As a conservation biologist, I am tasked with developing a thorough understanding of threatened species and sharing what I learn, so that we can do a better job of protecting them. Toward this end, I feel very lucky to have spent the past 25 years of my life working in some of the most remote and beautiful places on earth.
At this point in my career, my own internal clock is tuned to the life cycles of the species I study. This time of year, all I can think about is polar bear dens and the beautiful, dark blue fjords and stark, snowy mountains of Norway’s Svalbard archipelago. Svalbard sits at the top of world and is home to an extraordinary array of Arctic marine mammals, including narwhal, orcas and, of course, polar bears. Svalbard is also a critical “nursery” area for polar bears of the high Arctic, and its steep slopes are dotted with polar bear dens. Unfortunately, as in other areas of the Arctic, climate change-driven sea ice losses are impacting polar bear denning patterns, and fewer maternal bears appear to making it to this once-ideal habitat. For those that do still den here, protecting denning habitat is more important than ever.
The challenges of studying polar bear dens are pretty extreme. Dens lie under 3 to 4 feet of snow, and thus are not really visible to the human eye. Our task is like an extreme version of an Easter egg hunt—but fortunately, new developments in tracking technologies mean that we can estimate the locations of dens by using polar bear tracking tags. Once they are located, our team deploys a combination of customized and off-the-shelf video surveillance equipment to remotely observe mothers and their cubs when they emerge from dens—while staying a good distance away.
The importance of maternal denning to polar bears can’t be understated. Unlike grizzly and black bears, only pregnant female polar bears den. Pregnant females will dig their own maternity dens in the snow during the late fall, where they give birth to their tiny and completely helpless cubs about one month later. The mom and cubs will emerge from the den about three to four months later.
Once out of the den, life for polar bear cubs changes dramatically, as they must follow their mother out onto the sea ice in a never-ending search for the fat-rich seals that polar bears depend on. This rapid shift from being a completely helpless newborn to being ready to walk (and sometimes swim) in the Arctic cold is truly extraordinary! With so little time to mature, polar bear cubs need every minute they can get in the warmth and security of the den to feed and rest.
Climate change poses a profound threat to successful maternal denning, and to cub survival. With Arctic temperatures warming at about three times the global average, the capacity for polar bears to successfully hunt for seals is challenged. This may, in turn, influence the stored body fat of pregnant females before they go into the den—and it may prompt them to emerge from dens earlier. If this the case, young cubs may be forced to begin their lives outside the den before they are ready.
The polar bear’s habitat is disappearing. Arctic sea ice, on which the polar bear depends for all of its critical life functions, has diminished by 25% in the last 40 years. This habitat loss has driven declines in body condition, reproduction and population size within some polar bear populations. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species currently classifies the polar bear as Vulnerable to extinction throughout its range. But for many of the regional subpopulations, there is insufficient data to estimate population size or trends. Further, because sea ice losses are expected to intensify in the coming decades, the IUCN Polar Bear Specialist Group has estimated a further 40% decline in polar bear numbers over the next 30 years.
The goals of San Diego Zoo Global’s polar bear conservation program are to assess and mitigate the impacts of rapid environmental change on polar bears through projects that are focused on the most critical and vulnerable stages of their life cycle. Because the challenges to polar bears are so great, San Diego Zoo Global collaborates with Polar Bears International and other institutional partners across the circumpolar Arctic.
Megan Owen, Ph.D., is the director of Population Sustainability at the San Diego Zoo Institute for Conservation Research. Read her previous blog, An Enduring Conservation Legacy: The San Diego Zoo Panda Team.