It’s not hard to tell which people in a train station have just travelled across the world: they are the ones wearing hats because their hair is a mess. Long-distance migratory birds like the red knot Calidris canutus also have a tough job looking good - and appearance is important, because having reached their arctic breeding grounds, they need feathers preened to perfection to be attractive to potential mates. But, as if the non-stop 5000km flight wasn’t enough to guarantee the avian equivalent of a bad hair day