Migratory animals and birds
It's not only birds that migrate. Animals of all shapes and sizes - from butterflies and eels to turtles and reindeer - are also on the move every year.
It's not just birds that migrate
Some animals, such as toads, may travel just a few hundred metres. Others, such as whales, may travel thousands of kilometres. All of them are moving for the same reason – to survive.
It took thousands of years for people to unlock the mysteries of migration. And there is still plenty that we don’t fully understand.
How do birds know where they’re going? How do they find their way? How do they survive the journey? Why do they come back?
The answers to these questions reveal some of the most amazing secrets of the animal world.
In the UK, pipistrelle bats migrate in autumn from the north to spend winter in the warmer south-west. Some even cross the channel to reach southern Europe. In North America, free-tailed bats migrate in huge numbers to hibernation sites in Texas and Mexico. More than 20 million may gather in a single cave.
Bats navigate by echolocation. This means they make high-pitched noises that bounce off objects around them to create an echo. This echo tells them where they are. Today scientists can use echolocation transmitters to hear these noises and discover exactly where bats are flying at night.
Weaker fliers, such as aphids, simply take off and trust the wind. Some spiders put up silken threads, like tiny parachutes, and drift for miles on the breeze.
However, these creatures do not return to the same spot and so their journey’s are not return migrations, like the ones birds make. The insects and spiders simply disperse to make sure that their population is not too crowded. In summer, the air can be thick with these tiny creatures, providing vital food for aerial feeders, such as swallows and swifts.
Some strongly flying insects do make return migrations, just like birds. The painted lady butterfly migrates each spring from North Africa to the UK – some getting as far north as Scotland. It returns in autumn to North Africa where it lays its eggs before dying. The next generation of painted ladies then sets off to the UK in spring.
The best known migrating butterfly is the monarch from North America. In autumn, as it gets colder, monarchs migrate south. Some travel more than 3,000km (1,800 miles), at an average speed of up to 50kph (30mph). They spend winter in Mexico and California, where hundreds of millions cluster on tree trunks in a few special forests. In spring, they mate, before flying north again to lay their eggs.