One minute they are there, the next they are gone... swallows and house martins are a familiar sight zipping over our garden throughout summer but suddenly one day they apparently disappear. They are just two of many bird species found in Britain that undertake migrations. As the nights draw in and air temperatures decrease, there is a ‘changing of the guard’ in the UK. Some of these species leave to winter in sunnier climes whilst others are arriving to escape the cold in their summer home countries.
Our summer visitors include swifts, house martins, swallows and warblers. These birds leave in autumn, heading south often to parts of Africa where temperatures are warmer and food more plentiful during our winter months. They return again in spring to raise young when competition for food in Africa gets high and there are longer daylight hours for foraging in the Northern hemisphere. Our winter visitors tend to be species returning from their summer breeding grounds in Scandinavia and Northern Europe when food supplies become covered in snow and/or ice. These include members of the thrush family, geese and other wetland and shore birds.
Some species undergo their seasonal migrations in one non-stop flight. For example certain warbler species gorge themselves on food at the end of summer, doubling their body weight before undertaking a 4 to 5 day flight south. In contrast other species will stop off regularly during their journey to roost and feed. For example swallows can take several months to complete their migration. There are several species found periodically in the UK which are themselves using the British Isles as a stop-off on their migratory path.
In addition to these mass migrations spanning thousands of miles, there are many smaller migratory activities of birds within the UK at this time of year. For example thrushes tend to move from northern Britain southwards to avoid the harshest weather conditions. Many tits and wrens have been found to relocate from the open countryside to the more sheltered habitats of urban areas during winter months.
There have been bird ringing schemes in place in Britain and Ireland since 1909 which have enabled ornithologists and scientists to map the movements of hundreds of bird species and make some startling discoveries. In 2003 a Manx Shearwater was captured that had previously been caught and ringed in 1957. Experts suggest that the amazing creature must have flown over 5 million miles within those 46 years! The Migration Atlas brings together much of this work over the last 100 years, providing comprehensive accounts and illustrations of almost 200 species found to visit the British Isles.
