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ABSTRACT. 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 [...]

Observed declines in the Arctic sea ice have resulted in a variety of negative effects on polar bears (Ursus maritimus). Projections for additional future declines in sea ice resulted in [...]

Projections of polar bear (Ursus maritimus) sea ice habitat distribution in the polar basin during the 21st century were developed to understand the consequences of anticipated sea ice reductions on polar bear populations. We used location data from satellite-collared polar bears and environmental data (e.g., bathymetry, distance to coastlines, and sea ice) collected from 1985 to 1995 to build resource selection functions (RSFs). RSFs described habitats that polar bears preferred in summer, autumn, winter, and spring. When applied to independent data from 1996 to 2006, the RSFs consistently identified habitats most frequently used by polar bears. We applied the RSFs to monthly maps of 21st-century sea ice concentration projected by 10 general circulation models (GCMs) used in the Intergovernmental Panel of Climate Change Fourth Assessment Report, under the A1B greenhouse gas forcing scenario. Despite variation in their projections, all GCMs indicated habitat losses in the polar basin during the 21st century. Losses in the highest-valued RSF habitat (optimal habitat) were greatest in the southern seas of the polar basin, especially the Chukchi and Barents seas, and least along the Arctic Ocean shores of Banks Island to northern Greenland. Mean loss of optimal polar bear habitat was greatest during summer; from an observed 1.0 million [km.sup.2] in 1985-1995 (baseline) to a projected multi-model mean of 0.32 million [km.sup.2] in 2090-2099 (-68% change). Projected winter losses of polar bear habitat were less: from 1.7 million [km.sup.2] in 1985 1995 to 1.4 million [km.sup.2] in 2090-2099 (-17% change). Habitat losses based on GCM multi-model means may be conservative; simulated rates of habitat loss during 1985-2006 from many GCMs were less than the actual observed rates of loss. Although a reduction in the total amount of optimal habitat will likely reduce polar bear populations, exact relationships between habitat losses and population demographics remain unknown. Density and energetic effects may become important as polar bears make long-distance annual migrations from traditional winter ranges to remnant high-latitude summer sea ice. These impacts will likely affect specific sex and age groups differently and may ultimately preclude bears from seasonally returning to their traditional ranges. Key words: climate change; general circulation model; IPCC; passive microwave; polar basin; polar bear; radio telemetry; resource selection function; sea ice; SMMR; SSM/I; Ursus maritimus.

ABSTRACT. 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 [...]

ABSTRACT. 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 [...]

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 [...]

Around the world, a great deal of effort is expended each year to estimate the sizes of wild animal populations. Unfortunately, population size has proven to be one of the [...]

ABSTRACT. Polar bears (Ursus maritimus) give birth to and nurture their young in dens of ice and snow. During 1999-2001, we measured the structure of 22 dens on the coastal [...]

Recent research has investigated the suitability of reported models to forecast mass of polar bears captured in northern Alaska. Poor results prompted researchers to develop new models from field measurements of axillary girth, straight-line body length, condylobasal length and zygomatic width. Axillary girth was found to be the most useful predictor of body mass in large ungulates, as indicated in earlier research. However, discrepancies can arise from geographical differences among populations, age and sex.

The temporal and spatial distribution of polar bear (Ursus maritimus) maternal denning in the Beaufort Sea region of Alaska and Canada was studied to improve the understanding of the effects of hunting and industrial development on polar bears. The study protocol involved capturing and attaching radio-collars on bears from 1981-91. The results showed that of 90 dens found, 48 were on pack ice, 38 were on land and four were on land-fast ice. Predictable denning chronology and lack of denning site fidelity may mitigate the effects of human activities on polar bear reprodduction.

Various methods are employed using a satellite radiotelemetry system to locate and estimate the movements of the harvested polar bear population. These techniques are regarded highly valuable to researchers in obtaining perfect descriptions of wildlife populations being scrutinized.

Cases where the Jolly-Seber estimator of population size biased under tag loss and tag-induced mortality were identified by examining the mathematical arguments and performing computer simulations. It was found that, except under certain tag-loss models ad high-sample sizes, the population size estimators are severely biased high when tag loss or tag-induced mortality could have serious consequences for field biologists in interested in population sizes.

GEORGE M. DURNER [1] STEVEN C. AMSTRUP [1] KEN J. AMBROSIUS [2] (Received 1 February 2000; accepted in revised form 30 August 2000) ABSTRACT. Polar bears (Ursus maritimus) give birth [...]