Mole, vole and toad migration
More about the short, but risky, trips made by smaller animals.
Moles and toads
Every spring, common toads make the short but risky trip from the woods where they spend winter to the ponds where they breed.
They travel at night to avoid predators, but many dangers lie in their path – including roads. Today some road signs warn motorists to look out for toads crossing.
Even moles have to migrate when their soil conditions change. If the soil becomes waterlogged during a wet spring, earthworms die. This deprives moles of their food – so they have to tunnel to new drier ground. If the soil dries out during a hot summer, moles find it hard to dig their tunnels and again they are forced to move on.
Arctic lemming migration
The Scandinavian lemming is simply a small member of the vole family that happens to migrate – like many other animals in the Arctic. The lemming just does it on a grander scale than most.
In good years with plenty of food, lemmings breed very fast. Each female has five to eight babies, and after only four weeks these babies can have litters of their own. So many young are born that the lemming population shoots up. This is called a population explosion.
As food supplies run low, some lemmings are forced to move out. They follow the most direct route and head for the highest point on the horizon. Unfortunately a lake sometimes gets in the way, and – though lemmings are good swimmers – some may drown. But not deliberately! Like all migrants, lemmings are simply moving to survive.