Botaurus lentiginosus

Although not particularly small (around 23 inches), the American Bittern’s mottled brown plumage and short, thick build provide it with excellent camouflage in its heavily vegetated habitat. This heron may be best identified by its coloration, short yellow legs, white throat, and black neck stripes. Male and female American Bitterns are similar to one another in all seasons. The American Bittern breeds widely across the northern United States and the southern half of Canada. In winter, American Bitterns migrate to coastal areas of the United States south to Mexico, Central America, and the West Indies. This species may be found all year along the Pacific coast as well as in the Mid-Atlantic Region. American Bitterns breed primarily in shallow, heavily-vegetated freshwater wetlands. In winter, this species utilizes many of the same habitat types as in summer, but some bitterns wintering close to the coast may be found in brackish water. American Bitterns primarily eat animal matter, both invertebrates (mainly insects) and vertebrates (including fish, amphibians, and small mammals). Due to its short stature and the nature of its habitat, American Bitterns are difficult to observe while feeding or standing still. Bitterns may be more visible in the air, undertaking short flights above the top of the marsh grass. This species is primarily active during the day.

Threat Status: Least concern

During the breeding season, the American Bittern ranges from the Mid-United States to northern Canada. Its wintering range stretches from the south Atlantic coast across the Gulf coast and west to southern California.

Biogeographic Regions: nearctic (Native )

Alaska to Mexico; winters to Panama and West Indies.

During the breeding season, the American Bittern ranges from the Mid-United States to northern Canada. Its wintering range stretches from the south Atlantic coast across the Gulf coast and west to southern California.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: southeastern Alaska and southern Mackenzie to Newfoundland, south to southern California, central Arizona (formerly), southern New Mexico, central Kansas, central Missouri, central and western Tennessee, western Kentucky, central Ohio, southern Pennsylvania, northeastern West Virginia, eastern Maryland, and eastern Virginia (rarely North Carolina); locally in Texas, Louisiana, Florida, and Mexico south to Puebla and the state of Mexico (AOU 1983). In the northeastern U.S., abundance declines sharply south of northern New England and New York (Gibbs and Melvin 1992). Range is large but highly discontinuous due to restricted habitat. NON-BREEDING: southwestern British Columbia, northern Nevada, northern Texas, Ohio Valley (rarely), and New York south to southern Mexico (rarely or formerly to Panama) and the West Indies (AOU 1983). Occurs in winter primarily near the coast; areas of relatively high density include southern Florida, San Joaquin Valley (California), eastern North Carolina (no longer common, H. LeGrand, pers. comm.), Okefenokee Swamp, southern Louisiana, and various national wildlife refuges elsewhere (Root 1988).

The American Bittern is a medium-sized heron with a stout body and a neck, short legs, and a white neck. The upperside of the bird is brown finely speckled with black. The undersides are heavily streaked with brown and white. There is a long black patch that extends from below the eye down the side of the neck.

Average mass: 600 g.

Average basal metabolic rate: 2.7412 W.

The American Bittern is a medium-sized heron with a stout body and a neck, short legs, and a white neck. The upperside of the bird is brown finely speckled with black. The undersides are heavily streaked with brown and white. There is a long black patch that extends from below the eye down the side of the neck.

Average mass: 600 g.

Average basal metabolic rate: 2.7412 W.

Length: 71 cm

Weight: 706 grams

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.

In the breeding range, the American Bittern inhabits areas of freshwater wetlands with tall emergent vegetation, shorelines, and vegetative fringes. The bird prefers beaver-created wetlands to those of glacial origin.

Terrestrial Biomes: forest ; rainforest

Systems

• Terrestrial
• Freshwater

In the breeding range, the American Bittern inhabits areas of freshwater wetlands with tall emergent vegetation, shorelines, and vegetative fringes. The bird prefers beaver-created wetlands to those of glacial origin.

