Douglas Marsh is located east of the city of Brandon Manitoba; the Trans-Canada Highway runs along the north border and the community of Shilo lies to the south. This large and shallow fen, which acts as a catchment basin for the surrounding agricultural land, has little open water except at its western end. Sedges and grasses are the dominant vegetation types, but two gentians that are rare in Manitoba, Felwort and Star Gentian, are also found here. On the eastern side of the marsh lies the willow-shrub edge of the Carberry Sandhills.
Birders and guided bird groups come to Douglas Marsh to see Yellow Rails where the extensive fens of western side of Douglas Marsh hold very large numbers of the nationally vulnerable species. This rail is one of the most secretive species of birds, and so accurate surveys are difficult. Nonetheless, in 1995 a minimum of 500 pairs were thought by some to breed at Douglas Marsh, representing 11.6% of the global population. It should be noted that this number was arrived at by extrapolation. Another observer recorded 108 calls in a five-minute period in June, 1993. Although a precise estimate is not known, most observers agree that this site is significant for Yellow Rail and indeed may hold the largest colony of Yellow Rails south of the Hudsons Bay Lowlands.
Several other marsh and grassland species are known to occur in the marsh. Virginia Rail and Sora both nest here and LeContes Sparrow and Nelsons Sharp-tailed Sparrow are also regularly encountered in large numbers during the breeding season. Sedge Wrens are found in the hundreds and nest throughout the marsh, and Mallards are common breeders.
Natural elements such as drought and succession of plant species all have an impact on this marsh. Factors caused by humans that are or could affect the marsh include: an increase in agriculture, the spraying of herbicides, fire management, ecotourism, highway expansion and overgrazing by cattle. Some of these actions could severely impact the functioning of the marsh ecosystem, and the survival of the Yellow Rails. For example, the development of Highway #340, which runs through the site, is the major threat to bird habitat and endangered plant species; the Highways Department has obtained an environmental license to proceed with this highway. Ecotourism is also a threat since occasionally people trample rail habitat and nest sites. When making development decisions, care must be taken to maintain the natural features of the marsh, and to minimize the disturbance of the birds.
Additionally, beavers have been known to block culverts, which resulted in the flooding of Yellow Rail habitat. Since the rails need shallow water less than 20 cm deep, even moderate flooding of this kind can make habitat unsuitable.IBA Criteria Habitats Land Uses Potential or Ongoing Threats Conservation Status