The Evolutionary Pull of Ocean Tides
In winter, the knots come by the thousands to feast on the riches in the intertidal mudflats of the Wash. These medium-size wading birds are rather dull and unprepossessing in appearance, white underneath and sandy on their backs. During the breeding season their plumage turns a rich russet, but this happens in the Canadian Arctic and other colder climes where the birds spend the summer, and we seldom see it. In Britain, knots are more remarkable for their sheer numbers.
Vast flocks of them put on a mesmerizing aerial performance over their feeding grounds: here in my county of Norfolk, in the Severn and Thames estuaries, in Morecambe Bay, and in other areas where sufficiently broad stretches of mud are exposed by the tide. The birds then pass the hour or two of high tide hidden in vegetation on slightly higher ground before returning to feed once more. At Snettisham in Norfolk, on the west-facing shore of the Wash, high-tide flights of 45,000 birds have been recorded.
The knots’ behavior is highly distinctive. Some wader species fly off at intervals as individuals when the tide comes and goes. Others, such as oystercatchers, turn their back on the water as the tide advances, and walk disconsolately, it seems, up the mud slope in time with the rising sea. But knots, perhaps because they cluster too tightly to move in this way, face the rising water and take off at the very last chance they have, when it has risen up their legs and threatens to wet their underfeathers.
I watch as they fly off in a continuous flourish like a magician’s curtain being swept aside. The dense flock swirls and feints like a single aerial organism. Once aloft, the birds first coalesce as an egg-shaped cloud low over the water, before gaining height and taking on ever more extravagant, twisted shapes like a pixelated flamenco dancer. As
