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American Bittern - Botaurus lentiginosus
Species of Concern Native Species Global Rank :
G5
State Rank :
S3B
(see State Rank Reason below)
Agency Status USFWS :
MBTA
USFS :
BLM :
SENSITIVE
FWP SWAP :
SGCN3
PIF :
3
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Copyright by Borror Laboratory of Bioacoustics, Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, OH, all rights reserved.
State Rank Reason (see State Rank above)
The American Bittern is dependent on large wetland complexes, which have declined across the species range. Declines in Montana and the species specialized habitat requirements warrant general concern about the persistence of the species.
Details on Status Ranking and Review
American Bittern (Botaurus lentiginosus ) Conservation Status Review
Population Size
Score U - Unknown
Comment Unknown.
Range Extent
Score G - 200,000-2,500,000 km squared (about 80,000-1,000,000 square miles)
Comment 380530 square kilometers based on Natural Heritage Program range maps
Area of Occupancy
Score F - 500-2,000 km squared (about 125,000-500,000 acres)
Comment 1,192 square kilometers based on GAP predicted model.
Long-term Trend
Score D - Moderate Decline (decline of 25-50%)
Comment High wetland habitat loss since the time of European arrival. Species is dependent on wetlands.
Short-term Trend
Score U - Unknown. Short-term trend in population, range, area occupied, and number and condition of occurrences unknown.
Comment Breeding Bird Survey (BBS) is very limited, but 1966-2007 trend is -10.4% per year; BBS 1980-2007 trend is -9.8% per year
Threats
Score F - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant portion of the population or area.
Comment Wetland alteration and loss caused by drought and lack of water resources. Pesticides, herbicides, and other contaminants.
Severity Low - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.
Comment Require water in wetland, when water is lost animals will recolonize quickly if water is returned.
Scope High - > 60% of total population or area affected
Comment Climate continues to dry and water resources are already stressed across their range in Montana.
Immediacy Moderate - Threat is likely to be operational within 2-5 years.
Comment Ongoing drought years, but climate change expected to dry even further.
Intrinsic Vulnerability
Score B - Moderately Vulnerable. Species exhibits moderate age of maturity, frequency of reproduction, and/or fecundity such that populations generally tend to recover from decreases in abundance over a period of several years (on the order of 5-20 years or 2-5 generations); or species has moderate dispersal capability such that extirpated populations generally become reestablished through natural recolonization (unaided by humans).
Environmental Specificity
Score A - Very Narrow. Specialist. Specific habitat(s), substrate(s), food type(s), hosts, breeding/nonbreeding microhabitats, or other abiotic and/or biotic factor(s) are used or required by the Element in the area of interest, with these habitat(s) and/or other requirements furthermore being scarce within the generalized range of the species within the area of interest, and, the population (or the number of breeding attempts) expected to decline significantly if any of these key requirements become unavailable.
Comment Large wetlands with emergent vegetation species is dependent on are not that common in Montana.
General Description
A stocky wading bird with a straight pointed bill, relatively short neck and legs, and somewhat pointed wings; darker flight feathers; bill dull yellow with a dusky tip on the upper mandible; legs and feet are greenish yellow; breeding feathering includes generally inconspicuous white ruffs on the shoulders and two small green patches on the back; wing span 107 cm. The American Bittern is a brown, medium-sized heron, 60-85 cm long, with a stout body and neck and relatively short legs (Palmer 1962, Cramp 1977, Hancock and Kushlan 1984). Adult plumage is all brown above and finely flecked with black; heavily streaked with brown and white below. The crown is rusty-brown. An elongated, black patch extends from below the eye down the side of the neck, a characteristic unique among herons (Hancock and Kushlan 1984). The throat is white. Sexes are similar, except that the male is slightly larger (Gibbs et al. 1992). Juveniles differ only in lacking black neck patches, which are obtained in the first winter. Plumage does not change seasonally.
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see
Marks et al. 2016, Birds of Montana. Diagnostic Characteristics
Differs from night-herons in the following ways: wings are pointed rather than rounded; flight feathers are much darker than back (vs. no contrast), upperparts lack white spotting; and bill is more slender. Much larger than the Least Bittern (average length 71 cm vs. 33 cm). Differs from similar juvenile Green Heron in being larger (length 71 cm vs. 46 cm) and in having flight feathers of wings obviously darker than the middle of the back.
Species Range
Montana Range
Range Descriptions Western Hemisphere Range
Range Comments
American Bitterns breed across a large portion of Canada and the U.S., occurring from n. British Columbia and s. Northwest Territories to Newfoundland in the north and from s. California to Virginia in the south. They winter inland across the southern tier of the U.S. south through Mexico to Guatemala and Belize, along both coasts from British Columbia and New Jersey to Nicaragua, and in parts of the West Indies.