Terrestrial Biomes: forest ; rainforest

Comments: BREEDING: Primarily large freshwater and (less often) brackish marshes, including lake and pond edges where cattails, sedges, or bulrushes are plentiful and marshes where there are patches of open water and aquatic-bed vegetation. Occurs also in other areas with dense herbaceous cover, such as shrubby marshes, bogs, wet meadows, and, rarely, hayfields (Brewer et al. 1991). Readily uses wetlands created by impoundments. Wetlands of 2.5 ha or more may support nesting; smaller wetlands may serve as alternate foraging sites (Gibbs and Melvin 1992). See Hanowski and Niemi (1990) for a quantitative study of habitat in Minnesota.

Nests primarily in inland freshwater wetlands, sometimes in tidal marshes or in sparsely vegetated wetlands or dry grassy uplands. Breeding occurs primarily in wetlands with tall emergent vegetation. Sparsely vegetated wetlands and dry grassy uplands are sometimes used, as are tidal marshes in some areas (Stewart and Robbins 1958, Swift 1987). In comparison to the sympatric least bittern (IXOBRYCHUS EXILIS), uses a wider variety of wetland cover types, less densely vegetated sites, shallower water depths, and primarily freshwater habitats.

Wetlands used in Maine were dominated by emergent and aquatic-bed (floating-leaved and submergent) vegetation, had a high diversity of vegetative life forms, and a high degree of cover/water interspersion (Gibbs et al. in press; Gibbs and Melvin 1990). Portions of wetlands used were dominated by sedges (CAREX spp.), broad-leaved cattail (TYPHA LATIFOLIA), and ericaceous shrubs. In a study of Quebec lakes, lakes with patches of floating-leaved plants, emergent growth along shorelines, and abundant amphibian populations were preferred (DesGranges and Houde 1989).

At Horicon Marsh in Wisconsin, responded to tape-recorded calls only from shallow water cattail and dry cattail habitats and seemed to avoid deepwater cattails (Manci and Rusch 1988). At moist soil impoundments in Missouri, associated with water depths of less than 10 cm and vegetative cover characterized as "rank, dense, or sparse." Habitat use was not associated with "open" or "short" vegetative cover or water of depths of greater than 10 cm (Fredrickson and Reid 1986). In Minnesota, seven breeding territories had a mean water depth of 10 cm, vegetation height of 1.3 m, and density of sedge and grass stems of 117 stems/m squared (Hanowski and Niemi 1986).

NON-BREEDING: Migrant bitterns were flushed at 25 sites during spring in Missouri with mean water depth of 26 cm, vegetation height of 63 cm, and stem density of 157 stems/m squared. Characteristics of 35 flush sites in fall were similar, except that vegetation was taller (118 cm) (Reid 1989). In areas where temperatures stay above freezing and waters remain open, especially in coastal regions where the ocean moderates climate (Root 1988). Wintering habitat is much like breeding habitat, and overwintering populations are heavily dependent on managed wetland areas, such as those occurring at wildlife refuges (Root 1988). Occasionally occurs in habitats that are more open than the usual ones. Overwintering occasionally takes place in brackish coastal marshes (Hancock and Kushlan 1984).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

These birds arrive at nesting areas in the northeastern U.S. in mid to late March, about a month before the more southerly wintering least bittern (Bent 1926), but peak numbers of birds may not arrive until mid-April (Palmer 1962). Arrives in the Great Lakes region primarily in April. Wanders considerably after breeding. Southward migration extends from September to October and November (Palmer 1962).

The basic diet of the American Bittern includes insects, amphibians, crayfish, and small fish and mammals. When foraging, it relies mostly on stealth, waiting motionless for its prey to pass by. Its coloration adds to its ability to go undetected by prey. When its prey is in reach, the bird darts forward and seizes the prey in its bill. The prey is then killed by biting or shaking and is swallowed head first. Microhabitats for foraging include vegetation fringes and shorelines. Even-aged stands of older, dense or dry vegetation are avoided.

The basic diet of the American Bittern includes insects, amphibians, crayfish, and small fish and mammals. When foraging, it relies mostly on stealth, waiting motionless for its prey to pass by. Its coloration adds to its ability to go undetected by prey. When its prey is in reach, the bird darts forward and seizes the prey in its bill. The prey is then killed by biting or shaking and is swallowed head first. Microhabitats for foraging include vegetation fringes and shorelines. Even-aged stands of older, dense or dry vegetation are avoided.

