A sweet surprise: Polar bear glucose reveals new insights into their reproduction and conservation

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Polar bears are metabolic marvels, sustained by a lifestyle of eating fat-rich seals that puts even the keto diet to shame. Each year, bears cycle through periods of intense feasting and prolonged fasting, packing on most of their weight in spring. For reproductive females, seasonal bulking is crucial – it fuels the winter denning and fasting period when they give birth.

Females emerge in spring with their cubs, giving biologists a prime chance to assess the population and count new recruits. Yet, a challenge remains: when a lone adult female is observed, does it mean she denned and lost her cubs, or never denned at all? How can reproductive failure in polar bears be detected? Solving problems like these is key to guiding conservation efforts to protect polar bears.

Four polar bears pictured on a snowy landscape.
Karyn Rode (USGS)
An adult female polar bear with three yearlings.

A familiar tool may hold a clue: A1c, a marker of average blood sugar over the past few months. While most people know A1c as a test to monitor diabetes, a team of research biologists saw potential beyond the doctor’s office. A new study published in the Journal of Mammalogy on June 28 explores whether A1c could reveal if a polar bear had recently denned, which – combined with the absence of cubs – may signal reproductive failure.

The study found that polar bears that recently denned had higher A1c levels than those that had not. Why? Fasting polar bears develop insulin resistance – an adaptation that helps maintain blood sugar levels during extended periods without food. While insulin resistance is a hallmark of type 2 diabetes in humans, in bears, it’s an important physiological response to fasting. Pregnancy adds to this effect, resulting in higher blood sugar in pregnant and perinatal females.

Two polar bear cubs with their mother on a snowy landscape.
Mike Lockhart, USGS
Mom and pups: Two young-of-the-year polar bear cubs with their mother on the sea ice.

Thanks to its long-term signature, A1c could be a useful tool for field biologists to detect denning and reproductive events. Monitoring polar bear health is more crucial now than ever, in the face of climate change. Efforts like these can make a real difference in conserving polar bears and the Arctic ecosystem they depend on.

This research was led by University of Washington SAFS doctoral student Sarah Teman in Dr. Kristin Laidre’s lab, in collaboration with scientists from the Cincinnati Zoo Center for Conservation & Research of Endangered Wildlife (CREW) and the U.S. Geological Survey (USGS).

To measure A1c, the team analyzed blood samples from wild polar bears in Alaska’s Southern Beaufort Sea, collected during USGS-led population health assessments. A1c is rarely measured in wildlife, so Teman and Dr. Laidre partnered with CREW’s polar bear reproduction experts, led by Dr. Erin Curry, to develop a workable approach. The solution: adapt and validate a test originally designed for dogs and cats to reliably function for polar bears.

“Creative, collaborative science is where cool ideas turn into actual tools to protect wildlife,” Teman said.

A zoomed out photo of three polar bears on a snowy landscape.
Kristin Laidre
Three polar bears—an adult female with two yearlings—wander across an Arctic landscape.

The next phase of this research will track A1c levels in the same polar bears throughout the year to better understand seasonal fluctuations – particularly in the weeks leading up to and following denning. The team received a Research and Conservation Grant award from the International Association for Bear Research and Management to continue this work using zoo-housed polar bears.

This project was funded by the National Science Foundation Graduate Research Fellowship Program, the Institute of Museum and Library Services, and the USGS Ecosystems Mission Area.

For inquiries, contact Sarah Teman at steman@uw.edu

Citation: Sarah J Teman, Todd C Atwood, Kristin L Laidre, Emily E Virgin, Karyn D Rode, Louisa A Rispoli, Erin Curry, Hemoglobin A1c is a retrospective indicator of denning in polar bears (Ursus maritimus), Journal of Mammalogy, 2025;, gyaf033, https://doi.org/10.1093/jmammal/gyaf033

Scientists pilot a new method to measure the health of wild polar bears

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Climate change threatens the health of polar bears across the Arctic. A study published in Conservation Physiology on March 5, introduces a new approach to measuring the health of polar bear populations, drawing inspiration from a well-known concept in human medicine: allostatic load.

