Cold weather halts migration!
A return to north-easterly winds has brought much colder air from Scandanavia and Eastern Europe causing the Bewick’s swans to delay their migration back to Russia for considerably longer than usual. This morning, 179 swans were recorded at Slimbridge, the highest number seen here at this time of year for 20 years! Like many long distant migrants breeding at high latitudes, the timing of migration is crucial as there is only a short window of opportunity to breed over the summer before the onset of the arctic winter. Day length is a reliable indicator of season for the Bewick’s and is therefore thought to be the key trigger for migration. The swans at Slimbridge have certainly become more restless as the days have lengthened in recent weeks, with many undertaking frequent short practice flights around the area. Although day length frames the broad migratory period, weather conditions influence the precise timings of departure. Past WWT research has found wind direction to be important and the north-easterly winds we are encountering at the moment are almost certainly causing their migration to grind to a halt – it would be very hard work flying into such a strong headwind!
The fact that there are so many Bewick’s swans left today is even more remarkable given that there were more swans wintering at Slimbridge 20 years ago than there are now. Sadly, it is not just Slimbridge that has received fewer arctic visiting swans in recent years – the number of Bewick’s wintering across the whole of Northwest Europe has reduced from 29,000 birds to less than 20,000 since the mid-1990s. WWT are working with ornithologists across Europe to determine the main causes of the decline.
Among those still making the most of Slimbridge hospitality are Slimbridge faithfuls Rosso and Bianco who have been visiting the reserve for 13 years!
