Netley-Libau Marsh is situated at the south end of Lake Winnipeg, where the Red River branches several times and empties into the lake. Wave action on Lake Winnipeg, particularly due to strong wind-assisted tides, has produced a small beach ridge at the lakes south end, which acts as a barrier separating parts of Netley-Libau Marsh from the lake. The Red River is an important force of change in the large network of wetlands found here. Due to its history of frequent flooding, the route of the main channel of the river has changed numerous times. The area is very flat, and consists of many small bodies of water connected by channels and is interlaced with fingers of grassland, trees and shrubs.
Netley-Libau Marsh is best known for its tremendous concentrations of southward-migrating birds. Numbers of geese and ducks on some occasions exceed 100,000 during fall migration. A little earlier in the year, at least 25,000 moulting ducks are found in the area. Red-winged and Yellow-headed blackbirds congregate here in late autumn in numbers exceeding 100,000. As well, at the beginning of the fall migration in August, swallows are found here in the thousands.
In addition to the numerous species that stopover at the site during fall migration, several bird species breed at this site in significant numbers. Franklins Gulls nest in large colonies within the marsh, in numbers exceeding 4,500 pairs. This represents at least 1.3% of the North American population, based on upper level population estimates. In the late 1970s, 325 Forsters Tern nests were recorded in the marsh (about 1.5% of the global population). In addition, over 100 pairs of Black-crowned Night-Herons have been observed nesting in the marsh, which account for 2% of the estimated national population. Species that breed in large, though not significant numbers at the site include the Eared Grebe (100+ pairs) and the Western Grebe (125+ pairs). At least twelve species of ducks breed here mostly dabbling ducks.
The portion of the site around Hardman Lake, which is between the main channel and west channels, is the Netley Marsh Game Bird Refuge, created in 1966 to improve hunting by providing a refuge area for migratory game birds; the whole Netley-Libau Marsh site has been designated as a Manitoba Heritage Marsh. Recreation is the main use of the inner delta, while the main channels see much use by sport fishermen. This occasionally leads to disturbance of nesting birds. An important commercial minnow fishing industry occurs here.
Because the water levels of Lake Winnipeg are regulated by Manitoba Hydro, the physical structure of the marshes has been altered, leading to the loss of wetland habitat. Part of this change can be seen in the number of water bodies comprising the marsh: in 1960 there were 50 individual waterbodies, whereas in 1980 the number had decreased to 17. The control and maintenance of water levels also means that natural drawdowns, which encourage new plant species, are eliminated. Large floods that sweep through the Netley Marsh are a natural phenomenon that occur from time to time. These floods tend to discourage development such as urbanization and agriculture.
Other threats to the area include Purple Loosestrife, this site having the provinces largest infestation, and carp, which destroy marsh vegetation thereby removing food sources for some duck species. Rainbow Smelt and Zebra Mussels are also concerns at this site.Catégories ZICO Habitats Usages Menaces Potencielles ou Existantes Status de Protection
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