Pregnant polar bears enter maternity dens in October/November, give birth to cubs in December/January, and exit dens in March/April. Historically, most polar bears from the Southern Beaufort Sea (SBS) population constructed maternity dens on the sea ice. Over the last three decades, as sea ice has become thinner and prone to fragmentation, there has been a landward shift in the distribution of dens. Based on data from radio-tagged adult female bears in the SBS, maternal denning now occurs at relatively high densities along the Arctic coastal plain of Alaska. The availability of denning habitat―mediated by landscape features that facilitate the formation of snow drifts―appears to increase in the eastern portion of the Alaska coastal plain. In the Chukchi Sea, polar bears historically denned mostly on land in both Russia and the Alaska. Recently, Chukchi Sea polar bears have shifted land-based denning northward on Islands in Russia and rarely on the Alaskan coast. Identifying factors influencing the distribution and duration of dens will allow us to better monitor reproductive success and mitigate the potential for disturbance of denned bears from
Return to Ecosystems >> Marine Ecosystems >> Polar Bear Research
Mapping terrestrial maternal denning habitat
Denning is one of the most vulnerable times in polar bear life history as the family group cannot simply walk away from a disturbance without jeopardizing survival of newly born cubs. Because future industrial activities could overlap habitats used by denning polar bears, identifying these habitats can inform the decisions of resource managers tasked to develop resources and protect polar bears. To help inform these efforts, we are investigating methods for improving the detection and mapping of maternal denning habitat. Recently, we have investigated the efficacy of using interferometric synthetic aperture radar (IfSAR) and light detection and ranging (LiDAR) digital terrain models (DTM) to identify putative denning habitat on portions of Alaska’s coastal plain. This work provides a foundation for developing improved models of terrestrial denning habitat for the entire coastal plain region.
Denning phenology and reproductive success
Female polar bears must accumulate sufficient energy reserves prior to entering dens to produce and nurse cubs before exiting dens in spring. Adequate time spent in a den is important to optimize cub development for withstanding harsh Arctic spring conditions. A recent examination of relationships between den phenology (i.e., timing of den entry and exit), reproductive success, and environmental factors showed that females observed with cubs emerged from dens later and remained in dens approximately two weeks longer than females that emerged from dens but were seen without cubs. Females occupying land-based dens, where estimated snowfall was greater, had higher reproductive success. During years with a greater area of autumn sea ice, reproductive success was higher at land-based versus sea-ice dens, suggesting continued decline in sea ice could negatively affect recruitment. Future work will delve into better understanding mechanistic relationships between denning phenology, environmental conditions, and reproductive success. Because females emerging later from dens had higher reproductive success, den duration could be a useful metric in population monitoring.
Maternal den catalog and database
We maintain a catalog and database on the approximate locations and methods of discovery of polar bear maternal dens found in the Beaufort Sea and neighboring regions since 1910. The catalog includes a description of data collection methods, biases associated with collection method, primary time periods, and spatial resolution of the approximate den location. Data (updated periodically) on past polar bear maternal den locations are provided to inform the public and to provide information for natural resource agencies and industry in planning activities to avoid or minimize interference with polar bear maternity dens.
Below are other science projects associated with this project.
Polar Bear Research
Polar Bear Population Dynamics
Distribution and Movements of Polar Bears
Health and Energetics of Polar Bears
Below are data or web applications associated with this project.
Denning Phenology, Den Substrate, and Reproductive Success of Female Polar Bears (Ursus maritimus) in the southern Beaufort Sea 1986-2013 and the Chukchi Sea 1987-1994
Below are publications associated with this project.
