THIS POST IS A CRITICAL COMMENTARY ON THE CLIMATE SCIENCE ASSUMPTION IN POLAR BEAR RESEARCH THAT OBSERVED CHANGES IN POLAR BEAR COUNTS AND PHYSICAL CONDITIONS OVER DECADAL TIME SCALES CAN BE UNDERSTOOD IN TERMS OF REDUCED SEA ICE EXTENT AND THEREFORE IN TERMS OF CLIMATE CHANGE WITH THE IMPLICATION THAT WE CAN SAVE POLAR BEARS BY TAKING CLIMATE ACTION.

SUMMARY: Whether the polar bears are in trouble is not the issue. The only issue is whether their trouble if any is caused by fossil fuel emissions and whether it can be moderated by taking climate action. This important aspect of the polar bear issue in climate science is missing from polar bear research carried out by climate science because these relationships are assumed into the research question and methodology as well as in the interpretation of results. Such research is not carried out to seek the relevant information but rather to provide the needed motivation for climate action in a campaign against fossil fuels. The research methods impose confirmation bias into the findings such that they have no interpretation or context outside of the climate change assumptions built into the research methodology.

Life on earth is a struggle for survival for all species in an evolutionary dynamic of specie extinctions and creations. It is not something that needs to be fixed by humans and not something that can be fixed by giving up fossil fuels.

PART-1: THE VIEW FROM CLIMATE SCIENCE AND THE MEDIA

1. Fasting season length sets temporal limits for global polar bear persistence. Péter K. Molnár ETAL, Nature Climate Change volume 10, (2020): Abstract: Polar bears require sea ice for capturing seals and are expected to decline range-wide as global warming and sea-ice loss continue. Estimating when different subpopulations will likely begin to decline has not been possible to date because data linking ice availability to demographic performance are unavailable for most subpopulations and unobtainable a priori for the projected but yet-to-be-observed low ice extremes. Here, we establish the likely nature, timing and order of future demographic impacts by estimating the threshold numbers of days that polar bears can fast before cub recruitment and/or adult survival are impacted and decline rapidly. Intersecting these fasting impact thresholds with projected numbers of ice-free days, estimated from a large ensemble of an Earth system models, reveals when demographic impacts will likely occur in different subpopulations across the Arctic. Our model captures demographic trends observed during 1979–2016, showing that recruitment and survival impact thresholds may already have been exceeded in some subpopulations. It also suggests that, with high greenhouse gas emissions, steeply declining reproduction and survival will jeopardize the persistence of all but a few high-Arctic subpopulations by 2100. Moderate emissions mitigation prolongs persistence but is unlikely to prevent some subpopulation extirpations within this century.
2. NEW YORK TIMES: https://www.nytimes.com/2020/07/20/climate/polar-bear-extinction.html July 20, 2020: CITING THE MOLNAR PAPER: Polar bears could become nearly extinct by the end of the century as a result of shrinking sea ice in the Arctic if global warming continues unabated. Nearly all of the 19 subpopulations of polar bears, from the Beaufort Sea off Alaska to the Siberian Arctic, would face being wiped out because the loss of sea ice would force the animals onto land and away from their food supplies for longer periods. Prolonged fasting, and reduced nursing of cubs by mothers, would lead to rapid declines in reproduction and survival.
3. There are about 25,000 polar bears in the Arctic. Their main habitat is sea ice, where they hunt seals by waiting for them to surface at holes in the ice. In some areas the bears remain on the ice year round, but in others the melting in spring and summer forces them to come ashore. They need the sea ice to capture their food. There’s not enough food on land to sustain a polar bear population. But bears can fast for months, (8 months). Arctic sea ice grows in the winter and melts and retreats in spring and summer. As the region has warmed rapidly in recent decades, sea ice extent in summer has declined by about 13 percent per decade compared to the 1981-2010 average. Some parts of the Arctic that previously had ice year-round now have ice-free periods in summer. Other parts are now free of ice for a longer portion of the year than in the past. The Molnar paper studied 13 of the subpopulations equal to 80 percent of the total bear population. They calculated the bears’ energy requirements in order to determine how long they could survive or, in the case of females, survive and nurse their cubs while fasting. Combining that with climate-model projections of ice-free days to 2100 they found that, for almost all of the subpopulations, the time that the animals would be forced to fast would eventually exceed the time that they are capable of fasting. The animals would starve. Longer fasting time also means a shorter feeding period. Not only do the bears have to fast for longer and need more energy to get through this, they also have a harder time to accumulate this energy. While fasting, bears move as little as possible to conserve energy. But sea-ice loss and population declines require having to expend more energy searching for a mate and that also affects survival. Even under more modest warming projections, in which greenhouse gas emissions peak by 2040 and then begin to decline, many of the subgroups would still be wiped out. Over the years, polar bears have become a symbol both for those who argue that urgent action on global warming is needed and for those who claim that climate change is not happening or, at best, that the issue is overblown. Groups including the Cato Institute, a libertarian research organization that challenges aspects of climate change, have called concerns about the bears unwarranted, arguing that some research shows that the animals have survived repeated warm periods. But scientists say during earlier warm periods the bears probably had significant alternative food sources, notably whales, that they do not have today. Poignant images of bears on isolated ice floes or roaming land in search of food have been used by conservation groups and others to showcase the need for action to reduce warming. Occasionally, though, these images have been shown to be not what they seem. After a video of an emaciated bear picking through garbage cans in the Canadian Arctic was posted online by National Geographic in 2017, the magazine acknowledged that the bear’s condition might not be related to climate change. Scientists had pointed out that there was no way of knowing what was wrong with the bear; it might have been sick or very old. The new research did not include projections in which emissions were reduced drastically, said Cecilia M. Bitz, an atmospheric scientist at the University of Washington and an author of the study. The research needs to be able to determine the periods when sea ice would be gone from a particular region. Andrew Derocher, a polar bear researcher at the University of Alberta said the findings “are very consistent with what we’re seeing” from, for instance, monitoring the animals in the wild. “The study shows clearly that polar bears are going to do better with less warming,” he added. “But no matter which scenario you look at, there are serious concerns about conservation of the species. Of the 19 subpopulations, little is known about some of them, particularly those in the Russian Arctic. Of subpopulations that have been studied, some generally sub-populations in areas with less ice loss have shown little population decline so far. But others, notably in the southern Beaufort Sea off northeastern Alaska, and in the western Hudson Bay in Canada, have been severely affected by loss of sea ice. One analysis found that the Southern Beaufort Sea subpopulation declined by 40 percent, to about 900 bears, in the first decade of this century (2000-2010) . Derocher said one drawback with studies like these is that, while they can show the long-term trends, it becomes very difficult to model what is happening from year to year. Polar bear populations can be very susceptible to drastic year-to-year changes in conditions, he said. “One of the big conservation challenges is that one or two bad years can take down a sub-population that is healthy and push it to really low levels.

