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Moving Day

More than one-third of the world's birds migrate. Migration is an instinct triggered by seasonal changes in weather and lack of food.

What causes the urge to migrate? Changes in the angle and amount of light rays may trigger migration. Low-pressure areas in late summer or autumn trigger a southward migration. High pressure in the spring encourages movement to the north. A lack of food in the autumn and winter may also send birds toward areas where food supplies are more readily available.

Birds migrate during the day or night. Daytime, or diurnal, migrators are generally larger birds like geese or hawks. These birds navigate by sight and have few if any predators. Many songbirds migrate in the safety of darkness. Their daylight hours are spent searching for food and resting for the next leg of their trip.

The ability of birds to migrate great distances and return to the same general area year after year is a subject which has fascinated people for centuries. Daytime migrators fly along broad air routes established by physical features such as major rivers, coastlines and mountains. The position of the stars and moon and the Earth's magnetic field are used by nigh time migrators.

Birds encounter many hazards during their migration. Nocturnal and low-flying migrants risk flying into manmade objects such as tall buildings, power lines, windows and wind turbines. Storms and bad weather during migration are a big hazard and can kill many migrant birds.