Catching crayfish is their specialty. They nest singly and in small colonies, sometimes with other herons. The stick nest is built in a tree or shrub and sometimes lined with fine twigs, rootlets or leaves. Both sexes build, or they may re-use an old nest. This species is more secretive in its nesting habits than other herons, with the exception of bitterns.
Incubation is by both sexes.
This shy bird is not often observed, partly because it usually hides in tall grasses and sedges at the hint of trouble, but mostly because the bird is predominantly nocturnal. Their call is three or four low, soft coos. Least bitterns regularly breed in emergent and brushy wetlands in the glaciated wetlands of northwestern counties and at Presque Isle. The species nests elsewhere, but irregularly, wherever suitable habitat exists. The species nests on the ground in marshes, bogs or brackish water areas.