American bittern (Botaurus lentiginosus)

KingdomAnimalia
PhylumChordata
ClassAves
OrderCiconiiformes
FamilyArdeidae
GenusBotaurus (1)
SizeLength: 58.4 - 86.4 cm (2)
Wingspan: c. 107 cm (3)

The American bittern is classified as Least Concern (LC) on the IUCN Red List (1).

The American bittern (Botaurus lentiginosus) is a stocky wading bird best known for the male’s unique, loud, guttural call which has led to it being given a number of nicknames, including ‘thunder pumper’, ‘water belcher’ and ‘mire-drum’ (4) (5). This call, most frequently heard at dusk during the spring mating season, is produced from a specialised oesophagus (food pipe) and has a particularly powerful ‘booming’ quality (5). 

The American bittern is cryptically-coloured, which aids its ‘stand and wait’ hunting behaviour – like most bitterns this species is often observed standing motionless in tall emergent vegetation, with the bill held horizontal and the eyes focused downwards to spot prey (2). The adult is rich brown above, with varying amounts of black flecking and vertical, brown streaks, and white on the underparts. The crown is rusty-brown, and there is a black stripe extending down the neck. During the breeding season, two small patches may appear on the back, as well as inconspicuous white patches on the shoulders (2) (3). The bill is dull yellow with a dusky tip on the upper mandible, and the legs and feet are greenish-yellow (3). 

The male and female American bittern are similar in appearance, although the male is generally larger (2). The juvenile differs in lacking black throat patches (3).  

The American bittern is distributed widely across North and Central America. In the summer months it is found as far north as Alaska, U.S., and in Newfoundland and the Canadian Provinces, to central British Columbia, Canada. In the winter, the American bittern migrates as far south as Central America and the northern Caribbean islands (2).

The American bittern typically inhabits freshwater wetlands with tall, emergent vegetation. When breeding, it prefers ephemeral wetlands and marshlands (6), but will also forage along shorelines and in wet meadows, often showing a preference for areas with much open water and plant cover (2). 

During the winter, the American bittern occupies similar habitats to those during breeding, but a wider range of habitats is utilised, including managed wetlands, brackish coastal waters and dry grasslands (3).

American bitterns consume insects, crayfish, and small fish. Its primary foraging strategy is ‘stealth hunting’ whereby it remains motionless in a camouflaged area, and then strikes with the bill (6). 

Pair bonding begins in early April as the American bittern arrives at its breeding grounds. Male American bitterns reach the breeding grounds first and begin defending a territory. As the females arrive, males begin a courtship ritual that involves emitting a call described as a “dunk-a-doo” or a “pump-er-lunk” (6). The behaviour of the male American bittern during courtship has been described as a retching motion, where it repeatedly bends forward with the bill close to the ground (7). Egg-laying typically occurs in May and June. Multiple nests are frequently found in a single territory, which suggests that male American bitterns are polygamous (2). 

A single clutch of two to seven eggs is laid and incubated for about four weeks. The female American bittern feeds the nestlings through repeated regurgitation for one to two weeks, until the nestlings are able to leave the nest. The mother continues to feed the young after they leave the nest, but the role of the male is unknown (6).

The greatest threat to the American bittern is the loss of habitat due to agricultural conversion. Wetland loss has been occurring in the U.S. since European colonisation, and over half the original wetlands in mainland U.S. have already been destroyed. Inland, freshwater wetlands, which are the most important nesting and wintering habitats for the American bittern, are among the most threatened habitats in the U.S. (3) (4). 

Another concern associated with agricultural development is the contamination of water from chemicals and cattle waste, as well as eutrophication and siltation (3) (6). Human disturbance can also degrade habitat quality (4).

As a result of concern surrounding the decline of this species’ populations, the American bittern was listed by the U.S. Fish and Wildlife Service as a Nongame Species of Management Concern in 1987 and was included on the National Audubon Society’s Blue List in 1976 (2). It also receives protection under the Migratory Bird Treaty Act of 1918 (6). 

Although the American bittern has not been the target of any direct conservation measures, efforts have been made to preserve wetland habitat, for instance through the Wetland Reserve Program. Wetlands used by the American bittern should be protected to prevent further declines in its populations, while these habitats should also be free from chemical contamination, siltation, eutrophication, and other forms of pollution that harm the birds or their food supplies. Remarkably little is known about the American bittern’s biology so there is a need for further study of this species (4) (6).

Find out more about the American bittern:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
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  1. IUCN Red List (August, 2011)
    http://www.iucnredlist.org/
  2. EPA Species Profile - American bittern (August, 2011)
    http://www.epa.gov/region1/ge/thesite/restofriver/reports/final_era/B%20-%20Focus%20Species%20Profiles/EcoRiskProfile_american_bittern.pdf
  3. Montana Field Guide - American bittern (August, 2011)
    http://fieldguide.mt.gov/detail_ABNGA01020.aspx
  4. Lowther, P., Poole, A.F., Gibbs, J.P., Melvin, S. and Reid, F.A. (2009) American bittern (Botaurus lentiginosus). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
    http://bna.birds.cornell.edu/bna/species/018/
  5. State of Connecticut Department of Energy and Environmental Protection - American bittern (August, 2011)
    http://www.ct.gov/dep/cwp/view.asp?q=325954
  6. Wiggins, D.A. (2006) American Bittern (Botaurus lentiginosus): A Technical Conservation Assessment. USDA Forest Service, Rocky Mountain Region. Available at:
    http://www.fs.fed.us/r2/projects/scp/assessments/americanbittern.pdf
  7. Johnsgard, P.A. (1980) Copulatory behaviour of the American bitter. The Auk, 97: 868-869.