In most habitats there are seasons. They may be just a wet and dry season or they may be the seasons of winter, spring, summer and autumn. Each season brings different weather to the habitat. Many animals are adapted to survive in all the seasons in a habitat but some animals are not. They must move away when an unfavourable season approaches and return after it has gone. Animals that move away from habitat to avoid unfavourable weather are said to migrate and are called migrants. They travel to another habitat with more favourable weather and stay there until it is time to return.

Many kinds of birds migrate. They may migrate over short distances or long distances. Waders such as curlew and lapwing which nest and rear their young in the hills may migrate to a nearby estuary for the winter. Warblers which nest and rear their young in a woodland migrate to the woodlands of Africa for the winter.

A habitat may be visited by migrants in both summer and winter. An oak woodland is visited by warblers and flycatchers in the summer. They move to countries further south as winter approaches. In the winter the oak woodland is visited by redwings and fieldfares. These thrush-like birds move in from their summer habitats further north which have such severe winter weather that they could not survive there.

Some mammals migrate. For example some deer spend their summers high in the mountains but migrate to lower ground in the winter. In Africa the huge herds of gnu and zebra migrate across the savanna to find food as the seasons change.