Modeling the spatial and temporal dynamics of land-based polar bear denning in Alaska
Catalogue of polar bear (Ursus maritimus) maternal den locations in the Beaufort and Chukchi Seas and nearby areas, 1910–2018
Seismic survey design and impacts to maternal polar bear dens
A comparison of photograph-interpreted and IfSAR-derived maps of polar bear denning habitat for the 1002 Area of the Arctic National Wildlife Refuge, Alaska
Mapping polar bear maternal denning habitat in the National Petroleum Reserve -- Alaska with an IfSAR digital terrain model
Catalogue of polar bear (Ursus maritimus) maternal den locations in the Beaufort Sea and neighboring regions, Alaska, 1910–2010
Post-den emergence behavior of polar bears (Ursus maritimus) in Northern Alaska
Polar bear maternal den habitat in the Arctic National Wildlife Refuge, Alaska
Detecting denning polar bears with Forward-Looking Infrared (FLIR) imagery
- Overview
Pregnant polar bears enter maternity dens in October/November, give birth to cubs in December/January, and exit dens in March/April. Historically, most polar bears from the Southern Beaufort Sea (SBS) population constructed maternity dens on the sea ice. Over the last three decades, as sea ice has become thinner and prone to fragmentation, there has been a landward shift in the distribution of dens. Based on data from radio-tagged adult female bears in the SBS, maternal denning now occurs at relatively high densities along the Arctic coastal plain of Alaska. The availability of denning habitat―mediated by landscape features that facilitate the formation of snow drifts―appears to increase in the eastern portion of the Alaska coastal plain. In the Chukchi Sea, polar bears historically denned mostly on land in both Russia and the Alaska. Recently, Chukchi Sea polar bears have shifted land-based denning northward on Islands in Russia and rarely on the Alaskan coast. Identifying factors influencing the distribution and duration of dens will allow us to better monitor reproductive success and mitigate the potential for disturbance of denned bears from
Return to Ecosystems >> Marine Ecosystems >> Polar Bear Research
A view from the inside of a polar bear den in the Chukchi Sea, Alaska. (Public domain.) Mapping terrestrial maternal denning habitat
Denning is one of the most vulnerable times in polar bear life history as the family group cannot simply walk away from a disturbance without jeopardizing survival of newly born cubs. Because future industrial activities could overlap habitats used by denning polar bears, identifying these habitats can inform the decisions of resource managers tasked to develop resources and protect polar bears. To help inform these efforts, we are investigating methods for improving the detection and mapping of maternal denning habitat. Recently, we have investigated the efficacy of using interferometric synthetic aperture radar (IfSAR) and light detection and ranging (LiDAR) digital terrain models (DTM) to identify putative denning habitat on portions of Alaska’s coastal plain. This work provides a foundation for developing improved models of terrestrial denning habitat for the entire coastal plain region.
Denning phenology and reproductive success
Female polar bears must accumulate sufficient energy reserves prior to entering dens to produce and nurse cubs before exiting dens in spring. Adequate time spent in a den is important to optimize cub development for withstanding harsh Arctic spring conditions. A recent examination of relationships between den phenology (i.e., timing of den entry and exit), reproductive success, and environmental factors showed that females observed with cubs emerged from dens later and remained in dens approximately two weeks longer than females that emerged from dens but were seen without cubs. Females occupying land-based dens, where estimated snowfall was greater, had higher reproductive success. During years with a greater area of autumn sea ice, reproductive success was higher at land-based versus sea-ice dens, suggesting continued decline in sea ice could negatively affect recruitment. Future work will delve into better understanding mechanistic relationships between denning phenology, environmental conditions, and reproductive success. Because females emerging later from dens had higher reproductive success, den duration could be a useful metric in population monitoring.
Maternal den catalog and database
We maintain a catalog and database on the approximate locations and methods of discovery of polar bear maternal dens found in the Beaufort Sea and neighboring regions since 1910. The catalog includes a description of data collection methods, biases associated with collection method, primary time periods, and spatial resolution of the approximate den location. Data (updated periodically) on past polar bear maternal den locations are provided to inform the public and to provide information for natural resource agencies and industry in planning activities to avoid or minimize interference with polar bear maternity dens.
- Science
Below are other science projects associated with this project.
Polar Bear Research
Polar bears (Ursus maritimus) are one of 4 marine mammal species managed by the U.S. Department of Interior. The USGS Alaska Science Center leads long–term research on polar bears to inform local, state, national and international policy makers regarding conservation of the species and its habitat. Our studies, ongoing since 1985, are focused on population dynamics, health and energetics...Polar Bear Population Dynamics
Information on the status and trends of polar bear populations are needed to inform management of polar bears under US laws and international agreements. The USGS maintains a long-term research program focused on the population dynamics of the southern Beaufort Sea polar bear population. In addition, the USGS collaborates with the US Fish and Wildlife Service in population studies in the Chukchi...Distribution and Movements of Polar Bears
Polar bears are tied to the sea ice for nearly all of their life cycle functions. Most important of these is foraging, or access to food. Polar bears almost exclusively eat seals, and they are equally as dependent upon the sea for their nutrition as are seals, whales, and other aquatic mammals. Polar bears are not aquatic, however, and their only access to the seals is from the surface of the sea...Health and Energetics of Polar Bears
Research in this focal area is centered on (i) collecting data on a variety of systems that help determine and mediate polar bear health and energetics, and (ii) developing monitoring and surveillance programs for detecting changes in population health over time. Additionally, this work will allow us to develop an understanding of how polar bear populations will respond to a variety of stressors... - Data
Below are data or web applications associated with this project.
