Bittern

The boom

The bittern’s boom is one of the most evocative sounds in British wildlife. Males produce this extraordinary foghorn call — a deep, resonating ‘oomph’ repeated slowly several times — primarily from dusk to dawn in spring. The sound is produced by inflating the oesophagus and is amplified by the reed beds that surround the bird. Historically common across British marshes, the boom was heard widely; as fens were drained, it became vanishingly rare.

Cryptic camouflage

The bittern’s streaked brown plumage is perfectly matched to dry reed stems. When alarmed, it adopts a freeze posture — stretching its neck vertically, pointing its bill skyward, and swaying gently with the reeds. In this pose, even a large bird (up to 80 cm tall) becomes almost completely invisible. Bitterns will hold this pose for many minutes, even as observers stand a few metres away.

Reed bed recovery

Bitterns nearly went extinct as a British breeding bird in the early 20th century as reed beds were drained for agriculture. A dedicated conservation programme from the 1990s — creating and managing extensive reedbeds at nature reserves — brought the British population from just 11 booming males in 1997 to over 200 by 2020. The recovery is one of British conservation’s greatest success stories.

Fishing strategy

Bitterns are patient, ambush hunters of fish, frogs, eels, and invertebrates. They stand motionless at the reed edge, then strike with explosive speed. Their eyes face partly downward, giving them a clear view of the water below their bill even when their head is raised.