IBA Thomsen River
Banks Island, Northwest Territories
Site Summary
NT043 Latitude
73.903° N
119.812° W
0 m
660.99 km²
deciduous woods (boreal/alpine), scrub/shrub, tundra, sedge/grass meadows, rivers/streams, open sea
Land Use:
Nature conservation and research
Potential or ongoing Threats:
Disturbance, Oil slicks
IBA Criteria: Globally Significant: Congregatory Species
Conservation status: Migratory Bird Sanctuary (federal), National Park
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Site Description
The Thomsen River is located in north-central Banks Island, in the western Arctic. The site covers the river from its mouth at Castel Bay to a point about 60 km upstream. The river flows through a broad valley surrounded by low rolling hills. These hills are dissected by gullies and underlain by sandstone and shale. The river empties into Castel Bay with the adjacent landscape being characterizand by deeply cut badland topography. Polar desert and arctic tundra communities dominate the vegetation, with the main types being dwarf shrub, willow-sedge and lichen-legume tundra. Extensive wet sedge meadows are found in the valley bottom of the river. A polynya exists in Mclure Strait and open water can appear as early as January or February. Muskoxen are common year-round, while Peary Caribou migrate north in late spring, moving to calving grounds in the northeast and northwest parts of the island. Arctic Foxes are common and Polar Bears are occasionally spotted along the northern coast.

As many as 5,000 moulting Black Brant (subspecies nigricans) have been observed in the Thomsen River valley and around Castel Bay during late summer. This number exceeds 3% of this subspecies estimated population, and is represents over 1% of the North American Brant population.

During the late summer, up to 25,000 moulting Lesser Snow Geese have also been reported in the Thomsen River valley. However, it is unknown how consistently the geese use this area for moulting year to year. Surveys in the mid-1970s recorded a maximum of only 1,200 birds in early August, while later reports in 1988 and 1989 found that numbers varied from several hundred to none. Moulting Canada Geese have also been recorded along the river. Since the formation of Aulavik National Park in 1994, additional breeding bird surveys have b een completed. A total of 43 nesting species have been recorded, of which Lapland Longspurs are most common.

IBA Criteria
SpeciesT | A | I Links Date Season Number G C N
Brant 1975 OT 5,000
Note: species shown in bold indicate that the maximum number exceeds at least one of the IBA thresholds (sub-regional, regional or global). The site may still not qualify for that level of IBA if the maximum number reflects an exceptional or historical occurrence.
Conservation Issues
Moulting geese are generally very susceptible to disturbance. Although seismic exploration has occurred place throughout the site in the past, the formation of Aulavik National Park in 1994 should restrict such activities in the future.

In addition to being within Aulavik National Park, the Thomsen River is also within the Banks Island Bird Sanctuary No. 2.

The IBA Program is an international conservation initiative coordinated by BirdLife International. The Canadian co-partners for the IBA Program are Birds Canada and Nature Canada.
   © Birds Canada