'Migration is one of the great wonders of the natural world. This fascinating phenomenon takes many forms and is much more than a simple trip from A to B,' says Ben Hoare, author of the Museum book Animal Migration. Ben explains more below.
Is it the nomadic wandering of kangaroos in the Australian outback? Or a puffin’s fishing expeditions to find food for its chick? And what about the journey an earthworm makes to the surface of the soil and back again?
You could say that migration is a journey with a clear purpose from one area to another, often following a well-defined route to a familiar destination, and often at a specific season or time.
Flock of snow geese
But the reality is that there is no universally accepted definition of migration and it is not always easy to decide which are true migrations.
The problem is that animals carry out all kinds of different movements – short and long, seasonal and daily, regular and once-in-a-lifetime, highly predictable and seemingly random.
If one thing unites all migratory species, it is the fight to survive. Migration enables them to spend their life in two or more different areas, usually because lack of food makes it impossible to stay in the same place.
Other reasons animals migrate:
The classic idea of migration is birds flying north and south between separate summer and winter ranges, or whales travelling to faraway feeding or birthing grounds.
There are many others types of migration, including:
Members of the same species may follow a variety of different routes. And in some migrations, only one sex or part of a species’ population is involved.
Animals have evolved highly efficient direction-finding systems. This enables them to steer the right course over great distances, often with astonishing accuracy.
Monarch butterfly breaks the record for longest insect migration
Visual clues can play a central role. They include looking out for familiar geographical landmarks, and orientating by the Sun and stars. Patterns of polarised light in the sky are important, too.
Non-visual clues used in orientation include smells, tastes and sounds. Aquatic animals can analyse subtle changes in water quality and 'read' wave and current patterns. Most remarkable of all is the ability to orientate by sensing tiny variations in the Earth’s magnetic field.
Migration is not as dangerous as you might expect. It is a means of staying alive, after all. Migratory animals have evolved lots of ways to reduce the risks, such as: