Each of the bird species described in this manual, with the exception of the American Coot, is secretive and more often heard than seen. This generally secretive nature, combined with an affinity for marshy, inaccessible habitats, has resulted in a very limited understanding of the biology and habitat use of most rails and bitterns. Their elusive lifestyle also means it is very challenging to monitor bittern and rail populations.
Rails (Rallidae) have been identified as a family of birds containing more species at risk of extinction globally than would be expected by chance (Bennett and Owens 1997). The decline of American Bittern populations in some states has been clearly associated with the loss of wetlands (Gibbs et al. 1992a). Eutrophication, siltation, chemical contamination and human disturbance have also affected habitat use by many marsh birds (Gibbs et al. 1992a).
This objective of this manual is to standardize marsh bird surveys in British Columbia. It was also developed with the intention of making these surveys comparable to marsh bird surveys in other North American locations. The Marsh Monitoring program of eastern Canada provided useful protocols in this respect. This program was established by Canadian Wildlife Service (CWS) and Bird Studies Canada (formerly Long Point Observatory) to monitor marsh birds and other associated fauna in southern Ontario and the Great Lakes area. In addition, these two organizations are currently working together with the U.S. Fish and Wildlife Service/ Geological Survey, and others to design a protocol applicable on a national or continental scale (R. Weeber, Aquatic Surveys Coordinator, Bird Studies Canada, pers. comm.). However, at the time this manual was being prepared, such a monitoring program did not yet exist.
This section summarizes the distribution and ecology of bitterns and rails that may be found in B.C. These include American Bittern (Botaurus lentiginosus), Virginia Rail (Rallus limicola), Sora (Porzana carolina), and American Coot (Fulica americana). Also included in this survey standard are descriptions of Least Bittern (Ixobrychus exilis), considered casual in summer (see Glossary), and Yellow Rail (Coturnicops noveboracensis) whose occurrence is considered hypothetical in B.C. (Campbell et al. 1990b). Given that several good sightings have been made since the publication of Campbell et al.(1990b), it might be more appropriate to consider the occurrence of the Yellow Rail as accidental (Table 1).
Table 1. Species covered in the bitterns and rails inventory group.
|
Common name |
Scientific name |
Species code |
Status in B.C. (1997) |
|
American Bittern |
Botaurus lentiginosus |
B-AMBI |
Blue |
|
Least Bittern |
Ixobrychus exilis |
B-LEBI |
Yellow |
|
Yellow Rail |
Coturnicops noveboracensis |
B-YERA |
Accidental |
|
Virginia Rail |
Rallus limicola |
B-VIRA |
Yellow |
|
Sora |
Porzana carolina |
B-SORA |
Yellow |
|
American Coot |
Fulica americana |
B-AMCO |
Yellow |
Bitterns and rails are generally secretive, making them very difficult to locate and observe. Thus, it is equally difficult to conduct an inventory of this group of birds. Rails are generally more often heard than seen. Virginia Rail and Sora are the most abundant rails in North America and will, within their range, occur in most marshes where emergent vegetation exists (Capen and Low 1980). The provincial distributions of other species, such as Yellow Rail and Least Bittern, are unknown, and therefore information derived from future RIC surveys will help to determine their occurrence and distribution within the province.
Biologists conducting surveys for bitterns and rails should be familiar with the life history and habitat characteristics of other wetland birds. There are several other species (including hypothetical and casual occurences) that share similar behaviours and/or similar habitats with bitterns and rails in B.C. These include the Great Blue Heron (Ardea herodias), Green (Green-backed) Heron (Butorides virescens), Little Blue Heron (Egretta caerulea), Great Egret (Ardea albus), Cattle Egret (Bubulcus ibis), Snowy Egret (Egretta thula), Black-crowned Night-Heron (Nycticorax nycticorax), White-faced Ibis (Plegadis chihi), and possibly Black Rail (Lateralus jamaicensis). None of these species are discussed further in this document, but it is expected that the methods suggested for this inventory group could be applied to at least some of these additional species. Awareness of life histories of all marsh birds will help to ensure that the survey activities for the target inventory group do not affect the behaviour of non-target species. Specific survey methods for the Great Blue Heron are covered in the Resources Inventory Committee (RIC) manual No. 8 (Resources Inventory Committee 1998).
The species accounts below include the major citations of life history descriptions such as found in the American Ornithologists' Union's "Life Histories of North American Birds" or species accounts in Tacha and Braun (1994). Individuals interested in conducting intensive studies of these species should refer to these publications for greater detail.
The American Bittern is a medium-sized (60-80 cm long, 370-500 g) heron with cryptic brown plumage, a stout body and neck, and relatively short legs. It has a long black stripe that begins below its eye and extends down the side of its neck. The plumage of males and females has similar colouring, but males are slightly larger. Flight is relatively ungraceful, characterized by long wingbeats (Gibbs et al. 1992a).
American Bittern calls carry long distances relative to the other species included in this manual. Calls include "pumping", a low and resonant 3-syllable pump-er-lunk or dunk-a-doo repeated 1-10 times in succession (Gibbs et al. 1992a). When flushed, they will give a hoarse kok-kok-kok (Peterson 1990; Gibbs et al. 1992a), or a nasal hoink (Gibbs et al. 1992a). Although calling can occur day and night at the height of the breeding season, most vocalizations occur early in the breeding season, and generally in the dim light at dawn and dusk.
American Bitterns prefer vegetated edges and shorelines of wetlands that are dominated by tall, emergent vegetation (i.e. taller than the bird itself). They have been found in wetlands of all sizes, but appear to prefer impoundments or beaver-created wetlands (Gibbs et al. 1992a). Use of wetlands appears to be restricted to those portions with water which are shallow enough to stand in (less than 10 cm).
American Bittern nests are platforms of reeds and other vegetation usually 25-40 cm in diametre and 15-40 cm high (Campbell et al. 1990a; Gibbs et al. 1992a). They are usually well concealed within dense emergent vegetation such as cattail and bulrush. Gibbs et al. (1992a) describe nests occurring over water ranging from 5 to 20 cm deep; however, nests in B.C. have been built above water up to 36 cm deep (Campbell et al. 1990a). Bitterns will occasionally nest on dry ground in dense vegetation greater than 30 cm tall in grasslands adjacent to wetlands (Gibbs et al. 1992a).
American Bitterns are "stand-and-watch" foragers. Their prey includes water insects, small fish, amphibians, snakes, and small mammals. Bitterns will hide themselves in the vegetation and assume a "bittern" stance when approached. This involves pointing their bill skyward, stretching the body vertically, compressing their feathers against the body, and swaying in the breeze (Gibbs et al. 1992a).
American Bittern is listed by the B.C. Conservation Data Centre (CDC) as common at the national scale, but provincially rare to uncommon and potentially susceptible to large scale disturbances. It is on the 1997 Provincial Blue list in B.C.
There is little information about movement and migrations of American Bitterns. They begin arriving at breeding marshes and wetlands in early spring (March - April) (Gibbs et al. 1992a). Generally speaking, they arrive later at more northerly locations. Bitterns have arrived in the Chilcotin-Cariboo during the second and third weeks of May, and have reached the Peace Lowlands in late May (Campbell et al. 1990a). Most Bitterns leave the breeding marshes in late September and early October (Campbell et al. 1990a), although fall migration may begin as early as late August in northern B.C. and may last as late as November. Major river systems and coastal belts are probably important for migrational movements (Gibbs et al. 1992a). Small numbers of American Bitterns winter in marshes in the Fraser Lowlands and southeastern Vancouver Island (Campbell et al. 1990a).
Territorial American Bitterns call infrequently, except for a short period of time each morning near at dawn and dusk, or in response to conspecific call playback (Gibbs and Melvin 1992; Sauer et al. 1997). In a study of statistical power, Gibbs and Melvin (1997) conducted multispecies call playback surveys of grebes, rails, soras, and bitterns in Maine. The power to detect population trends was lower for the American Bitterns than for any other species. Bitterns appear to be particularly unresponsive in inclement weather conditions. However, the researchers speculate that the problem could be partly compensated for by conducting surveys earlier in the season, and in absolutely favourable weather conditions.
The Least Bittern is a small (28-36 cm, 80 g), thin bird with a greenish-black crown, back and tail, and a thin yellow bill. In flight it can be confused with a rail because of its dangling feet and weak, short flight pattern. Plumage is dimorphic; females have a more purple-chestnut or brown crown and back, while males appear blacker. The neck of the female is also darkly streaked (Gibbs et al. 1992b; Sauer et al. 1997).
All calls are generally soft and barely audible (Johnson et al. 1981), Least Bitterns will make a variety of vocalizations, including the male's low, dove-like coo-coo-coo (Gibbs et al. 1992b) and an ank-ank when flushed (Gibbs et al. 1992b).
Least Bitterns are found in freshwater and brackish marshes with dense, tall growth of aquatic or semi-aquatic vegetation interspersed with clumps of woody plants and open water. They are not associated with open water, sparse or short vegetation, or muddy openings (Gibbs et al. 1992b). A few Least Bitterns have been recorded in summer in the central southern interior and in a brackish marsh on the southern mainland coast of B.C. (Campbell et al. 1990a). Least Bittern appear to prefer deeper water habitats for nesting and foraging than do American Bitterns (Gibbs et al. 1992b). They feed on aquatic insects, small fish, amphibians, and some small mammals.
Least Bitterns build there nests 15-76 cm above relatively deep (8-96 cm) water. The nest platform may be made from stems of surrounding vegetation, folded over with other vegetation placed on top. Nests are 15-20 cm in diametre, 5-12 cm thick, and have a canopy. They are often found less than 10 m from open water, along channels, or muskrat trails (Gibbs et al. 1992b).
The Least Bittern is on the 1997 Yellow list for B.C.
Least Bitterns arrive at breeding marshes in early April to late May and leave again to return south in late August through September. Few birds are found north of the Gulf States past mid-October (Gibbs et al. 1992b). Specific movement and migration dates in B.C. are unknown.
There is generally a lack of information on survey techniques for Least Bittern. Gibbs and Melvin (1993) found that Least Bittern response rates to call playback surveys in Maine were lower than American Bittern, Pied-billed Grebe (Podilymbus podiceps), Virginia Rail and Sora. The authors suggest that this could have been the result of a fewer number of Least Bitterns being present; however their actual abundance relative to the other species was unknown.