IBA criteria met: A4i, A4iii (2008)
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Area: 6,700 ha
Site description (baseline)
Situated approximately 30 km north of Winnipeg, Oak Hammock Marsh is a man-made freshwater marsh restored from a remnant of the former St. Andrews Bog and marginal agricultural land. Beginning in 1967, Manitoba Natural Resources, Ducks Unlimited, the federal government, volunteer conservation organizations and local landowners began the restoration. It is a very flat area characterized by a series of dykes, water basins and artificial islands, which are managed to provide wetland habitat. Water enters the wetland by artesian wells and through Wavey Creek, then flows south through the man-made basins, and empties out of the marsh into Parks Creek, a tributary of the Red River. The area is about one-third wetlands and two-thirds uplands. The vegetation is a mix of grasses, sedges, and other herbaceous plants Phragmites communis, cattails and bulrushes are among the more common plants. The uplands contain substantial amounts of lure crops that are managed for waterfowl, as well as the only treed area, a small bluff of oaks and aspens in the southeastern corner.
Oak Hammock Marsh is perhaps Manitobas best- known natural area. At least 106 species of birds have bred and 296 species in total have been recorded in this relatively small area. Large concentrations of marsh birds are one of the reasons for its importance. About 5,500 pairs of breeding Franklins Gulls have been recorded, representing at least 1.6% of the North American population (based on upper level population estimates). A colony of as many as 70 pairs of Black-crowned Night Herons represents approximately 1.4% of the Canadian population. Other species of interest that are reported occasionally (and may breed) at Oak Hammock include Least Bittern, Yellow Rail and Red-headed Woodpecker (all nationally vulnerable species). In the spring, large numbers of shorebirds stop at Oak Hammock. Peak numbers recorded are 16,759 birds in 1981. Counts made of single species suggest that this number is low. For instance, 7,000 White-rumped Sandpipers (1.8% of the global population), 5,000 Short-billed Dowitchers (1.6% of the global population), 600 Hudsonian Godwits (1.2% of global population) and 5,400 yellowlegs have been recorded here. Note that these percentages are uncertain due to limited data on populations of northern-breeding shorebirds. The numbers of these shorebirds only occasionally reach the levels indicated, and are largely dependent on the timing of the lowering of water levels in the cells and the availability of suitable habitat outside of the site (causing the shorebirds to disperse more).
During fall migration many species use Oak Hammock Marsh as a stopover site. Numbers in excess of 250,000 Lesser Snow Geese have been observed, which accounts for about 8% of the Hudson Bay (Mid-continent) population. An impressive 200,000 Canada Geese have been recorded at the site. As many as four subspecies were mixed in the flocks (Giant, Eastern Prairie, Short Grass Prairie and Tall Grass Prairie) with each one almost certainly surpassing their respective continental thresholds. Mallard have been recorded in numbers as high as 70,000, such as on November 14, 1993. Coots are also extremely well represented here, with 2.2% of the North American population, or over 30,000 individuals having been found.
Many other species are found in abundance including nesting Eared Grebes, and in autumn, Yellow-headed and Red-winged Blackbirds and Bank Swallows.
BirdLife International (2023) Important Bird Area factsheet: Oak Hammock Marsh WMA. Downloaded from http://datazone.birdlife.org/site/factsheet/11135 on 28/05/2023.