Comments: Eats mainly fishes, crayfishes, amphibians, mice and shrews, insects, and other animals (Palmer 1962). Feeds young by regurgitation. Stealthy forager. The trunk is highly compressed to facilitate movement through dense vegetation. The repertoire of feeding behaviors is relatively small. Of 28 recognized heron foraging behaviors (Kushlan 1978), only four are used: standing in place, neck swaying (which may enable bitterns to overcome glare or permit a quicker strike by having muscles in movement when strike begins), walking slowly, and walking quickly. This is a solitary feeder that relies more on stealth than pursuit to capture prey. Its coloration, particularly its ventral stripes, provides camouflage in dense, vertical marsh vegetation, complements its inactive feeding repertoire, and permits solitary foraging (Kushlan 1978). Crypsis is thought to function mostly to reduce visibility to prey and competitors rather than to predators (Kushlan 1978).

The long, thick bill enables the taking of a variety of large and small prey (Kushlan 1978), a conclusion supported by analyses of stomach contents. Based on 160 specimens (133 with food remains) collected throughout North America, stomach contents included insects (23%, including many Odonates), frogs and salamanders (21%), fish (21%, including catfish, sunfish, yellow perch, suckers, killifishes, and sticklebacks), crayfish (19%), mice and shrews (10%), snakes (5%), and small quantities of crabs, spiders, and unidentified invertebrates (Cottam and Uhler 1945). Nine stomachs from Pennsylvania contained fish, frogs, crayfish, watersnakes, snails, beetles, and grasshoppers (Warren 1890). Have been observed intercepting dragonflies in midair (Dudones 1983). Garter snakes (THAMNOPHIS SIRTALIS) feeding on frogs at pond margins are occasionally eaten (Ingram 1941). A captive individual ate 23.9 g (dry weight) of food (mice) per day, and required 22 hours to digest a meal and eject a pellet (Rhoades and Duke 1975).

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

10,000 - 1,000,000 individuals

Comments: Difficult to estimate due to its secretive nature.

Basically solitary. Low population density. Too little is known of rates of predation on nests and adults to infer the importance of predation as a factor limiting populations. Similarly, only minimal information is available on the effects of parasites and disease. Wading birds are known to be susceptible Type C botulism (occasionally), avian cholera (infrequently), chlamydial infections (frequently), sarcocystis (rarely), and aspergillosis (infrequently) (Friend 1987). Known to harbor lice and flies (Peters 1936) and a number of species of nematodes (Boyd 1966).

Comments: More active when light intensity is low (Palmer 1962).

Range lifespan
Status: wild: 8.3 (high) years.

Average lifespan
Status: wild: 100 months.

Range lifespan
Status: wild: 8.3 (high) years.

Average lifespan
Status: wild: 100 months.

Maximum longevity: 8.3 years (wild)

The American Bittern is considered monogamous; however, it is possibly polygynous under some circumstances. Pair formation occurs in early May when the female arrives at the nesting site. The female then chooses the nest site, which is usually in dense emergent vegetation over water that is 4-5 cm in depth. The nest is built by the female and is constructed of reeds, sedges, cattail, or other emergent vegetation. Egg laying is performed daily with one egg laid in the in the morning. Incubation begins before the full clutch is laid and lasts 24 to 28 days. Brooding and feeding duties are performed solely by the female. The hatchlings leave the nest after one to two weeks, but they receive supplemental feedings by the adults up to four weeks after hatching.

Average time to hatching: 34 days.

Average eggs per season: 4.

The American Bittern is considered monogamous; however, it is possibly polygynous under some circumstances. Pair formation occurs in early May when the female arrives at the nesting site. The female then chooses the nest site, which is usually in dense emergent vegetation over water that is 4-5 cm in depth. The nest is built by the female and is constructed of reeds, sedges, cattail, or other emergent vegetation. Egg laying is performed daily with one egg laid in the in the morning. Incubation begins before the full clutch is laid and lasts 24 to 28 days. Brooding and feeding duties are performed solely by the female. The hatchlings leave the nest after one to two weeks, but they receive supplemental feedings by the adults up to four weeks after hatching.