CRITICAL COMMENTARY

BIAS IN THE RESEARCH QUESTION AND METHODOLOGY INCLUDES AN EXCLUSIVE FOCUS ON SEA ICE EXTENT AS THE ONLY DETERMINANT OF POLAR BEAR SUB-POPULATION DYNAMICS: As seen in the variables listed below that are known to affect polar bear subpopulation dynamics, it is a gross over-simplification to interpret these dynamics purely in terms of summer minimum sea ice extent. Human predation of polar bears in terms of hunting for food and hide has been a feature of polar bear subpopulation dynamics (PBSPD) for thousands of years. Its intensity increased sharply 500 years ago when commercial bear hide trade boomed and again 70 years ago when snowmobiles, speed boats, and aircraft were employed in the post war explosion of the bear hide business. It is widely believed that polar bear hunting has now been banned but this is not true outside of Norway and some regions of Siberia where some restrictions have been placed on polar bear hunting. Native Arctic humans that have always hunted polar bears for food, clothing, and other purposes have no restrictions. However, polar bear hunting by outsiders is restricted by an international agreement that forbids the use of snowmobiles, speedboats, and aircraft in these hunts. This agreement does not prohibit hunting of polar bears for hide. Non-human predation: in addition to human predation, we find that young polar bears cubs are hunted by wolves and by adult polar bears for food. Starving nursing mothers may also feast on her cubs. In general Intra-species predation is prevalent among polar bears where strong young males may feast on cubs or weaker females. Also, fighting among males for mating partners or hunting rights may also result in death and cannibalism. Polar bears may look cute and cuddly but they are not as nice as they look. These behaviors of Polar Bears (and bears in general), though well known, is treated as anomalous in climate science research and attributed to AGW climate change by way of sea ice loss. See for example, Amstrup and Stirling 2006 in the bibliography below.

