Polar bears are dying primarily because shrinking sea ice is starving them. As Arctic ice breaks up earlier in spring and forms later in fall, polar bears lose access to their main hunting platform for seals, the calorie-dense prey they depend on. The Western Hudson Bay population alone has dropped nearly 50% since 1979, and the pattern is repeating across the Arctic. But starvation from ice loss is only the most visible pressure. Toxic pollutants, disease, and increasing conflict with humans are compounding the problem.
Sea Ice Loss and the Starvation Cycle
Polar bears hunt seals from sea ice. When the ice melts, the bears are forced onto land where they enter a prolonged fast, burning through fat reserves while waiting for ice to return. In western Hudson Bay, the ice-free season has grown by roughly three weeks compared to the early 1980s, and each additional week on land costs a bear significant body weight.
The energy math is brutal. A ringed seal provides tens of thousands of calories in a single kill. Nothing on land comes close to matching that efficiency. While some researchers have found that land-based foods like caribou, snow goose eggs, and berries could theoretically offset caloric deficits if bears stayed relatively still, the reality is more complicated. Most bears haven’t shifted their foraging behavior enough to exploit these resources consistently, and the energy cost of actively pursuing unfamiliar prey on land can erase whatever calories they gain. Subadults and mothers with cubs have been observed eating terrestrial food more often, but adult males, the largest bears with the biggest energy needs, are slower to adapt.
Mothers Running Out of Milk
The starvation cycle hits nursing mothers hardest. As females spend more time fasting on land, their body condition deteriorates and their milk production drops or stops entirely. After about three months on shore, a mother with a newborn cub has only a 53% chance of still producing milk. For mothers with yearlings, that probability falls to 35%.
Even when mothers keep lactating, the quality of their milk plummets. Females with one cub produce milk with 50% less energy after three months on land. For mothers nursing two cubs, milk energy drops by more than 75%. The result is predictable: cubs grow more slowly, and some stop growing altogether between observation periods. On average, fewer than half of all polar bear cubs survive to adulthood, with the most ice-stressed populations seeing even lower rates. This reproductive failure is a major driver of population decline, because it means fewer bears are replacing the ones that die.
Toxic Chemicals Stored in Fat
Polar bears sit at the top of the Arctic food chain, which means industrial pollutants concentrate in their bodies at alarming levels. Chemicals like PCBs, DDT-related compounds, and flame retardants accumulate in seal blubber and magnify as they move up the food web. By the time a polar bear eats a seal, it’s consuming a concentrated dose of everything that seal absorbed over its lifetime.
These contaminants don’t just sit in fat tissue passively. In multiple subpopulations across the Arctic, pollutant levels exceed the thresholds known to cause health problems. The documented effects include disruption of thyroid hormones, sex hormones, and stress hormones, along with weakened immune systems, reduced bone density, and damage to the liver, kidneys, and thyroid gland. Reproductive impairment is particularly concerning: across all 11 subpopulations examined in one circumpolar analysis, contaminant concentrations still exceeded risk thresholds for reproductive harm, immune suppression, and cancer, even though overall pollutant levels have declined somewhat over the past two decades. For bears already stressed by starvation, a compromised immune system or disrupted hormones can be the difference between surviving a bad ice year and not.
Avian Flu Reaches the Arctic
In 2023, a free-ranging polar bear in Alaska was found dead and tested positive for highly pathogenic H5N1 avian influenza. It was the first confirmed case in a wild polar bear, detected in the southern Beaufort Sea subpopulation. Polar bears likely pick up the virus by scavenging infected seabirds or raiding bird nests, though inhaling the virus is also possible.
Three other polar bears found dead on Alaska’s North Slope that same year tested negative for the virus, so there’s no evidence yet of widespread avian flu sweeping through bear populations. But the concern is real. H5N1 has devastated marine mammal colonies elsewhere, killing thousands of seals and sea lions in South America. Polar bears’ increasing reliance on bird eggs and carcasses as a land-based food source could raise their exposure risk over time, especially as the virus continues circulating in Arctic bird colonies.
More Bears Near More People
As sea ice retreats, hungry bears spend more time on land and increasingly wander into human settlements searching for food. This creates dangerous encounters that frequently end with the bear being killed. Between 2020 and 2024, an average of 70 polar bears per year were killed due to conflicts with humans across the five polar bear range states (Canada, the United States, Norway, Greenland, and Russia).
Canada accounts for the majority of these deaths, with 41 to 67 bears killed annually during this period. The United States, primarily Alaska, has seen its numbers climb from 8 conflict kills in 2020 to 19 in 2023. Bears can be legally killed in defense of human life in Norway, the United States, and Russia, while Canada and Greenland also allow killing in defense of property. Because subsistence hunting by Indigenous communities is legal in Canada, Greenland, and the United States, conflict kills aren’t always tracked separately from harvest numbers, meaning the true toll may be higher than reported.
These numbers might seem small relative to a global population estimated at around 26,000 bears. But polar bears reproduce slowly, typically producing just two cubs every three years, and with cub survival already declining, even modest additional mortality from conflict puts extra pressure on vulnerable subpopulations.
How These Threats Compound
No single factor is killing polar bears in isolation. The threats reinforce each other in ways that make each one worse. A bear that’s already nutritionally stressed from a shortened hunting season mobilizes its fat reserves during fasting, which releases stored pollutants into its bloodstream at higher concentrations. Those pollutants suppress its immune system, making it more vulnerable to diseases like avian influenza. If the bear is a nursing mother, poor body condition reduces her milk output, lowering her cubs’ chances of survival. And if she wanders into a coastal village looking for food scraps, she risks being shot.
The Western Hudson Bay population illustrates this compounding effect clearly. Its roughly 50% decline since 1979 wasn’t caused by a single catastrophic event. It was driven by a steady, decades-long erosion of the conditions bears need to feed, reproduce, and survive, with each additional stressor narrowing the margin further. Other subpopulations across the Arctic face similar trajectories as ice loss accelerates, though the timeline varies by region. Populations in the High Arctic still have relatively stable ice conditions, while those at lower latitudes are already deep into decline.