Average time to hatching: 34 days.

Average eggs per season: 4.

Nesting occurs solitarily (non-colonially) on all-purpose territories that provide both feeding and nesting sites, but occasionally up to a few pairs nest in a small area (Harrison 1979). Polygyny is suspected to occur (Palmer 1962). Mating rituals are elaborate, and involve display of a tuft of white nuptial feathers located on the sides of the neck (see Baker 1980, Johnsgard 1980). BOTAURUS bitterns may undergo a change in iris color from yellow to orange during courtship (Wood 1986).

The nest consists of a platform of reeds, sedges, cattail, or other available emergent vegetation, and is lined with fine grasses. Nests are usually placed on the ground, in a tussock, a few inches above water, or are floating; are surrounded by water, and have dense, overhead cover (Bent 1926, Vesall 1940, Cogswell 1977, Harrison 1978, Terres 1980). Nests may also be built in grassy uplands (Vesall 1940, Duebbert and Lokemoen 1977). Nests are usually accessed by two, well-beaten pathways (Gabrielson 1914).

Egg-laying begins in late April or early May, about a month after the arrival at nesting areas, and continues until mid-June (Bent 1926). In the north-central U.S., nests may contain eggs from about early May to early July (Brewer et al. 1991). Clutch size ranges from two to seven eggs, usually three to five (Duebbert and Lokemoen 1977, Graber et al. 1978). Incubation, by the female only, begins with the first egg (Palmer 1962). Hatching occurs after 24-28 days (Burns 1915, Bent 1926, Vesall 1940), and chicks remain at or near the nest for two weeks (Gabrielson 1914, Vesall 1940, Harrison 1979, Terres 1980). Chicks are fed only by the female, and are given fish, frogs, snakes, crayfish, and mice (Gabrielson 1914, Byers 1951). Nests often become fouled with food debris (Vesall 1940). Post-fledging behavior of young is unreported.

Apparently single-brooded (Palmer 1962). In upland habitats in North and South Dakota, 57% of 72 nests hatched at least one egg (Duebbert and Lokemoen 1977). Little is known about sources of egg, chick or post-juvenile mortality, age at fledging or first breeding, or territory size. Age at fledging for the closely-related Eurasian bittern is 50-55 days (Cramp 1977). One banded American bittern lived at least eight years (Clapp et al. 1982). Probably undergoes extensive post-breeding dispersal, which has resulted in numerous sightings, mostly between September and December, at locations as distant as Iceland, Norway, and Great Britain (Cramp 1977). Information on molt is incomplete. Adults undergo a complete post-breeding molt from August to November, and possibly a pre-breeding renewal of body plumage (Palmer 1962, but see Bent 1926).

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 3 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

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Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Specimens with Barcodes: 4
Species With Barcodes: 1

Canada

Rounded National Status Rank: N5B,N3N : N5B: Secure - Breeding, N3N: Vulnerable - Nonbreeding

United States

Rounded National Status Rank: N4B,N4N : N4B: Apparently Secure - Breeding, N4N: Apparently Secure - Nonbreeding

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Widespread distribution but populations are declining; threat of habitat destruction.

The American Bittern population is undergoing a substantial decline due to loss and degredation of habitat. The species was listed as a Nongame Species of Management Concern by the United States Fish and Wildlife Service in 1982 and 1987. It is listed as a species of special concern in the state of Michigan. Eutrophication, siltation, chemical contamination, and human disturbance have significantly reduced habitat quality by damaging the food supply. Changes in wetland isolation and stabilized water regimes are also eroding habitat quality. Acid rain is also another significant threat to the species due to its damaging effects on wetlands.

