Nature Note

The wild weather of the past few days has delayed the seasonal migration of Bewick swans to their wintering grounds in Britain. Increasing cold in northern Europe, coming down from the Arctic, generally pushes them ever further south and west, as they move on in search of unfrozen grass (their staple food) and pondweed. In a normal year there would now be between 300 and 400 Bewicks at the Wildfowl and Wetlands Trust at Slimbridge, on the Severn, but in fact there are only 180-odd. This is partly the result of a poor breeding season: on the Arctic tundra, where the swans nest, the early summer was exceptionally cold, and only three cygnets have reached Slimbridge this year. Another diminishing influence has been the succession of south-westerly gales, which tend to keep the birds pinned down on the eastern side of England or on the Continent. In stormy weather they prefer to sit tight, provided they have enough food. There are now about 1,800 at Welney in Norfolk, and large numbers in the polders of Holland.

A cold spell, with northerly winds, will certainly push more over. Those that do reach British reserves live well on a diet of grass and supplementary grain, which builds up body weight for their marathon return journey to the Arctic in spring.