Is that my Robin?

An overview of bird migration.

Bird Migration is a tricky topic to puzzle out. Spring is a good time to get your head round this with summer migrants arriving and winter visitors leaving. Westhay and Catcott are ideal sites to observe this in action. Here are some broad outlines about the topic followed by some Did-You-Knows.

Of Britain’s 300 most common birds, about 100 can be called migrants. These can be grouped like this:

• Winter Visitors (about 30) such as Fieldfare, Barnacle Goose, Brambling and Turnstone.
• Summer Visitors (about 50) such as Nightingale, Common Tern, Sand Martin and Hobby.
• Passage Migrants (about 20) such as Little Stint, Great Grey Shrike, Curlew Sandpiper and Wryneck.
In general, summer visitors arrive from the south (mainly southern Europe and Africa), and winter visitors from the north (the Arctic and Scandinavia). There are also partial migrants where only some individuals of the species migrate.

Why migrate?

Birds migrate to take advantage of longer days, more food, fewer threats and less competition. Arctic Terns travel from the Arctic to the Antarctic and back, up to 40,000 miles each year, to make use of the daylight and the abundance of fish.

With partial migrants, some remain where they are after breeding and some migrate. Experiments with Blackcaps and Stonechats have shown that within a few generations, groups of once-migratory birds can alter their behaviour to staying in one place all year round.

Did You Know?

• The Robin in your garden in winter may not be the same bird as the one you see in summer. Some Robins, Blackbirds and Song Thrushes migrate.

• Young Common Swifts set off on migration to southern Africa before their parents and may spend two or three years in the air before landing. They will finally alight only to breed in a nest to which they will return every year after that.

• Dunlin may be summer visitors from Africa, winter visitors from Scandinavia or passage migrants from Iceland.

• Many Goldfinches move south in the autumn, mostly females. Female Chaffinches also leave Scandinavia in winter, some of which may arrive here. The deserted males gave rise to the scientific (if misleading) name for the Chaffinch: Fringilla coelebs (the bachelor finch).

• A few summer visitors, such as Blackcaps and Chiffchaffs, do not return to their winter regions, so are to be seen here in small numbers.

• Migration is sometimes linked to moulting. Seabirds and some wildfowl migrate to somewhere safe to moult because loss of flight feathers leaves them open to attack. Other birds moult before migrating.

• Crossbills are nomadic. They leave their breeding grounds to track their main food supply of spruce cones wherever they can find them.

• Waxwings, Bramblings and some tits, “erupt”. That is, large numbers leave an area when there is no longer enough food. Eruptions of Waxwings from Scandinavia happen every few years in late winter. Look for them on berry-bearing trees and bushes, often in supermarket carparks.

• Lots of birds do not migrate in family groups; males, females and young often move at different times and have different lengths of journey, some of them completely on their own. However wildfowl do migrate in families.

• As our climate changes, some species are migrating smaller distances or not at all. Fewer and fewer Bewick swans, for instance, are visiting the Somerset Levels in winter since they are now able to find enough winter food nearer to their Siberian breeding grounds.

Arctic Tern

Bullfinch