Observations in Montana Natural Heritage Program Database
Number of Observations: 722
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
Relative Density
Recency
SUMMER (Feb 16 - Dec 14)
Direct Evidence of Breeding
Indirect Evidence of Breeding
No Evidence of Breeding
WINTER (Dec 15 - Feb 15)
Regularly Observed
Not Regularly Observed
(Observations spanning multiple months or years are excluded from time charts)
Migration
Bitterns typically arrive from late April to early May, nest from late May through July, and are gone by late September. The earliest sighting was at Terry on 23 April 1893 (Cooke 1913) and the latest was on the Missoula CBC on 19 December 1981; the latter record is the only documented occurrence on a Montana CBC.
Habitat
American Bitterns favor large freshwater wetlands with tall emergent vegetation such as cattails and bulrushes. Sparsely vegetated wetlands are occupied occasionally, tidal marshes rarely. The typical nest is a platform of dried rushes, sedges, and cattails placed in dense emergent vegetation over shallow water (Gibbs et al. 1992). Bitterns forage along shorelines, in dense marsh vegetation, and in wet meadows. Winter range include areas where temperatures stay above freezing and waters remain open. Managed wetlands, such as those at wildlife refuges, are often used.
Ecological Systems Associated with this Species
Details on Creation and Suggested Uses and Limitations
How Associations Were Made
We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for
vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.
In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.
However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system,
even if point observations were associated with that system.
Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.
The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.
If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.
Suggested Uses and Limitations
Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.
These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at:
mtnhp.org/requests ) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.
Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.
Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.
Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).
Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.
Literature Cited
Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
Dobkin, D. S. 1992. Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34. Missoula, MT.
Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998. Montana atlas of terrestrial vertebrates. Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT. 1302 p.
Hutto, R.L. and J.S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32. 72 p.
Maxell, B.A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to U.S. Forest Service Region 1. Missoula, MT: Wildlife Biology Program, University of Montana. 161 p.
Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath. 2004. Amphibians and reptiles of Montana. Missoula, MT: Mountain Press Publishing Company. 262 p.
Food Habits
American Bitterns eat mainly insects, amphibians, crayfish, small fish and small mammals, occasionally garter snakes at pond margins. Contents of 133 stomachs with food items comprised 23% insects, 21% amphibians, 21% fish, 19% crayfish, 10% small mammals, 5% snakes, and smaller quantities of crabs, spiders and other invertebrates (Gibbs et al. 1992). One collected in the Flathead Lake region was filled with dragonflies (Silloway 1903)
Ecology
During the breeding season, males repeat from two to ten times a distinctive, far-carrying call, rendered as "pump-er-lunk " (Gibbs et al. 1992), and which is often preceded by a series of clicking and gulping sounds. Relies on stealth more than pursuit to forage. Waits motionless for long periods to capture passing prey. In flight, bitterns seem hurried, ungraceful, and stiff. When disturbed, they often freeze in an upright, concealing posture, with head and bill upturned. The BBS is a poor means of surveying bitterns, and little is known about population trends and general biology throughout their range. Viewed as decreasing in numbers in the Fortine area (Weydemeyer 1975).
Reproductive Characteristics
Nests with eggs have been found in Montana as early as 1 June, and flightless young have been seen into late July and early August (Montana Bird Distribution Committee 2012). A nest with one fresh egg was found 19 June at Bowdoin NWR (Willett 1907). In the Fortine area, data from 10 nests in hayfields included a nest with 5 eggs on 4 June, newly hatched young 8 July, and records for third-grown young range from 22 July to 1 August (Weydemeyer 1975). Clutch size across the range is 2 to 7 eggs (Gibbs et al. 1992).
Management
No management activities specific to American Bittern are currently occuring in Montana. A clear need exists to monitor numbers and assess nesting success and productivity in the state. Protection of large wetlands (> 10 ha) with emergenct vegetation is the most urgent management need.
Threats or Limiting Factors
Owing to 200 years of wetland losses in the U.S., numbers almost surely have declined since European colonization. Eutrophication, siltation, chemical contamination, and human disturbance also seriously degrade habitat quality. Isolation of wetlands and stabilized water regimes may also contribute to reduced habitat quality.
References
Literature Cited AboveLegend:
Additional ReferencesLegend: Do you know of a citation we're missing? Botaurus lentiginosus ). Species Account Number 018. The Birds of North America Online (A. Poole, Ed.). Ithaca, NY: Cornell Laboratory of Ornithology; Retrieved 3/25/2008 from The Birds of North America Online databaseEffects of recreation on Rocky Mountain wildlife: a review for Montana . [Montana]: Montana Chapter of the Wildlife Society.
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