IUCN Red List of Threatened Species: least concern

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: special concern

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 2008
  Least Concern
• 2004
  Least Concern

The American Bittern population is undergoing a substantial decline due to loss and degredation of habitat. The species was listed as a Nongame Species of Management Concern by the United States Fish and Wildlife Service in 1982 and 1987. It is listed as a species of special concern in the state of Michigan. Eutrophication, siltation, chemical contamination, and human disturbance have significantly reduced habitat quality by damaging the food supply. Changes in wetland isolation and stabilized water regimes are also eroding habitat quality. Acid rain is also another significant threat to the species due to its damaging effects on wetlands.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: special concern

IUCN Red List of Threatened Species: least concern

Global Long Term Trend: Decline of 30-70%

Comments: Long-term data not available rangewide. However, habitat trends suggest that substantial declines have probably occurred. The entire life cycle is dependent on wetlands, yet over half the original wetlands in the conterminous U.S. have been destroyed (Tiner 1984). Breeding Bird Survey (BBS) data (1966-1987) indicate a decline in the north-central U.S. (Hands et al. 1989, Brewer et al. 1991) and possibly in New England (USFWS 1987), due mainly to loss and degradation of wetlands. BBS data suggest a 2.4% annual decline in U.S. populations between 1966 and 1989, but no significant trends were evident for populations in the eastern U.S. or Canada; other sources suggest that declines have occurred in portions of New York and in southern New England, Pennsylvania, New Jersey, and Delaware (Gibbs and Melvin 1992).

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: Threatened by loss and degradation of wetlands due to drainage, filling, conversion to agriculture or recreational use, siltation, and pollution. The most serious factor limiting populations is availability of wetland habitat. The entire life cycle is dependent on wetlands, yet over half the original wetlands in the conterminous U.S. have been destroyed (Tiner 1984). The most serious losses have occurred among palustrine emergent wetlands, of which about 4.75 million acres (1.92 million ha) were lost between the mid-1950s and mid-1970s (Tiner 1984). Inland, freshwater wetlands, the most important nesting and wintering areas, are among the most threatened habitats (Tiner 1984). Larger wetlands (greater than 10 ha) may support large portions of regional nesting populations, and loss of these wetlands can be critical to populations in many areas. Small wetlands (less than five ha) may serve as important alternate feeding sites and as "stepping stones" during movements between larger wetlands, but receive no legal protection in most states. Habitat quality also may be limiting. Eutrophication, siltation, chemical contamination, and human disturbance may seriously reduce habitat quality, even at large protected wetlands. Eutrophication, caused by inflow of nitrates and phosphates from urban and agricultural areas, in combination with silting and turbidity, has damaged the aquatic fauna that serve as prey for endangered Eurasian bitterns in Great Britain (Day and Wilson 1978). Marshland invasion by purple loosestrife (LYTHRUM SALICARIA) and phragmites (PHRAGMITES AUSTRALIS) may substantially alter waterbird habitats in the northeastern U.S., but effects on bitterns have not been assessed. Acid deposition is a potential threat given the dependence on wetland habitats vulnerable to acidification, the high proportion of amphibians in their diet (Cottam and Uhler 1945), and the large numbers of bitterns and large proportion of the breeding range in regions receiving rainfall of reduced pH (the northeastern U.S. and central and eastern Canada). Amphibians are typically vulnerable to strong reductions in water pH (Freda 1985), and the Eurasian bittern avoids waters with pH less than 4.5 (Cramp 1977), probably because such waters lack amphibian and fish prey. However, American bitterns usually occupy habitats with substantial growths of emergent vegetation, even in more northerly parts of their range (DesGranges and Houde 1989; Gibbs et al., in press.). Such areas typically are of circumneutral pH and are chemically buffered against strong shifts in acidity. Little is known about the effects of contaminants. However, heavy metals, PCBs, and organochlorines have been found in tissues of a number of heron species (Fleming et al. 1983), despite bans on use of some of these chemicals (i.e., organochlorines) since the 1970s. Agricultural chemicals may have significant, indirect effects by entering wetlands via runoff from upland areas and reducing prey populations. Many of this bird's prey, including aquatic insects, crayfish, and amphibians, are vulnerable to agricultural pesticides. Wading birds are known to be moderately susceptible to oil toxicosis. A nematode parasite, EUSTRONGILIDES, contracted from small fish, can devastate wading bird populations, and thrives in waters polluted with nutrients and silt; bittern populations at wetlands and impoundments receiving stormwater and runoff from residential and agricultural areas may be particularly vulnerable to epizootics of Eustrongylidosis (P. Frederick, pers. comm.). Illegal shooting incidental to upland gamebird or waterfowl hunting has an unknown impact populations. Records maintained by the Massachusetts Division of Fisheries and Wildlife indicate that at least three bitterns were shot and killed on or adjacent to wildlife management areas in that state during pheasant hunting seasons between 1986-90 (B. Blodget and W. Easte, pers. comms.). Historically, hunting may have been a greater source of mortality than it is today. Audubon (1840) reported that American bitterns were "common" in markets of New Orleans in the early 1800s. Several of this bird's common names, such as Indian Hen and Meadow Hen, may reflect its popularity as food for native Americans and colonists. In Europe, illegal hunting has a significant impact on Eurasian bittern populations and has led to declines and prevented population recovery in many areas (Day 1981). Human disturbance in or along the margins of wetlands has unknown impacts on reproduction, feeding ecology, and site fidelity. In Great Britain, recreational boaters are thought to limit the availability of undisturbed feeding sites for Eurasian bitterns at protected wetlands (Bibby 1981). Draining, filling and disturbance of wetlands and environmental contamination (especially by chlorinated hydrocarbons) are suspected as causes of decline in Connecticut (Zeranski and Baptist 1990).

