Pring versions of Polar Bear Den Sites (1.4 meg file) and Polar Bear Denning Habitats (930 kb file) are available in PDF format. (PDF information.)
Female polar bears den during the winter they give birth to young. Other polar bears do not
den, but are active year-round.
The pink dots on this map show the distribution of maternal dens occupied by radio-collared polar bears
between 1981 and 2000 on the mainland coast of Alaska and Canada. The collared bears are a subset of the total number of bears that use this area. Tracking of the collared bears identified 53 dens along
the mainland coast, 26 (50%) of which were within the bounds of the Arctic National Wildlife
Refuge. Twenty-two of the 53 dens (42%) were within the bounds of the 1002 area.
Other dens have been located on the Alaska north slope since the turn of the century, but
these observations cannot be considered to have an unbiased distribution since visual searches
only locate dens in areas where investigators look. However, the dens shown on this map
represent an unbiased estimate of denning distribution because the radio-collared bears led
investigators to the den sites. Statistical tests (see below) confirmed that the distribution
of these dens was not biased by the distribution of the sampling (radio-tagging) efforts.
This information was collected from: 1. Arctic 46:246-250, Human disturbances of denning polar
bears in Alaska; 2. Journal of Wildlife Management 58:1-10, Polar bear maternity denning in the
Beaufort Sea; and 3. Amstrup (unpubl. data).
Additional information is available in:
Amstrup, S.C. 2002. Movements and population dynamics of polar bears. Pages 65-70 in D.C. Douglas, P.E. Reynolds, and E.B. Rhode, editors. Arctic Refuge coastal plain terrestrial wildlife research summaries. U.S. Geological Survey, Biological Resources Division, Biological Science Report USGS/BRD/BSR-2002-0001.
The information on this sheet is from:
Durner, G.M., S.C. Amstrup, and K.J. Ambrosius. 2006. Polar bear maternal den habitat in the Arctic National Wildlife Refuge, Alaska. Arctic 59(1): 31-36 (March 2006).
Although winters in the arctic present bone-chilling cold, biting winds, and long nights, this is an important time for developing polar bear cubs. The cubs are born in mid-winter—tiny, hairless and helpless. They are protected within dens of ice and snow that provide relative warmth and stable temperatures.
In arctic Alaska, winter snows are generally only 4 to 16 inches deep, so female polar bears dig their dens in the deep autumn snow drifts that collect in localized patches along coastal bluffs, river banks, and steep lakeshores. Among the Beaufort Sea population of polar bears, approximately 50% of the pregnant females come ashore each autumn to construct dens in these snowdrifts, while the other pregnant females dig their dens into snowdrifts on the sea ice.
The map above shows the locations of potential polar bear denning habitat within the Arctic Refuge coastal plain. These locations were identified from high-resolution landscape photographs of the area, and were ground-checked to ensure that they were correctly selected.
This map identifies 3621 km of potential den habitat along the edges of offshore islands and coastal banks, river and stream banks, and lakeshores. The average width of actual denning areas is 6.4 meters, so, based on this width, the total area of den habitat within the Refuge study area is 23.2 km2, or 0.29% of the total 7994 km2 study area.
Based on this work, researchers discovered that the coastal plain of the Arctic Refuge has 38% more den habitat than does Alaska’s central coastal plain immediately west of the Refuge, where denning habitat covers only 11.4 km2, or 0.18% within that 6335.4 km2 study area. Denning habitat is also more uniformly distributed within the Arctic Refuge than it is further west. Although den habitat represents only a small proportion of the Arctic Refuge coastal plain, its wide distribution makes it an important landscape feature.
These factors may explain why a greater than expected number of on-land dens discovered in Alaska between 1981 and 2005 were on the coastal plain of the Arctic Refuge. More bears may use the area of the Refuge because it has more den habitat.
September 12, 2008