Voice - It is usually silent. In the breeding season, however, it makes a loud, resounding, guttural "pump-per-lunk" or "oonk-ka choonk" repeated up to five times as it gulps air and forces it over its bulging esophagus. It is most often heard in the evening. When flushed, it often makes a series of low "kok-kok-kok" calls or a single, loud "kwok" or "croak".
