The Lower Mackenzie River Islands IBA site starts at Fort Good Hope, Northwest Territories, and continues down the Mackenzie River for 270 kilometres to where the Tree River joins the Mackenzie. The numerous river islands found here are composed of sedimentary deposits overtop of Devonian bedrock. Spring floods result in sand bars and shorelines of sand, mud and willow trees around low-lying islands. Away from the periphery of the islands, forests of mature white spruce and balsam polar grow. In winter the islands are the preferred habitat of moose. The poplar stands provide cover and the willow trees are an excellent food source.
Observations made in the early 1970s suggest that most of the Western Central Flyway population of Lesser Snow Geese migrate through the lower Mackenzie River in the spring. This, somewhat ill-named population is the westernmost breeding population of Snow Geese, breeding in Alaska and the western Canadian arctic. In the mid-1970s, the numbers of geese in this population was about 169,600, but has now almost reached the half million mark. In 1972, 63,900 Snow Geese were recorded on the river in late May. This is over a third of the Western Central Flyway Snow Geese population of the time. In 1973, a May 14 aerial survey recorded 13,800. Timing of the surveys is crucial since, although the use of the river by geese is intense, it is short-lived; thus one survey date in a year may not coincide with peak migration. Conversely, the numbers of geese using the area in the spring are also thought to be quite variable, which may also account for the variation between years. Although there is no recent information on bird use of the area, since the area downstream from Fort Good Hope is known to be a traditional stopover point, it is assumed that the geese are still using the area. The geese, which arrive in the area in early to mid-May, feed along the open shorelines of the islands.
Migrations of Tundra Swans and other waterfowl using the lower Mackenzie River are similarly short-lived but immense. For instance, as many as 112,800 waterfowl were recorded along this stretch of river on May 25, 1972, but four days later fewer than 10,000 remained. The same year in May, up to 3,250 Tundra Swans were counted along a stretch of river that starts at the downstream end of this site (Tree River) and goes upstream beyond the site to Norman Wells. This number of swans represents about 1.5% of the North American population.
BirdLife International (2020) Important Bird Areas factsheet: Lower Mackenzie River Islands. Downloaded from http://www.birdlife.org on 08/07/2020.