During this time of year, many birds have migrated for the winter. Some, like Partridges, don’t stray more than a kilometre from where they were born, but most birds – at least 4000 species – will migrate to seek new pastures that will see them through the colder months. There are several different types of migration that British birds follow, due to food availability or sometimes their own adaptations.
In an irruption migration, large numbers of birds that do not usually visit the UK arrive in a short space of time. In some years, the population grows too large for the food that is available in the birds’ usual territories, forcing them to relocate. Waxwings (Bombycilla garrulus) migrate in this way; some years we are fortunate enough to see large groups of these striking birds feeding on berries high in the trees, while other years there are none at all.
While many birds travel from north to south or east to west, some make shorter journeys from low to high altitudes and vice versa. Even though this migration may not be as physically demanding, there are still new challenges that come with a change in environment. In the UK, various larks, pipits and buntings are altitudinal migrants, including the Skylark (Alauda arvensis). As well as an altitudinal transition, many Skylarks will change habitat in winter. Having spent most of the year roaming farmland and heathland, coastal marshes become more favourable during the winter months.
Other migrations aren’t as a result of finding new feeding grounds but simply to stay safe. While all birds shed old feathers to grow new ones, species such as the Shelduck (Tadorna tadorna) lose all their flight feathers, making them very vulnerable to predation. In order to increase their chances of surviving while new feathers come through, Shelducks migrate to safer areas in late summer once the breeding season is over. A popular location for Shelducks is the island of Heligoland, situated in the North Sea. This allows the birds to moult with little disturbance.