The commonest call is a quick, rasping "tsjätsch" given just as the bird takes off when disturbed. During the display flight at dusk and in darkness the male produces one of the strangest sounds in the bird world: a mechanical humming "bleating" that does not come from the throat at all but from the outermost tail feathers, which are spread out and set vibrating as the male dives steeply towards the ground at high speed. The sound carries far across the open mire landscape and has given the species the folk name "sky goat". The display flight is most often performed at dusk and in the early evening during May–June and is the surest way to locate breeding birds.