Denning Phenology, Den Substrate, and Reproductive Success of Female Polar Bears (Ursus maritimus) in the southern Beaufort Sea 1986-2013 and the Chukchi Sea 1987-1994
These data represent estimates of den entrance and exit dates for female polar bears in the southern Beaufort and Chukchi Seas based on temperature sensor data obtained from satellite collars. An algorithm described in Olson et al. (2017) was used to determine whether the female entered a den and further analyses using temperature data as described in Olson et al. (2017) were used to assess den en - Publications
Below are publications associated with this project.
Modeling the spatial and temporal dynamics of land-based polar bear denning in Alaska
Although polar bears (Ursus maritimus) of the Southern Beaufort Sea (SBS) subpopulation have commonly created maternal dens on sea ice in the past, maternal dens on land have become increasingly prevalent as sea ice declines. This trend creates conditions for increased human–bear interactions associated with local communities and industrial activity. Maternal denning is a vulnerable period in theCatalogue of polar bear (Ursus maritimus) maternal den locations in the Beaufort and Chukchi Seas and nearby areas, 1910–2018
This report presents data on the approximate locations and methods of discovery of 530 polar bear (Ursus maritimus) maternal dens observed in the Beaufort and Chukchi Seas and neighboring areas from 1910 to 2018, and archived partly by the U.S. Geological Survey, Alaska Science Center, and partly by the U.S. Fish and Wildlife Service, Marine Mammals Management, in Anchorage, Alaska. A descriptionSeismic survey design and impacts to maternal polar bear dens
Large‐scale industrial activities can have negative effects on wildlife populations. Some of these effects, however, could be reduced with effective planning prior to development. The Coastal Plain of the Arctic National Wildlife Refuge, in northeastern Alaska, USA, is an important maternal denning area for polar bears (Ursus maritimus). Recent legislation has opened the area for potential oil andA comparison of photograph-interpreted and IfSAR-derived maps of polar bear denning habitat for the 1002 Area of the Arctic National Wildlife Refuge, Alaska
Polar bears (Ursus maritimus) in Alaska use the Arctic National Wildlife Refuge (ANWR) for maternal denning. Pregnant bears den in snow banks for more than 3 months in winter during which they give birth to and nurture young. Denning is one of the most vulnerable times in polar bear life history as the family group cannot simply walk away from a disturbance without jeopardizing survival of newly bMapping polar bear maternal denning habitat in the National Petroleum Reserve -- Alaska with an IfSAR digital terrain model
The National Petroleum Reserve–Alaska (NPR-A) in northeastern Alaska provides winter maternal denning habitat for polar bears (Ursus maritimus) and also has high potential for recoverable hydrocarbons. Denning polar bears exposed to human activities may abandon their dens before their young are able to survive the severity of Arctic winter weather. To ensure that wintertime petroleum activities doCatalogue of polar bear (Ursus maritimus) maternal den locations in the Beaufort Sea and neighboring regions, Alaska, 1910–2010
This report presents data on the approximate locations and methods of discovery of 392 polar bear (Ursus maritimus) maternal dens found in the Beaufort Sea and neighboring regions between 1910 and 2010 that are archived by the U.S. Geological Survey, Alaska Science Center, Anchorage, Alaska. A description of data collection methods, biases associated with collection method, primary time periods, aPost-den emergence behavior of polar bears (Ursus maritimus) in Northern Alaska
We observed polar bear (Ursus maritimus) maternity den sites on Alaska’s North Slope in March 2002 and 2003 in an effort to describe bears’ post-den emergence behavior. During 40 sessions spanning 459 h, we observed 8 adults and 14 dependent cubs outside dens for 37.5 h (8.2% of total observation time). There was no significant difference between den emergence dates in 2002 (mean = 15 Mar ± 4.1 d)Polar bear maternal den habitat in the Arctic National Wildlife Refuge, Alaska
Polar bears (Ursus maritimus) give birth during mid-winter in dens of ice and snow. Denning polar bears subjected to human disturbances may abandon dens before their altricial young can survive the rigors of the Arctic winter. Because the Arctic coastal plain of Alaska is an area of high petroleum potential and contains existing and planned oil field developments, the distribution of polar bear deDetecting denning polar bears with Forward-Looking Infrared (FLIR) imagery
Polar bears give birth in snow dens in midwinter and remain in dens until early spring. The survival and development of cubs is dependent on a stable environment within the maternal den. To mitigate potential disruption of polar bear denning by existing and proposed petroleum activities, we used forward-looking infrared (FLIR) viewing to try to detect heat rising from dens.We flew transects over d