Thick-billed murres are the deepest diving birds in the world, capable of plummeting 200 metres below the surface of the water in less than a minute in search of fish. On land they are far less agile, but no less remarkable: they nest on narrow cliff ledges, as many as 20 pairs crammed into a single square metre, snuffling and preening, filling the air with guttural croaks and wheezes that sound like an old woman alternatively laughing and blowing her nose.