Bird Migration

Think of people who head to the beach to escape summer heat, or fly south to somewhere warm in the dead of winter. Migratory birds do much the same thing. They are seasonal travelers who fly thousands of kilometers to find the best place to live.

Many people assume birds migrate simply to escape the cold. But the real biggest reason is to secure plenty of food for raising their chicks. In spring and summer, the north has long days, and food like insects and seeds becomes very abundant.

When winter approaches, the northern ground freezes over and food becomes impossible to find. So the birds fly south, where it's warmer and food is still available, and wait out the winter there. Migration is a tough journey, but it is nature's brilliant survival strategy for giving the species the best chance of surviving.

How do migratory birds cross open oceans and unfamiliar continents without getting lost, and still arrive at exactly the right spot? Inside their bodies is a built-in navigation system that beats any high-tech car's GPS.

During the day, they set their direction by the position of the sun. Birds that migrate at night look for the point in the night sky that the stars appear to circle around (near the North Star) to tell which way is north. They even remember the look of landmarks like coastlines and huge mountain ranges and use them as guides.

The most amazing part is their ability to read an invisible force of the Earth. With a sense that detects Earth's magnetic field, birds read the angle at which the magnetic field lines meet the ground, which tells them which way is toward the pole and which is toward the equator. Many studies link this sense to light-sensitive proteins in the eyes, but scientists are still working out exactly how it works.

Flying such long distances takes enormous stamina. So before migration season, birds eat far more than usual and build up fat. Depending on the species, their body weight can nearly double. That fat works like jet fuel.

To be more precise, long-winged birds like geese and ibises fly in a V-shaped formation. The swirling air that forms at the wingtip of the bird in front gives the birds behind an extra lift. Flying this way lets them save a lot of flight energy compared with flying alone.

In recent years, bright artificial city lights and climate change have been causing serious problems, such as birds losing their way or missing their migration timing. Bird migration is more than a simple bird trip. It is a great circle of nature that shows how healthily the whole planet's ecosystem is connected.