Winter can be a hard time for animals. It’s cold, and it’s hard to find food. Some animals, like bats and bears, solve this problem by sleeping through the winter. Other animals, especially birds, solve the problem by migration – moving to somewhere warm for the winter, then coming back in the spring.
If you live in Canada, you’ve probably seen Canada geese flying south in V-shaped flocks to spend the winter in the southern United States. In Japan, many seabirds fly to Australia for the winter. Many European birds spend the winter in central Africa. Maybe some people in your family like to fly south for the winter too!
If you’ve ever gone on a long road trip with your family, you know that it’s something you have to plan and prepare for. Birds prepare for migration by eating a lot of food, so that they have the fuel to fly a long distance – kind of like gassing up the car.
Another important part of a road trip is rest stops. You need to stop every so often to eat something, go to the bathroom, and stretch your legs. Similarly, birds can’t make the whole trip in one go. They need to make a couple of stops along the way. So it’s important that there are still wild areas along a migration route, not just cities, so that birds can stop for a rest and a snack.
How do birds know which way to go? They can sense the earth’s magnetic field. The planet earth is a big magnet. You can make a device called a compass that uses a small magnet to point at the earth’s north pole.
- Metal needle
- Drinking glass
Rub the end of the needle against the magnet about thirty times. Make sure that it’s always the same side of the magnet, and that you’re always rubbing it in the same direction. This will turn the needle itself into a small magnet.
Tie a short piece of thread to the middle of the needle and tie the other end to the middle of the pencil. Lay the pencil across the top of the drinking glass, letting the needle hang down into the glass.
Now that the needle is able to spin freely, it should point north! Even when you turn the glass and the pencil, the needle should still point in the same direction. Check on a map to see if it worked.
Birds have something similar inside their bodies (new research suggests that it’s a protein in their eyes), so they always know which way is north.
If you don’t have time to make this, your smartphone probably has a compass in it too.
(Compass activity modified from here.)
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