The Un-Bear-able Truth

From Pole to Pole, Series 1, Episode 1, depicts the impacts of raising young polar bear cubs on hibernation cycles and, consequently, survival. This video focuses on the maternal efforts taken to ensure the offsprings’ survival. Polar bears reproduce sexually, and the father has nothing to do with the mother or offspring after mating. After successful mating and hibernation underground, the mother polar bear must lure her cubs out of their den for the first time. This journey serves as instructional time for the cubs because they must rapidly become accustomed to the environment. With little resources available to the offspring, the video stresses that the polar bears need to travel in search of food and that the mother’s milk has been the cubs only source of nutrients.

The cost of having young is present before the cubs are born since the mother must identify a mate and find a safe location to den. Due to environmental changes, researchers have witnessed alterations in polar bear behavioral patterns concerning their denning locations. More polar bears are denning on land rather than floating ice, due to a decrease in available ice. This use of land dens is in contrast to just several years prior [1].


During hibernation, mother polar bears must be able to synthesize milk to sustain their cubs. Without food intake, however, this poses challenging energy demands on the mother to produce milk while not succumbing to metabolic deficits. For example, mother polar bears minimize glucose use in order to avoid tissue/protein loss that would otherwise be utilized for glucose synthesis [2]. In addition to lactation demands, the mother bears must also adapt to various environmental pressures. Once they emerge from hibernation in the spring, the warm weather poses a challenge to acquire food. As the sea ice continues to melt, the mother bear has to quickly hunt to feed her cubs.

Mother polar bears are also hibernating for shorter periods of time due to decreased hunting grounds caused by such environmental effects [3]. Interestingly, compounds in the blood trigger hibernation [4]. Research could track the possible evolution of hibernation by comparing the blood composition of bears now and in the future. The identification of a specific Hibernation-induced factor (HIF) could indicate whether polar bear behavior is genetic, which is important for evolution.

Brandon Chen, Dezmon Scott, Diana Dang, Kevin Sun and Michael Tsai

Planet Earth, Episode 1, “From Pole to Pole”, starting at 3:40

  1. Amstrup SC & C Gardner. 1994. Polar bear maternity denning in the Beaufort Sea. The Journal of Wildlife Management, 1-10.
  2. Oftedal, O. 2000. Use of maternal reserves as a lactation strategy in large mammals. Proceedings of the Nutrition Society, 59(1), 99-106.
  3. Robbins CT, Lopez-Alfaro C, Rode KD, Tøien Ø & OL Nelson. 2012. Hibernation and seasonal fasting in bears: the energetic costs and consequences for polar bears. Journal of Mammalogy, 93(6), 1493-1503.
  4. Bruce DS, Darling NK, Seeland KJ, Oeltgen PR,  Nilekani SP & SC Amstrup. 1990. Is the Polar Bear (Ursus maritimus) a hibernator?: Continued studies on opioids and hibernation. Pharmacology Biochemistry and Behavior, 35(3), 705-711.

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