The American bittern is a carnivorous wading bird that is best known for the unique, loud, guttural call made by the male, which has resulted in it being given several nicknames, including ‘water belcher’, ‘thunder pumper’, and ‘mire-drum’. This call, most often heard during the mating season in spring at dusk, is produced from the bird's specialized esophagus or food pipe, creating an especially powerful ‘booming’ quality. This stocky bird seems to materialize among reeds and to disappear as quickly, particularly when in its concealment pose, where it stretches its neck and points its bill skyward. These stealthy birds stand motionless amongst tall marsh vegetation, or will patiently stalk fish, frogs, or insects.
The American bittern occurs widely across Central and North America. In the summer it is found in the north as far as Alaska, and Newfoundland and central British Columbia in Canada. In winter, these birds migrate south to Central America and the northernmost Caribbean islands. They typically inhabit freshwater wetlands that have tall, emergent vegetation. During breeding, they prefer marshlands and ephemeral wetlands, but also forage in wet meadows and along shorelines, often preferring areas with much plant cover and open water.
An American bittern is a solitary forager, standing motionless or slowly walking with outspread toes as it searches for food. It hunts during the day, especially at dawn or dusk. Possibly its most famous behavior is its stance when it feels threatened. It points its bill to the sky, stretches out its body, and will even sway with the breeze, in order to blend in with the reedy surroundings. So ingrained is this pose that it will sometimes use it even when out in the open. These birds do not socialize much except when migrating in small groups, or during mating, or facing off over territories - and this can be dramatic. Males in competition with each other will crouch down and approach one another, displaying the white plumes that are between their shoulders. These moves can escalate into a chase in the air, the combatants spiraling upwards, while trying to stab their opponent with their bill.
America bitterns are polygynous breeders. Male and female do not really interact with each other except for copulation, though a female may site her nest close to a "booming" male in order to distract predators from her hatchlings. Pair formation takes place in early May when females arrive at the nesting area. The female chooses her nest site, usually amongst dense emergent vegetation above water of a depth of 4-5 cm. The female constructs the nest out of reeds, cattail, sedges, or other emergent vegetation. The female lays 2-7 eggs in one clutch, with incubation beginning before all the eggs are laid and lasting 24 to 28 days. Only the female carries out brooding and feeding duties. The hatchlings leave their nest in one to two weeks, but receive supplemental feeding for up to another four weeks after hatching.
This bird has an extremely large range. The population of American bitterns is undergoing a major decline due to degradation and loss of habitat. Eutrophication (where an ecosystem is enriched with chemical nutrients), chemical contamination, siltation, and human disturbance have greatly reduced habitat quality due to damage to the food supply. Habitat quality has also been eroded by stabilized water regimes and changes in wetland isolation. Acid rain also damages the wetlands.
According to the What Bird resource, the total population size of the American bittern is around 3 million individuals. Currently this species is classified as Least Concern (LC) on the IUCN Red List, but its numbers today are decreasing.