Delta Marsh (MB001)
Portage la Prairie, Manitoba
Description du site
Delta Marsh is a large wetland comprised of wide shallow bays, sloughs and meadows. It stretches westward from St Laurent to Lynch Point along the southern end of Lake Manitoba. The marsh is separated from the lake by a sand ridge covered with deciduous trees including green ash, Manitoba maple, hackberry, willow and cottonwood. The hackberry stand is the northernmost location for this species within Manitoba. The ridge and associated deciduous forest acts as a natural migrational corridor for landbirds migrating to and from the boreal forest and aspen parklands to the west of Lake Manitoba. The 17,000 ha marsh is one of the largest of several marshes in the Lake Manitoba basin.
Oiseaux
Large numbers of both diving (Canvasback, Redhead, Lesser Scaup) and dabbling (Mallard, Gadwall, American Wigeon, and Northern Pintail) ducks stage in the marsh each fall. For example, a total of 27,000 Mallard were recorded here in fall 1991 and 12,000 Lesser Scaup in April 1971. In 1974, 22,000 Canvasback were observed here during fall. Up to 100,000 waterfowl have been detected during aerial surveys. The number of geese using the site has increased from historic levels with Canada Geese and Snow Geese staging here in large numbers during both spring and fall migration, including an estimated 1,000,000 Snow Geese in 1995.
Delta Marsh also provides staging and breeding habitat for migratory shorebirds, although concentrations vary depending on water levels. More than 1% of the estimated global population of Semipalmated Plover (1,905) were counted here in 2016. Ruddy Turnstones congregate in large numbers, 1,000 being counted on June 2, 1993. On a single day in August 2016, 3,598 Semipalmated Sandpiper and 1,163 Least Sandpiper were observed here.
Large numbers of landbirds also make use of the site. Some indication of the significance is reflected in the banding totals reported by the Delta Marsh Bird Observatory. Between 1995 and 1997, the number of landbirds banded in a single season ranged from 7,500 to more than 9,000 individuals suggesting even higher (much higher) totals of birds migrating through or breeding in the area. In 1996, a total of 3,000 Yellow Warblers and 1,100 Tennessee Warblers were banded. More than 300 individuals of several other landbird species (Yellow-rumped Warbler, American Redstart, White-throated Sparrow, Least Flycatcher, Ruby-crowned Kinglet, Common Yellowthroat, and Song Sparrow) were also regularly banded each season. Up to 50,000 Tree and Bank swallows have been estimated during daily censuses.
Concentrations of over 1000 Western Grebes during migration (1996) and over 1000 pairs breeding (1979) have been counted here. A further study estimated that there were 1,314 Western Grebe nests in nine colonies in 2009 and 1,428 nests in eight colonies in 2010. The number of nests dropped off after 2011 following swelling of the marsh during a flood event on Lake Manitoba.
More than 1,000 Franklin Gulls and 5,000 Ring-billed Gulls have also been observed. Large concentrations of herons (Great Egret, Great Blue Heron and Black-crowned Night Heron) are present in the marsh interior.
Enjeux de conservation
Approximately 11,275 ha of Delta Marsh itself is in public ownership as provincial Crown lands administered by the Wildlife Branch of Manitoba Sustainable Development. This provincial crown land is designated as Heritage Marsh. A further 6,782 ha Is part of the Lake Francis Wildlife Management Area. An additional 2,000 ha of this area is protected as a game bird refuge and 7,700 ha as public shooting grounds. The remaining land is under private ownership.
The Delta Marsh is a major waterfowl staging area and was designated as a Wetland of International Importance in 1982 under the Ramsar Convention. Delta Marsh has a long association with research and monitoring by different groups, although the facilities for much of this work have either closed down or are in the process of changing hands. The Delta Waterfowl Research Station, which controls 1,600 ha of the marsh, has been conducting waterfowl studies since 1938. A second research station, the University of Manitoba Field Station, conducted landbird research between 1964 and 2011. In 1995, the Delta Marsh Bird Observatory was established as part of the Canadian Migration Monitoring Network to monitor migration at these sites during spring and fall migration. Due to the loss of the field station following flooding in 2011, the Delta Bird Observatory moved to Oak Hammock Marsh in 2016.
Sections of the west portion of the marsh are periodically flooded by the Portage Floodway (a flood control structure), causing excessive siltation and vegetation growth. Threats to the surrounding area include pressures to develop additional cottage sites and recreational facilities on nearby Lake Manitoba beaches.
Management plans for water control have been proposed by the province in 1978 and Ducks Unlimited Canada in 1981.
Catégories ZICO Habitats Usages Menaces Potencielles ou Existantes Status de Protection