Allostatic load refers to the “wear and tear” on the body that results from chronic stress. In humans, high allostatic load increases the risk for disease and death. A team of scientists used allostatic load principles to create a health scoring model for polar bears in Alaska and Canada’s Southern Beaufort Sea, where the population has declined by 25-50%. The model included measures of nutritional, immune, and chronic stress—factors that are all highly relevant, given the threats facing polar bears. This project was carried out by biologists from the University of Washington School of Aquatic and Fishery Sciences (UW SAFS), United States Geological Survey (USGS), and Fish and Wildlife Health Consulting.

Two polar bears - one adult and one cub - walk on land next to the water's edge. In the background, an old and rusty ship/barge is in the water.
USGS
Two polar bears, an adult female and her cub, on land at Kaktovik, Alaska.

Polar bears depend on sea ice as a hunting platform, and ice loss can lead to poorer nutritional condition. In summer and fall, when the ice retreats northward, bears in the Southern Beaufort Sea must choose between following the ice into less productive hunting areas or moving onto land until the ice refreezes. Increasingly, bears are coming ashore and scavenging human-provisioned foods—an option that may expose them to new pathogens and increase disease risk. Additionally, coming ashore heightens bears’ exposure to human disturbance in areas of expanding oil and gas development, potentially adding further stress to an already vulnerable population.

“Trying to survive with so many stressors is like carrying a backpack that keeps getting heavier. Eventually, it becomes too much to bear,” said Sarah Teman, lead author of the study and UW PhD student working with UW Professor, Kristin Laidre. “By studying allostatic load, we can understand how much ‘weight’ each bear is carrying, and how that affects populations.”

The scientists measured allostatic load through a suite of samples collected from polar bears during annual population health assessments. This involved analyzing blood samples to assess metabolism, fluid balance, organ function, and immune cells, along with hair samples to measure cortisol, a stress hormone.

Three polar bears pictured walking on rocky ground with clumps of snow.
USGS
A family of polar bears on Barter Island, Alaska.

One finding stood out to the team: adult females that summer on land have higher allostatic load than those that remain on the sea ice. This may be driven by onshore food sources that fail to meet their nutritional needs, coupled with immune stress. The number of adult females summering on land has tripled over the last few decades, as the length of the sea ice melt season has increased.

Other findings contradicted the scientists’ predictions. For instance, they found no overall trend of increasing allostatic load across the population. However, at the individual level, allostatic load fluctuated—rising in some bears over time, while decreasing in others. This suggests that allostatic load may be best understood through individual monitoring. The next step is to link measures of individual health to population vital rates, such as reproductive success.

“Now more than ever, it’s important to develop tools to measure polar bear health,” Teman said. “This gives us insight into the stressors they face, and how we can support their survival in a changing Arctic.”

Read the paper published in Conservation Physiology

For more information, contact Sarah Teman at steman@uw.edu

SAFS hosts 20th working meeting of the Polar Bear Specialist Group, co-chaired by Kristin Laidre

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A meeting of the IUCN/SSC Polar Bear Specialist Group (PBSG) was held at SAFS on 10-14 June 2024, co-chaired by Professor Kristin Laidre, together with Nick Lunn from Canada. Some of the key outcomes of the 20th working meeting of this group were:

  • Recognition of a new subpopulation of polar bears – the Southeast Greenland subpopulation – which has been recently identified as the most isolated and genetically distinct in the world.
  • Updating of the status of four other subpopulations based on new information. The listing of polar bears as Vulnerable under the IUCN Red List will be reviewed in 2025.
  • Discussion about the new harvest management system in Nunavut, Canada, which affects two-thirds of the global population of polar bears, and is a potentially unsustainable management practice.
  • Discussion of the impact of loss of sea ice on polar bears, which is their primary threat, and the scientific need for polar bear location data, only attainable by capture and deployment of tracking devices, to support conservation efforts.

You can read the full press release from the working meeting of the IUCN/SSC Polar Bear Specialist Group, published on June 18, 2024, on their website.

Kristin Laidre
The loss of sea ice is the primary threat to polar bears.