The Least bittern is amongst the smallest of the herons, adapted for living in dense marshes. Instead of wading in the shallows as most herons do, the Least bittern climbs about among reeds and cattails, clinging with its long toes to the stems. Its narrow body enables it to slip with ease through dense, tangled vegetation. Due to its choice of habitat, it is often unnoticed, except when it flies. However, its cooing and clucking sounds are often heard at dawn and dusk and also sometimes at night.
Least bitterns breed in areas from northern Argentina to southern Canada. They winter in California, Texas and Florida, down to Panama and Colombia. These birds live in large marshes that feature dense vegetation, freshwater marshes, pools and lakes with dense vegetation on the edges, and in brackish marshes and mangroves.
Least bitterns are diurnal, solitary and shy birds, living hidden in the thick vegetation of a marsh. On the approach of an intruder, a least bittern will run away instead of flying off, moving low over the tops of emergent vegetation. It will fly short distances before it drops back into the vegetation. When walking or running, it uses the stalks of plants as stepping-stones. With legs spread, it clutches one or several stalks in each foot, and steps forward. If threatened or alarmed, it may freeze on the spot with its bill pointed upright. Its brownish plumage and such a posture enable it to be very well camouflaged, and it may also sway from side to side, like reeds in the wind. These birds feed in small pools among the emergent vegetation, slowly walking at the edge of the water. It will stand and wait, with its legs spread apart, its head and neck stretched out low over the pool, its bill nearly touching the water. Once it has made a capture, the bird retreats back into the vegetation, then moves to another pool.
Least bitterns are carnivores (piscivores), they eat small fish, aquatic invertebrates, reptiles, amphibians and insects. They may also feed on the chicks and eggs of other marsh species.
Least bitterns are monogamous breeders, which means that one male mates with only one female. During courtship displays, the male and the female utter sounds, one in response to the other. Breeding varies seasonally, depending on location. In New York, least bitterns initiate breeding in late May to early June and by mid-May in Canada. This species sometimes nests in loose colonies. The nest is a fragile platform above the water, constructed on the bent over dead stalks of the emergent vegetation. The nest is mainly built by the male from fresh and dead plant stems, and a canopy made from tall marsh plants that are pulled over the platform. 2 to 5 eggs are laid, bluish-white and sparsely flecked with brown. 19 to 20 days is the period of incubation, shared by both parents. The young are fed by both parents and they fledge around 25 days after they have hatched. Least bitterns can produce two broods each season.
The major threats to Least bitterns consist of habitat loss as a result of the drainage of wet areas. Threats during the nesting period are human disturbances, including recreational water boats causing high waves that may destroy a nest and its chicks.
This bird has an extremely large range. According to the What Bird resource, the total number of the Least bittern population is around 130,000 individuals. According to the Species at Risk Public Registry resource, the total population size of the Least bittern in Canada is around 1,500 pairs. Overall, currently this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today remain stable.