The British Isles have a wide range of physical regions which encourages a tremendous diversity of birdlife. More than 200 species of birds breed or winter here. The most important reason why birds under. take migratory flights is simple. Winter cold reduces their food supply so much that they are in real danger of starvation. They need to seek warmer countries if they are to survive.
Birds become migratory only to ensure that more individuals of a species will survive, despite the risk of being blown off course during their travels, than if they stay to eke out a precarious living. If the risks of migration outweigh those of wintering, the species will be sedentary, but for some species, such as the lapsing and the song thrush, risks and disadvantages are so finely balanced that neither pattern dominates.
The time of departure of migratory birds is determined by the weathér, wind direction, and strength being more important to the birds than changes in temperature. Many birds regularly return to the same small area of territory and ringed birds returning have been recorded passing the same locality on the same date in consecutive years. Birds are able to navigate by means of the sun and stars, but how they do this has not yet been fully established.
What Is The Longest Bird Migration?
The Arctic Tern is the world’s champion long-distance migrant.