Many a birdwatcher, while struggling in midwinter to separate the waders by sight, would have a very different experience as spring and summer approach, because suddenly these birds are utterly transformed. The Knot, in particularly, blushes into a startling brick-red, the sort that only a daft ‘celebrity makeover luvvie’ would use to paint an interior. Meanwhile the Dunlin goes for rich chestnut offset by a bold black belly; the effect ought to be impressive, but, in a way, it just looks as though it has mistakenly taken a bath in ink. Overall though, it is almost as though these birds are over-compensating in spring to be different from their winter selves, so very distinct do these relatives look. To go with their startling makeover is the voice. Knots, you may have noticed, are remarkably quiet birds in winter, especially in comparison to Redshanks and Oystercatchers, which are the loudmouths of the estuary. The best they can muster is an under-thebreath murmur. In the breeding areas, however, freed from the cramped conditions of their famous flocks, Knots relish fighting for their territory on the tundra, and lift into the cold Arctic air in song-flight uttering a clear, repeated ‘coo-ee’ with variations, sounding a little like an electronic alarm – perhaps a car alarm – going off. The Dunlin, meanwhile, has a rushed and hurried flight-song, which accelerates into a blast like a referee’s whistle, a longer version of their familiar buzzing call on an estuary. And while Knots invariably cast their territories over the more extreme Arctic tundra, up as far as 81°N in Greenland, Dunlin breed in all kinds of climatic conditions, even on boggy moorland in the UK. The difference is stark: while a Knot could in theory spot a polar bear while incubating, British Dunlin will have more benign company such as sheep and cows. Knots are essentially birds of dry tundra, while Dunlin usually go for much wetter areas. And the Knot exhibits an unusual nesting quirk, preferring to nest in clumps of a plant called Dryas (one of which is the Mountain Avens).