throated hummingbird. It weighs only one tenth of an ounce, yet crosses the Gulf of Mexico in one 500-mile-long flight. Then there's the rock-hopper penguin, which can't fly at all, but migrates anyway by swimming hundreds of miles through the ocean. For many birds, the seasonal journey is more challenging than it used to be. A whole range of environmental pressures, from changing temperatures to shrinking habitats, is reducing both the food supply and places to roost along the way. Migrating birds are often squeezed into small areas, increasing the competition for food and the risk of disease. And why do they fly? The urge is probably triggered by changes in the amount of daylight and the weather. Each species uses its own special map to find its way, including stars, the earth's magnetic field, odors, landmarks, even seasonal breezes. And just as birds use natural cues to mark the rhythms of their lives, humans use migrating birds to mark the rhythms of our lives. When we see the flocks heading south again, we'll know that winter can't be far behind. And for this week, that's the Living on Earth Almanac.