What is "bitterns"

Usage examples of "bitterns".

They could hear and occasionally see the swamp birds, the herons, the huge blue herons and the green ones, the bitterns, the white ibis with coral-colored legs and beaks, the grebes and the snake birds.

Now in a steep slant bitterns, sea swallows, and teals rise from the rushes and duckweed.

There were many other rooms, all filled with lords and ladies, all with entertainers: three different gleemen in their cloaks, more jugglers and tumblers, and musicians playing flutes, bitterns, dulcimers, and lutes, plus five different sizes of fiddle, six kinds of horn, straight or curved or curled, and ten sizes of drum from tambour to kettle.