NON-CLIMATE FACTORS IN POLAR BEAR SUB-POPULATION DYNAMICS

LONGEVITY: Generally 20 to 30 years but as low as 15 and as high as 32. You can tell how old it is by looking at a thin slice of tooth and counting the layers. PREDATION: Adult polar bears have no predators except other polar bears but cubs less than one year old sometimes are prey to wolves and other carnivores and newborns may be eaten by the polar bears themselves especially if the mother is starved. INTRA-SPECIES PREDATION: This does not happen a lot but males fight over females and will kill the competition to get the lady he wants. In extreme hunger conditions, male polar bears may attack, kill, and eat female polar bears. This is not a normal behavior pattern but it does happen. HUMAN PREDATION: Humans have hunted, killed, and eaten Polar bears for thousands of years. Arctic people have traditionally hunted polar bears for food, clothing, bedding, and religious purposes. More recently commercial hunting for polar bear hides got started more than 500 years ago. There was a sharp rise in the kill rate in the 1950s when modern equipment such as snowmobiles, speedboats, and aircraft were employed in the polar bear hide trade. The hunt expanded to what was eventually viewed as a threat to the survival of the species and an International Agreement was signed in 1973 to ban the use of aircraft and speed boats in polar bear hunts although hunting continued to the extent that they were still the leading cause of polar bear mortality. It is popularly believed that polar bear hunting is now banned. STATE OF HUMAN PREDATION: Today, polar bears are hunted by native arctic populations for food, clothing, handicrafts, and sale of skins. Polar bears are also killed in defense of people or property. However, hunting is strictly regulated in Canada, Greenland, Norway, and Russia. In Norway and Russia hunting polar bears is banned. CLIMATE CHANGE IMPACT: Increasing temperatures are associated with a decrease in sea ice both in terms of how much sea ice there is and how many months a year they are there. Polar bears use sea ice as a platform to prey mainly on ringed and bearded seals. Therefore, a decline in sea ice extent reduces the polar bear’s ability to hunt for seals and can cause bears to starve or at least to be malnourished. YOUNG POLAR BEARS: Subadults are inexperienced hunters, and often are chased from kills by larger adults. OLD & WEAK BEARS are also susceptible to starvation for the same reason. They can’t compete with younger and stronger bears. In hunt constrained situations, as in limited sea ice, kids and seniors starve first. Climate change scientists have found (bibliography in related post) that polar bear subpopulations have shown increasing evidence of food deprivation including an increase in the number of underweight or starving bears, smaller bears, fewer cubs, and cubs that don’t survive into adulthood partially because in food constrained situations cubs are more likely to be eaten by adult polar bears. This takes place in areas that are experiencing shorter hunting seasons with limited access to sea ice. These conditions limit the bears’ ability to hunt for seals.

The implication for climate impact studies is that a comparison of polar bear subpopulation counts across time at brief decadal time scales, in and of itself, may not have a climate change sea ice interpretation because of the number of other variables involved in these dynamics.

See for example the bibliography below where papers like Bromaghin etal 2015, though they carry out the analysis based on the sea ice climate change as the cause of observed population dynamics, they also admit that there are other drivers of polar bear sub-population dynamics that have not been included in the analysis. Two other characteristics of these studies are that (1) changes at short time scales of 5 years or less are interpreted as trends related to AGW global warming and sea ice decline; and (2) a pattern in research methodology of first identifying some changes at these short time scales and then finding ways to attribute the observed changes to sea ice dynamics and therefore to AGW climate change. (see for example Pagano 2012).

A confirmation bias methodology is the norm. Few papers express that clearly but in papers such as Pongracz and Derocher 2017 the authors admit that their research is motivated and guided by the assumption that “Climate change is altering habitats and causing changes to species behaviors and distributions. Rapid changes in Arctic sea ice ecosystems have increased the need to identify critical habitats for conservation and management of species such as polar bears” and that they therefore examined the distribution of adult female and subadult male and female polar bears and interpreted the terrestrial and sea ice areas used as summer refugia in terms of sea ice melt.