Restoration Potential: Because of extensive post-breeding dispersal (Cramp 1977), bitterns are able to colonize new habitats and persist as small, isolated populations. For example, the Eurasian bittern recolonized Great Britain in the 1940s, where it was extirpated in the 1870s, and now persists in six small populations (50 pairs total) located distantly from one another (Bibby 1981, Day 1981). Readily uses artificial wetlands created by impoundments at waterfowl refuges (Andrle and Carroll 1988, Gibbs et al. in press), a trait that could facilitate restoration of populations in regions where natural, inland freshwater wetlands have been destroyed (Connecticut, Rhode Island, central New York, New Jersey, and Maryland) or were scarce originally (central Pennsylvania and West Virginia). Also seems adaptable to a wide range of wetland habitats, ranging from margins of boreal lakes in Quebec (DesGranges and Houde 1989) to dense cattail marshes in New York (Andrle and Carroll 1988), and can thrive at wetlands of many types as long as suitable prey and adequate cover are available (Gibbs et al. in press). Information is too scarce, however, on the structure and potential growth rates of populations to speculate about the recovery potential.

Preserve Selection and Design Considerations: Wetland area is a consideration for preserve design because both occurrence (Brown and Dinsmore 1986) and abundance (Gibbs et al. in press, Gibbs and Melvin 1990) are greater on larger than smaller wetlands. Wetlands of 2.5 ha or more may support nesting; smaller wetlands may serve as alternate foraging sites (Gibbs and Melvin 1992). In Maine, inhabited wetlands from less than one to greater than 25 ha in size, but were more abundant in larger than smaller wetlands, and preferred impoundments and beaver-created wetlands to wetlands of glacial origin (Gibbs et al. in press, Gibbs and Melvin 1990). Eaton (1914) suggested that there were occurrences in New York at marshes of less than four ha. In Iowa, Brown and Dinsmore (1986) observed individuals only on wetlands of greater than 11 ha and suggested that occurrences at wetlands was possibly area-dependent. A minimum area of 2.5-5 ha is therefore suggested as being sufficient to support nesting activity (see Eaton 1910, Brown and Dinsmore 1986, Gibbs et al. in press). Smaller wetlands adjacent to large wetlands used for nesting may serve as important, alternate foraging sites for these birds, which are seen regularly flying between wetlands during the nesting season in Maine (J. Gibbs, pers. obs.). Vegetative features of wetland preserves should include a high diversity of vegetative life forms and an abundance of emergent vegetation well-interspersed with patches of open water and aquatic-bed vegetation. Water levels should be less than 10 cm deep (Fredrickson and Reid 1986). Retaining dense, woody riparian vegetation may provide a visual barrier that reduces human disturbance of nesting bitterns and also buffers a wetland ecosystem against upland runoff that may contain silt, pesticides, and other contaminants (Gibbs and Melvin 1992).

