Why do Birds Migrate?
Every spring and fall, we see birds migrating overhead, aiming towards their new homes. Why do they migrate, and how do they know where to go?
First, what is migration? Migration is when an entire group of animals move from one area to another area. A common migration in the US is of Canadian Geese, who fly south in late fall and back up north in March and April. These are readily seen by people on the ground, with their V formation and loud voices. However, many other birds migrate, including the swallows that go all the way from southern South America up to Northern Canada. Even longer, the Arctic tern goes around 18,000 miles on its route from the top to the bottom of the pole.
Most birds migrate in order to find food and proper breeding grounds. Birds tend to have a set environment they enjoy. Since the world doesn´t keep even temperatures in most parts of the world, birds have to move to stay happy. A robin which is thrilled pulling worms in the warmth of Connecticut in May will be miserable in January when there´s 3´ of snow on the ground.
Birds stock up on food before they begin their migration, since they expend a lot of energy on the way and might not find food well until they hit the end. They know when to migrate from a number of signals - the length of the days, the warmth of the environment, changes in weather, and so on. When the time seems right, the birds watch for good weather and strong winds, and head out!
While you can often look up during migration season and see the Vs of geese overhead, where are the other migrating birds? The answer is that they like to travel at night, when it´s safer. They sleep during the day at resting points, and then take off again in the evening.
Scientists are still studying how birds know where to go. Some birds orient themselves to the sun or moon, knowing in general that they have to go ´north´ or ´south´. Sometimes they can follow the coastline, knowing that if they stay along the coast and head north, they´ll hit a good spot that is warm and watery. Some even have a magnetic sensor so they can travel towards the poles, which helps them even when it´s overcast and dark.
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