Yet another factor is the assumption that observed changes in September minimum sea ice extent are driven by global warming such that they can be moderated by taking climate action by reducing or eliminating the use of fossil fuels. This critical causal relationship is simply assumed in climate science. However, as shown in related posts: LINK: https://tambonthongchai.com/2020/09/25/list-of-arctic-sea-ice-posts/ , detrended correlation analysis does not show that September minimum Arctic sea ice extent is responsive to air temperature above the Arctic. This means that we have no evidence to support the assumption that fossil fuel emissions cause lower September minimum sea ice extent and that this trend can be attenuated by taking climate action. Thus, in short, the two critical causations in polar bear research by climate scientists, (1) that fossil fuel emissions lower September minimum sea ice extent and (2) that polar bear sub-population dynamics are the creation of changes in September minimum sea ice extent, are simply assumed with no empirical evidence provided to support them.

In this context it should be noted that the Arctic is geologically very active with significant mantle plume activity and ocean floor volcanism as described in a related post: LINK: https://tambonthongchai.com/2019/07/01/arctic/ . It is therefore necessary to take these effects into consideration in the study of ice melt events in the Arctic instead of the extreme effort in climate science to explain all Arctic ice melt phenomena in terms of the atmosphere.

SUMMARY: Whether the polar bears are in trouble is not the issue. The only issue is whether their trouble if any is caused by fossil fuel emissions and whether it can be moderated by taking climate action. This important aspect of the polar bear issue in climate science is missing from polar bear research carried out by climate science apparently to provide the needed motivation for climate action in a campaign against fossil fuels.

