Oak Lake/Plum Lakes Area (MB011)
Oak Lake, Manitoba
Altitude 411 - 430m
Description du site
Oak Lake, and the associated Plum Lake, are located in southwestern Manitoba, southwest of the town that shares its name. The lake is surrounded by a vast marshland about four times its size that is fed by Pipestone Creek and drained by Plum Creek. This extensive lake and marsh system and the surrounding area, generally in very flat terrain, contain a tremendous diversity of habitat. There is a blend of rivers and streams, grasslands, deciduous woods, willow scrub, and rocky areas, along with cultivated agricultural lands. Grasses and sedges border the wetland, and remnants of undisturbed native prairie can be found. Extensive dykes surround Oak Lake, which is artificially regulated by a water control dam. Close to the town of Oak Lake there are extensive sand dunes that are heavily treed with Bur Oak, Trembling Aspen, Creeping Juniper. Located slightly further north is the Assiniboine Valley, which has a valley wall exceeding 100 m in height.
In keeping with its vast habitat diversity, this site hosts a large diversity of birds, during both the breeding season and fall migration. A large colony of Franklins Gulls nest in the marsh. Over 30,000 pairs of birds, roughly equivalent to 8.6% of the estimated global population, have been recorded. Both Eared Grebes and Black-crowned Night Herons are found here in nationally significant numbers; 4.3% and 6.3% of their estimated Canadian populations respectively.
Huge numbers of waterfowl stop at Oak and Plum Lakes in fall migration. Species reported in significant numbers during fall migration include: Tundra Swan (1.3% of the estimated North American population); Canada Goose (2.8% of the estimated Short-grass Prairie population); Snow Goose (between 1 and 3% of the estimated Mid-continent population); and Greater White-fronted Geese. For the latter species, numbers of migrants varies considerably from year to year - over 3,400 were recorded recently, but 27,000 were recorded in 1968. Similarly, significant peak numbers of Mallards, Lesser Scaup, and American Coots have been recorded in some years. Other species that can be seen in large numbers in the fall include, Bald Eagles (135+), Golden Eagles (30+), and Sandhill Cranes (3,300+).
During the breeding season landbird diversity is high. Some of the provinces highest concentrations of Eastern Bluebirds and Mountain Bluebirds are found here - 35 pairs and over 250 pairs respectively. In 1998, 11 pairs of the nationally threatened Loggerhead Shrike (western subspecies) were found here. Under optimal conditions during the breeding season, birders can daily record Nelsons Sharp-tailed Sparrow, Le Contes Sparrow, Grasshopper Sparrow, and Bairds Sparrow along the west side of the lake. Burrowing Owl and Ferruginous Hawk are two raptors known to breed in the region.
Enjeux de conservation
There is great pressure to develop the Oak Lake area through more intensive agricultural practices. Ongoing disagreement exists over water use and wetland management, including whether or not to drain parts of the area, and what the ideal water level should be. Species such as the Eared Grebe that are not tolerant of water level changes are particularly susceptible to drainage of suitable nesting habitat. However, an increasing number of properties in this area are being purchased and put into wildlife conservation use.
Menaces Potencielles ou Existantes
Status de Protection