Management Requirements: Wetlands used for breeding need to be protected from chemical contamination, siltation, eutrophication, and other forms of pollution that harm these birds or their food supplies. Day and Wilson (1978) emphasized that merely preserving habitats for endangered populations of Eurasian bitterns is not adequate to ensure their longterm viability; management of vegetation and monitoring water quality at protected areas also is required.

Vegetative features of preferred habitats represent a particular stage of wetland succession. Wetland managers therefore need to periodically reverse vegetative succession while maintaining suitable habitats nearby to serve as alternate nesting areas during wetland manipulations. The concentration of both nesting and overwintering populations at protected and managed wetlands such as state and national wildlife refuges (Andrle and Carroll 1988, Root 1988) emphasizes the need to develop and implement beneficial habitat management procedures. Minor alterations of existing management schemes could greatly improve nesting habitat. Where littoral vegetation is scarce, moist soil plant management (Fredrickson and Taylor 1982) provides a cost effective method involving water-level manipulation to reestablish and promote growth of dense stands of emergent vegetation.

Complete drawdowns should be avoided so that populations of small fish, amphibians, and dragonfly larvae, which make up a large part of the diet, are conserved for the following season. Slow, rather than rapid, drawdowns emulate natural water recession patterns, concentrate foods, and help prevent oxygen depletion (Fredrickson and Reid 1986). Drawdowns can be used to create favorable water levels (less than 10 cm deep, Fredrickson and Reid 1986) for foraging. Liming and fertilizing dikes and adjacent fields can increase productivity and raise the pH of many nutrient-poor, acidic wetlands in the northeastern region (Jorde et al. 1989). Control of infestations of purple loosestrife and phragmites may improve habitats in many northeastern states.

Management Research Needs: Develop standardized methodologies for population monitoring in the northeastern U.S.

Conduct surveys to determine abundance and distribution in the northeastern U.S.

Monitor trends in populations and habitat availability in the northeastern U.S.

Conduct a detailed, autecological study that examines basic features of the breeding biology of the species, including diet, home range, mating systems, ability to renest, sources and rates of mortality in adults, juveniles, nestlings, and eggs, and juvenile dispersal patterns and philopatry. This information could be gathered through radio-telemetry and banding studies.

Evaluate habitat requirements, including the vegetative characteristics, water quality, and minimum area of wetlands used by nesting, migrant, and overwintering birds. Also, evaluate effects of riparian zone management on wetland use.

Identify migration routes, major stopover sites, and major overwintering areas.

Examine the effects of contaminants, parasites, diseases, predation, water pollution, acid rain, human disturbance, and severe weather on populations.

Develop wetland management strategies that benefit nesting and migrant birds. Because the distribution of nesting birds is closely tied to protected wetlands at state and national wildlife refuges in many parts of the Northeast, assess the long-term viability of these sites as core-breeding areas for regional populations.

Monitor contaminant levels in adults and eggs in industrialized and agricultural regions of the northeastern U.S.

Evaluate the effects of marsh invasion by phragmites and purple loosestrife.

Global Protection: Few to several (1-12) occurrences appropriately protected and managed

Comments: Probably adequately protected in many wetlands, such as those managed for waterfowl production.

Needs: Preservation of wetland habitats, particularly large (greater than 10 ha), shallow wetlands with dense growths of robust emergents, is the most urgent protection need. Protect habitat through land purchases and easements.

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Stewardship Overview: Breeds and overwinters in freshwater wetlands with emergent vegetation and shallow water. Widely distributed across the Northeast, but little is known about population size, although trends appear to be stable. Loss and degradation of wetlands is the most serious threat. Frequents artificial impoundments at managed wildlife areas during the breeding and wintering seasons, thereby providing a good opportunity to manage habitat specifically for this bird. Slow drawdowns can be used to create foraging areas and to encourage dense stands of emergent vegetation. Standardized surveys should be conducted across the region to determine abundance and more accurate population trends of this as well as other secretive wetland birds. Point-counts using tape-recorded vocalizations could be used to survey wetlands across the region.