RINGED SEALS

THE RELEVANT BIBLIOGRAPHY

1. Regehr, Eric V., et al. “Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice.” Journal of animal ecology 79.1 (2010): 117-127. Observed and predicted declines in Arctic sea ice have raised concerns about marine mammals. In May 2008, the US Fish and Wildlife Service listed polar bears (Ursus maritimus) – one of the most ice‐dependent marine mammals – as threatened under the US Endangered Species Act. We evaluated the effects of sea ice conditions on vital rates (survival and breeding probabilities) for polar bears in the southern Beaufort Sea. Although sea ice declines in this and other regions of the polar basin have been among the greatest in the Arctic, to date population‐level effects of sea ice loss on polar bears have only been identified in western Hudson Bay, near the southern limit of the species’ range. We estimated vital rates using multistate capture–recapture models that classified individuals by sex, age and reproductive category. We used multimodel inference to evaluate a range of statistical models, all of which were structurally based on the polar bear life cycle. We estimated parameters by model averaging, and developed a parametric bootstrap procedure to quantify parameter uncertainty. In the most supported models, polar bear survival declined with an increasing number of days per year that waters over the continental shelf were ice free. In 2001–2003, the ice‐free period was relatively short (mean 101 days) and adult female survival was high (0·96–0·99, depending on reproductive state). In 2004 and 2005, the ice‐free period was longer (mean 135 days) and adult female survival was low (0·73–0·79, depending on reproductive state). Breeding rates and cub litter survival also declined with increasing duration of the ice‐free period. Confidence intervals on vital rate estimates were wide. The effects of sea ice loss on polar bears in the southern Beaufort Sea may apply to polar bear populations in other portions of the polar basin that have similar sea ice dynamics and have experienced similar, or more severe, sea ice declines. Our findings therefore are relevant to the extinction risk facing approximately one‐third of the world’s polar bears.
2. Schliebe, S., et al. “Effects of sea ice extent and food availability on spatial and temporal distribution of polar bears during the fall open-water period in the Southern Beaufort Sea.” Polar Biology 31.8 (2008): 999-1010. We investigated the relationship between sea ice conditions, food availability, and the fall distribution of polar bears in terrestrial habitats of the Southern Beaufort Sea via weekly aerial surveys in 2000–2005. Aerial surveys were conducted weekly during September and October along the Southern Beaufort Sea coastline and barrier islands between Barrow and the Canadian border to determine polar bear density on land. The number of bears on land both within and among years increased when sea-ice was retreated furthest from the shore. However, spatial distribution also appeared to be related to the availability of subsistence-harvested bowhead whale carcasses and the density of ringed seals in offshore waters. Our results suggest that long-term reductions in sea-ice could result in an increasing proportion of the Southern Beaufort Sea polar bear population coming on land during the fall open-water period and an increase in the amount of time individual bears spend on land.
3. Hunter, Christine M., et al. “Polar bears in the Southern Beaufort Sea II: Demography and population growth in relation to sea ice conditions.” USGS Alaska Science Center, Anchorage, Administrative Report (2007). This is a demographic analysis of the southern Beaufort (SB) polar bear population. The analysis uses a female-dominant stage-classified matrix population model in which individuals are classified by age and breeding status. Parameters were estimated from capture-recapture data collected between 2001 and 2006. We focused on measures of long-term population growth rate and on projections of population size over the next 100 years. We obtained these results from both deterministic and stochastic demographic models. Demographic results were related to a measure of sea ice condition, ice(t), defined as the number of ice-free days, in year t, in the region of preferred polar bear habitat. Larger values of ice(t) correspond to lower availability of sea ice and longer ice-free periods. Uncertainty in results was quantified using a parametric bootstrap approach that includes both sampling uncertainty and model selection uncertainty. Deterministic models yielded estimates of population growth rate λ, under low ice conditions in 2001–2003, ranging from 1.02 to 1.08. Under high ice conditions in 2004–2005, estimates of λ ranged from 0.77 to 0.90. The overall growth rate estimated from a time-invariant model was about 0.997; i.e., a 0.3% decline per year. Population growth rate was most elastic to changes in adult female survival, and an LTRE analysis showed that the decline in λ relative to 2001 conditions was primarily due to reduction in adult female survival, with secondary contributions from reduced breeding probability. Based on demographic responses, we classified environmental conditions into good (2001– 2003) and bad (2004–2005) years, and used this classification to construct stochastic models. In those models, good and bad years occur independently with specified probabilities. We found that the stochastic growth rate declines with an increase in the frequency of bad years. The observed frequency of bad years since 1979 would imply a stochastic growth rate of about -1% per year. Deterministic population projections over the next century predict serious declines unless conditions typical of 2001–2003 were somehow to be maintained. Stochastic projections predict a high probability of serious declines unless the frequency of bad ice years is less than its recent average. To explore future trends in sea ice, we used the output of 10 selected general circulation models (GCMs), forced with “business as usual” greenhouse gas emissions, to predict values of ice(t) until the end of the century. We coupled these to the stochastic demographic model to project population trends under scenarios of future climate change. All GCM models predict a crash in the population within the next century, possibly preceded by a transient population increase. The parameter estimates on which the demographic models are based have high levels of uncertainty associated with them, but the agreement of results from different statistical model sets, deterministic and stochastic models, and models with and without climate forcing, speaks for the robustness of the conclusions.
