Grizzly Bear Ecology Research

Three people squatting behind a bear laying down.

We’ve been fortunate to work with wonderful state and federal field biologists in many locations to study bear ecology, primarily grizzly bears but occasionally other species. These studies have ranged from understanding the nutritional challenges faced by Yellowstone grizzly bears as their food resources change due largely to man’s impact, to quantifying the importance of salmon to grizzly bears that historically lived in Washington, Oregon and Idaho as compared to their current importance to Alaskan grizzly bears, to what are the current impacts on polar bears as Arctic ice retreats due to climate change.  Many of these studies combined information generated on both wild and captive bears to give greater insight and understanding than either alone could have provided.

Current examples of our field studies are ones that two of our PhD students are conducting in Katmai National Park, one of the most beautiful national parks in Alaska that is famous for large brown bears. Preserving National Parks and their resources for future generations means understanding how such ecosystems function. In Katmai, we are studying how bears use different habitats, such as sedge meadows and intertidal areas, to determine which resources bears rely on most heavily and how those resources influence bear productivity. We have used many methods to answer our questions, including resource selection analyses using GPS collar locations, behavioral observations, analyses of video collar data, diet determination using stable isotopes, and measuring changes in body mass and fat content for bears using different resources. While visitation to Katmai continues to increase, we are also interested in the role humans play in affecting bear use of the landscape. We are currently using time-lapse photography to document patterns in visitation and how the bears’ use of space might differ under varying levels of human use. The results of these studies are important from the practical perspective of understanding how changing environmental conditions, like ocean acidification and threats like oil spills, might affect coastal brown bears. The results are also important for helping the park to understand how to simultaneously maintain ecological functions and visitor enjoyment.

Multiple bears in field.

In the second study we are investigating gene flow throughout the national park and in surrounding areas where hunting is permitted. Understanding how these animals move and how the populations are divided will help managers make decisions that ensure the long-term conservation of these incredible animals. Additionally, this data can be used to examine impacts from increasing visitation to the resident bears. Throughout Alaska and the global range of the eight extant bear species, wildlife viewing has been rapidly increasing in popularity. As more visitors come to far-flung areas such as Katmai, we want to understand the impact of those visitors on the bears. Past and current research at the WSU Bear Center has examined overt behavioral changes due to the presence of humans, but we are now beginning to look at the genetic level. Using genetic techniques, we can determine if human use of specific areas excludes a portion of the population from primary feeding sites and impacts movement throughout the park. This information is increasingly important in making management decisions.

Related field ecology studies publications

Bear carrying salmon in its mouth.

One of the first studies that we did with grizzly bears was to ask how important were salmon historically to grizzly bears in Washington, Oregon, and Idaho when there were still millions of salmon spawning in Northwest rivers.  This is an important question when we think about restoring grizzly bear populations in central Idaho and the North Cascades of Washington where salmon populations currently are quite depleted. There are many historical accounts of bears eating salmon in these areas, but how could we actually quantify the amount or importance of salmon that bears actually ate a hundred years ago?  Fortunately, we have been able to use the captive bears to develop techniques that we can use to answer those questions.  Surprisingly, the techniques that we’ve developed require only a few hairs or a chip of bone from bears killed long ago in which the pelt or skull was preserved in a museum, such as the Smithsonian. By actually quantifying the unique atoms of nitrogen and carbon that come from salmon as compared to all of the other foods that bears eat, we now know that salmon provided an average of 58% of the nourishment for grizzly bears in the 3 northwest states, and for some bears as much 90% of their nourishment came from salmon.

In more recent studies, we’ve compared those values to bear diets in places like Kodiak, Alaska where salmon runs may be near historical levels.  For Kodiak bears, salmon provides 48% of the annual nourishment for adult females and 68% for adult males, so very similar to the average for bears that once lived in Washington, Oregon, and Idaho.  This insight is a good indication of how much Northwest aquatic and terrestrial ecosystems have changed in the past 150 years and what has been lost. Fortunately, there are many populations of grizzlies that subsist almost entirely on plant-based foods, such as berries, forbs, grasses, and roots.  Thus, while there is still enough food in Northwest wildernesses to support healthy grizzly bear populations, the density and productivity of the populations will be only a fraction of what would occur if there were still healthy, wild salmon runs in the rivers of Washington, Oregon, and Idaho.

School of salmon in river.

While we’ve always thought of salmon as a wonderful bear food based on Alaskan experiences, salmon in the rivers south of the Canadian border also carry a disease that affects dogs, coyotes, and bears.  That disease is known as salmon poisoning disease.  The salmon aren’t really poisonous, but they carry a parasite that hatches when consumed by a bear or dog. The parasite implants into the lining of the bear’s digestive tract, and releases a bacteria into the bear’s circulation.  In dogs if left untreated, the bacteria kills 90% of those unlucky enough to have eaten any portion of an infected salmon. Fortunately, bears are not affected by that form of the bacteria, but they are susceptible to a new species of that bacteria that occurs widely in Asia and was first reported in Washington in the early 1970s. While the new bacteria makes bears sick for a few days to weeks, it does not appear to kill them. Thus, if Northwest fisheries managers are able to recover salmon populations, relocated grizzly bears in Washington and Idaho will be able to make use of them.

Related salmon studies publications

DNA chain.

