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Polar Bears Milk Production Affected by Climate Change, Finds Study

Polar Bears laying in snow. Mother Polar Bear cuddling two cubs.

A new study published in conjunction with the University of Toronto finds that dwindling sea ice may have a significant impact on nursing mother Polar Bears’ ability to produce adequate supplies of milk for their cubs. The study looked at Polar Bears from the western Hudson Bay in Canada. In this area, sea ice exists only seasonally.

As sea ice fragments and recedes earlier each year, the time that Polar Bears must spend on land without access to food increases. While forced onto land, Polar Bears do not have as many opportunities to hunt seals. Seals make up the majority of the bears’ diets and are an important source of nutrition for these large mammals. Without regular food, Polar Bears enter a fasting state. In this state, the bears burn their body fat for energy. However, for nursing Polar Bear mothers, longer stays on land mean a difficult decision. The mother bears need to expend immense energy reserves to produce the rich milk on which their cubs depend. When mother bears are nursing during fasting periods they may not be able to continue producing enough milk for their cubs without risking their health.

The recently published study found that longer stays on land affect the nutritional content of mother bears’ milk. Indeed, sometimes the Polar Bears stopped producing milk altogether. Although this protects the health of the mother bear by reducing energy expenditure, the Polar Bear cubs were negatively affected by the reduced nutritional content. Researchers found that the cubs grew at a slower rate. This could have negative effects on the ability of these cubs to survive over time.

Due to sea ice loss, the population of Polar Bears in the western Hudson Bay are now forced to spend roughly four months on land. However, researchers found the probability of a female Polar Bear with cubs producing milk after three months on land was only 53 percent. This percentage dropped to 35 percent if the cubs were yearlings, or cubs born the previous year. Researchers fear that these numbers are even worse than indicated by the data. This is because the data set was collected over 30 years ago. The researchers believe that the effects are likely even more significant than represented by the data set.

The increasing period of the year without sea ice has led to a decline in the condition of many Polar Bear populations. The average Polar Bear’s body size has declined. The population of Polar Bears in the western Hudson Bay has dropped by a staggering 50 percent. Scientists warn that without mitigation strategies, this trend is likely to continue. Indeed, Polar Bear populations throughout the Arctic will be threatened by climate change and sea ice loss.

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