4. Bromaghin, Jeffrey F., et al. “Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline.” Ecological Applications 25.3 (2015): 634-651. In the southern Beaufort Sea of the United States and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears. Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark–recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25–50% decline in abundance. We hypothesize that low survival during this period resulted from (1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly, (2) low prey abundance. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010, with ~900 bears in 2010 (90% CI 606–1212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.
5. Stirling, Ian, et al. “Unusual predation attempts of polar bears on ringed seals in the southern Beaufort Sea: possible significance of changing spring ice conditions.” Arctic (2008): 14-22. In April and May 2003 through 2006, unusually rough and rafted sea ice extended for several tens of kilometres offshore in the southeastern Beaufort Sea from about Atkinson Point to the Alaska border. Hunting success of polar bears seeking seals was low despite extensive searching for prey. It is unknown whether seals were less abundant in comparison to other years or less accessible because they maintained breathing holes below rafted ice rather than snowdrifts, or whether some other factor was involved. However, we found 13 sites where polar bears had clawed holes through rafted ice in attempts to capture ringed seals in 2005 through 2006 and another site during an additional research project in 2007. Ice thickness at the 12 sites that we measured averaged 41 cm. These observations, along with cannibalized and starved polar bears found on the sea ice in the same general area in the springs of 2004 through 2006, suggest that during those years, polar bears in the southern Beaufort Sea were nutritionally stressed. Searches made farther north during the same period and using the same methods produced no similar observations near Banks Island or in Amundsen Gulf. A possible underlying ecological explanation is a decadal-scale downturn in seal populations. But a more likely explanation is major changes in the sea-ice and marine environment resulting from record amounts and duration of open water in the Beaufort and Chukchi seas, possibly influenced by climate warming. Because the underlying causes of observed changes in polar bear body condition and foraging behavior are unknown, further study is warranted. 
6. Pagano, Anthony M., et al. “Long-distance swimming by polar bears (Ursus maritimus) of the southern Beaufort Sea during years of extensive open water.” Canadian Journal of Zoology 90.5 (2012): 663-676. Polar bears depend on sea ice for catching marine mammal prey. Recent sea-ice declines have been linked to reductions in body condition, survival, and population size. Reduced foraging opportunity is hypothesized to be the primary cause of sea-ice-linked declines, but the costs of travel through a deteriorated sea-ice environment also may be a factor. We used movement data from 52 adult female polar bears wearing GPS collars, including some with dependent young, to document long-distance swimming (>50 km) by polar bears in the southern Beaufort and Chukchi seas. During 6 years (2004–2009), we identified 50 long-distance swims by 20 bears. Swim duration and distance ranged from 0.7 to 9.7 days (mean = 3.4 days) and 53.7 to 687.1 km (mean = 154.2 km), respectively. Frequency of swimming appeared to increase over the course of the study. We show that adult female polar bears and their cubs are capable of swimming long distances during periods when extensive areas of open water are present. However, long-distance swimming appears to have higher energetic demands than moving over sea ice. Our observations suggest long-distance swimming is a behavioral response to declining summer sea-ice conditions.
7. Pongracz, Jodie D., and Andrew E. Derocher. “Summer refugia of polar bears (Ursus maritimus) in the southern Beaufort Sea.” Polar Biology 40.4 (2017): 753-763. Climate change is altering habitats and causing changes to species behaviors and distributions. Rapid changes in Arctic sea ice ecosystems have increased the need to identify critical habitats for conservation and management of species such as polar bears. We examined the distribution of adult female and subadult male and female polar bears tracked by satellite telemetry (n = 64 collars) in the southern Beaufort Sea, Canada, to identify summer refugia in 2007–2010. Using utilization distributions, we identified terrestrial and sea ice areas used as summer refugia when nearshore sea ice melted. Habitat use areas varied between months, but interannual variation was not significant. Overall, bears made high use of ice over shallow waters, and bears that remained near terrestrial areas used sea ice (presumably to hunt from) when it was available. The majority of the bears remained on sea ice during summer and used the edge of the pack ice most notably west of Banks Island, Canada. A mean of 27 % (range 22–33 %) of bears used terrestrial areas in Alaska and use was concentrated near the remains of subsistence harvested bowhead whales (Balaena mysticetus). Energetic expenditure is anticipated to increase as bears are required to travel further on a seasonal basis.
8. Amstrup, Steven C., et al. “Recent observations of intraspecific predation and cannibalism among polar bears in the southern Beaufort Sea.” Polar Biology 29.11 (2006): 997. Intraspecies killing has been reported among polar bears, brown bears, and black bears. Although cannibalism is one motivation for such killings, the ecological factors mediating such events are poorly understood. Between 24 January and 10 April 2004, we confirmed three instances of intraspecies predation and cannibalism in the Beaufort Sea. One of these, the first of this type ever reported for polar bears, was a parturient female killed at her maternal den. The predating bear was hunting in a known maternal denning area and apparently discovered the den by scent. A second predation event involved an adult female and cub recently emerged from their den, and the third involved a yearling male. During 24 years of research on polar bears in the southern Beaufort Sea region of northern Alaska and 34 years in northwestern Canada, we have not seen other incidents of polar bears stalking, killing, and eating other polar bears. We hypothesize that nutritional stresses related to the longer ice-free seasons that have occurred in the Beaufort Sea in recent years may have led to the cannibalism incidents we observed in 2004.