Thousands of snowy owls have descended upon the northern United States this winter. The owls usually live on the Arctic tundra in Canada. Some migrate south in the winter, but 2012 has been remarkable for the great numbers of owls that have come south. Such a large migration is known as an irruption. The owls have also spread farther than usual, appearing from the Atlantic coast to the Pacific and as far south as Kansas. One owl even reached Hawaii, where authorities shot it out of concern it would interfere with aircraft. Scientists are not certain why the owls have migrated in such numbers. However, many animals in northern regions follow a boom-and-bust population cycle. For example, lemmings quickly grow in numbers when there is abundant vegetation. A boom in the population of lemmings provides abundant food for snowy owls. However, the lemmings soon eat much of the available food, and their numbers plunge. Then, there are not enough lemmings to support the large number of snowy owls. These conditions may cause snowy owls to fly farther south than usual in search of alternate food sources.
Why Do Birds Migrate?
Many kinds of birds travel great distances to find food or to avoid harsh weather brought by changing seasons. During migration, birds may fly hours or even days without stopping to reach their new home.
In many parts of the world, food is in short supply during certain seasons. Insects do not remain active during harsh winters. As a result, birds that feed on insects would starve if they stayed in an area with harsh winters. Instead, these birds migrate to areas where insects remain available. Birds may also migrate in search of food during the wet and dry seasons in the tropics. Many birds travel to warmer climates in the fall. They return in the spring, when the weather warms up again. Millions of birds gather in the Arctic as the weather warms there. In the fall, these birds migrate south, before the weather turns cold.
How birds migrate
Most migrating birds head either north or south in response to changing seasons. Some species of birds fly in small flocks. Others fly in flocks with many thousands of birds. Most birds migrate along the same routes (paths) each year. Some birds migrate a fairly short distance. But others travel for weeks or even months. The Arctic tern flies all the way from the Arctic to Antarctica, only to return a few months later. Through these migrations, it travels about 22,000 miles (35,400 kilometers) in less than a year.
The blackpoll warbler is a North American bird that makes one of the longest continuous migrations. It flies nonstop nearly 2,500 miles (4,000 kilometers) to its winter home in South America. The journey takes about 90 hours.
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