For Britain’s twitchers, those hard-core birders whose sole aim is to track down and see rare birds that have wandered to our shores, October is the highlight of the annual calendar. Towards the end of the autumn migration season, when most common birds have already departed and only the last few stragglers from farther north are passing through, a new group of birds begins to appear.
These birds are the vagrants, those rare and irregular species that make up more than half the birds on the official British List.
The reason we have so many rare birds is down to three factors: history, geography and weather. Historically, the British have always gone in search of rare birds, pioneering studies at far-flung locations, such as Fair Isle, over a century ago, so that rare visitors were identified and recorded. Geographically we are at a crossroads, on the edge of the vast Eurasian landmass, uniquely placed to attract avian wanderers from both east and west.
But most of all we have the weather: the prevailing westerly winds, combined with the jet stream, bring rare American songbirds from the other side of the Atlantic; and high-pressure systems over Siberia and Scandinavia bring birds from the east. Sometimes, if there is also a fast moving depression, migrants crossing the North Sea are forced to drift westwards and land on Britain’s east coast.
Among the more common species there is always the chance of a rarity who might have flown all the way from Siberia – essentially in the wrong direction – to end up in Yorkshire or Norfolk rather than Thailand.