Bears are fascinating from a genetic perspective. Grizzly bears experience three major physiological shifts during a year – active season, hyperphagia and hibernation. These physiological states are characterized by both varying food intake and physical activity.  We are studying the transcriptional response to seasonal changes in grizzly bears in order to understand these physiological changes both from a basic biological viewpoint and in an effort to find new treatments for common human diseases (i.e. obesity and muscle atrophy). RNA-sequencing of multiple tissues is revealing complex regulatory changes that may allow the grizzly bear to achieve such extreme physiological changes every year with no apparent ill effects. In addition to understanding these annual changes, we are interested in the impact human activities (i.e. tourism) have on natural populations of brown bears in popular bear viewing locations.  Recent and historical gene flow helps us understand how populations of brown bears have moved through large areas and has allowed us to get a better understanding of the impact that human use has on bears both within and around Katmai National Park, Alaska.

Related grizzly bear genetic research publications

Insulin Resistance Studies

Insulin studies in blood sample.

Bears undergo a dramatic yearly cycle of weight gain and weight loss. Weight gain in the fall produces bears that would be considered morbidly obese by human standards. Obese humans often develop Type-2 diabetes (T2D) which is associated with insulin resistance. Bears also become insulin resistant during hibernation, but they do not develop glucose intolerance seen in T2D. Importantly, the insulin resistance is naturally reversible. Thus, understanding how insulin and glucose are produced and used by bears throughout the year is a major goal. We have confirmed that bears become insulin resistant in hibernation and currently use a variety of approaches, including culture of bear, mouse and human fat cells to understand the molecular processes involved. For example, cultured fat cells from hibernating bears retain their insulin resistance, which can be reversed by culturing the cells in serum collected from the active season. Identifying the serum components and cellular process involved in this reversal could lead to the development of novel therapeutics for the treatment of T2D.

Circadian Rhythm Studies

Most physiological processes occur on a rhythmic basis. For example, sleep-wake cycles are common to all mammals. These cycles are produced by the body as a result of a molecular “clock” operating in virtually all cells of the body. But how these daily rhythms are coordinated and function seamlessly together is not completely understood. Nevertheless, having functional clocks is vital to maintaining normal physiology. Indeed, obesity, diabetes, and many other disorders are well known to be associated with disrupted rhythms. Given the unique physiological adaptations of hibernation, numerous researchers have asked, “Does the clock continue to tick in hibernation?” The answer for many small hibernators appears to be no. However, by working with our captive bears and with biologists in Canada and Montana that gave us access to wild bears, we have shown that all grizzly bears irrespective of their living condition maintain a functioning circadian clock during hibernation. Thus, the unique ability to both hibernate and maintain a functional clock may indicate novel roles for the clock in the regulation of metabolism and behavior in bears. We hope to learn how the clock and metabolic suppression during hibernation are linked.

Related grizzly bear hibernation physiology studies publications

Researchers checking Polar Bear's vitals and running tests.

We are in the early stages of initiating polar bear studies.  These studies will be similar to our grizzly bear studies in which we want to understand the value of different foods and environments.  These studies are being driven by climate change and the melting of Arctic Ocean ice.  That melting forces bears in many populations onto land during the summer and early fall where food resources are very limited in quantity and quality compared to the seal and other marine mammal populations that normally nourish polar bears.

Related polar bear studies publications

Food is particularly important to bears during the active time of the year because they have to store enough energy as fat to hibernate. During hibernation, females give birth to cubs in January when they haven’t eaten for at least 2 months and will not eat again until at least April or later. We’ve determined that the fattest females produce the fastest growing cubs that also have the best chance of survival.  Similarly, the biggest males do most of the breeding.  Thus, bear foraging and habitat occupancy decisions are probably closely tied to maximizing energy intake while minimizing energy expenditures. In order to understand these decisions from the bear’s perspective as they use man-altered environments, we’ve been measuring activity, weight gain, food utilization, and energy expenditure in a wide range of studies. Many of these studies combine measurements on both wild bears, which allow us to understand the ecological context of the bear’s foraging and habitat use decisions, and captive bears, which are used in studies where we can control many of the variables to not just describe what wild bears are doing, but understand the reason for their decisions.

Mama bear with two cubs in field.

We are using methods developed to measure energy expenditure (calories) of humans and are adapting them for use with both captive and wild bears.  Recently, we modified a horse treadmill and trained both grizzly bears and polar bears to walk on it while we measured their energy expenditure (see video).  As you can imagine, bears don’t work for free, so we feed them their favorite treats while they are exercising on the treadmill. Measurements of energy expenditure in humans and many other more tractable animals use masks or other devices to collect respired air, but of course grizzly bears will not wear a mask.  So, we encased the treadmill in a polycarbonate box and continuously pull air through the treadmill and box. Small samples of that air are taken to determine energy expenditure.  The front and back of the treadmill can be raised or lowered so we can measure the costs of bears walking on level ground and up and down hills.

We are in the early stages of actually measuring the energy expenditure of wild bears and understanding how that relates to movement patterns, rates of gain or loss, and food utilization. We are using a wide range of techniques to accomplish these measurements, such as monitoring heart rate with the same implanted cardiac monitors used on people, quantifying activity with Fitbit-type activity sensors, using camera collars to quantify behavior and see what the bears are eating, and by actually measuring oxygen consumption through the use of doubly-labeled water.  This information is being used to help us understand competition between grizzly bears and polar bears, estimate required food intake to achieve specific levels of productivity, understand why some foods and habitats are more preferred than others, and understand the energy costs of various travel paths as they move through their environment, particularly as affected by human activities.

Related energetic studies publications