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  Behavioral Education for Human, Animal,
Vegetation & Ecosystem Management

Stories of Applied Animal Behavior
Created by members of a graduate Foraging Ecology Class
     at the University of Idaho and Washington State University
     under the direction of Drs. Karen Launchbaugh and Lisa Shipley

Diet-Mixing by Brown and Black Bears

By Jennifer Fortin, M. S. Candidate, School of Biological Sciences, Washington State University

Human Disturbance

   Ecotourism accounts for a large proportion of economic income in many wilderness areas, including Alaska.  Fishing, bear viewing, and hunting draws millions of people to Alaska each year.  Historically, it is believed that brown and black bears either become habituated to human presence or are displaced by ecotourism.  Despite the effects of human disturbance on wildlife, there has not been a study regarding the effects on brown and black bears in Alaska.  

    At Glacier Creek, Kenai Peninsula, Alaska, there is an undisturbed population of brown and black bears.  At this site, preliminary results from a disturbance study showed that brown bears, collared with GPS units to track their locations, avoid the section of the creek while humans are present and for a few weeks afterward.  With controlled ecotourism, it is unknown what effect human disturbance will have on behavior, however if bears avoid human presence, they will be detrimentally affected nutritionally.  

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    Possible detrimental effects of ecotourism on bear nutrition are as follows: a decrease in the amount of time spent by bears on salmon streams, a decrease in salmon availability, a possible decrease in overall dietary meat intake and an increase in time spent foraging for berries.  To gain the necessary protein and energy by feeding only on berries, the time and energy spent foraging would have to increase.  Due top the social hierarchy of bears, if larger brown bears are increasing their time foraging for berries this could displace black bears and sub adult brown bears from that food resource.  On the other hand, if bears become habituated and lose their fear of humans, then the chances of bear-human interactions increase.  Regardless, people will need to be taught the proper methods of food storage, especially salmon they catch, to minimize risk to both humans and bears.

Nutritional Value of Food Resources

   Brown and black bears vary their diets seasonally.  Upon emergence from hibernation, bears usually feed upon forbs and any terrestrial meat available.  Forbs are broad-leaved herbs other than grasses and are chosen over grasses because they are a more digestible protein source.  Upon arrival of salmon and production of berries in the summer and fall months, bears turn to these sources to meet their nutritional needs and gain body mass.

   When salmon and berries are available, salmon is eaten preferentially by brown bears because salmon contain high amounts of protein.  Berries are utilized more often and earlier in the season by black bears for two reasons.  First, black bears are smaller than brown bears; therefore they are more able to meet their energetic needs consuming berries.  Second, black bears are excluded at salmon streams by brown bears.  Berries contain from 3-7 % protein while salmon has about 69%, based on dried samples.  For spawning sockeye salmon, the protein, fat, and energy levels are higher in the reproductive organs than in the rest of the bodily tissue and higher in females than males.  This supports the idea that brown bears preferentially consume females that have not yet spawned for the roe because of the higher fat, energy, and protein content.

   The mixing of diets by brown bears results in different gains in body composition.  Diets containing high-protein contents primarily lead to a gain in lean body mass, which is important in replacing weight lost during hibernation.  A low-protein, high-energy diet primarily results in fat gain.  As salmon becomes available in the summer months, bears move to this high-protein food source.  Later in the summer, as berries become available, bears incorporate both food sources into their diet. Diet mixing occurs seasonally in most wild bear populations.  One explanation for this may be that the maintenance energy cost for brown bears varies with the level of dietary protein, with minimal costs ranging from 20-40% dietary protein.

Learning of Diet Mixing

Social Learning

    As has been shown in most mammals, brown and black bear cubs learn what food sources to use and how to use them primarily from their mothers and secondarily from peers.  For the first two to three years of a bear's life cubs follow their mother while she forages and fishes for salmon, imitating her and consuming what she chooses.  During these initial years, bears learn to feed on salmon, terrestrial meat, forbs, and berries.

    After the initial years with the sow, subadult bears, three to five years of age, often travel in small groups.  During this period they have many new experiences, trying to learn where they fit into the social system, and learn from their peers.  Subadults play with each other, learning how to fight, which is vital for survival.  As they age and approach sexual maturity, bears become solitary with the exception of breeding season.

Individual Learning

    After brown and black bears are full-grown they are primarily solitary, continuing to learn from individual experience.  Males wander until they are large enough to establish their own territory, normally encompassing female territories, in order to breed.  During this time, male brown bears learn to avoid dominant males to survive.  Adult male and female black bears learn to avoid food sources that are occupied by brown bears, therefore, black bears often only use salmon streams when brown bears are absent.


    Although food abundance and social structure determines a large part of what a food is available to bears, they also make decisions based on the innate ability to determine nutritional value.  Animals receive positive or negative feedback after consuming a food resource that leads to preferences and aversions.  The positive feedback brown bears receive may vary with the time of year and the type of body mass gain needed.  Brown bears need to add lean body mass when they are growing and upon emergence from hibernation in the spring.  Fat gain is important in the fall period of hyperphagia, a period of increased food intake, for survival through hibernation, especially for a female to support cubs.


   Habituation of bears to humans on salmon streams can increase the number of bear-human interactions.  If anglers are irresponsible by fishing to close to bears or are not storing their catches properly, bears will learn to associate humans with salmon.  The association of food with humans is a main cause of damage to life and property by bears, which ultimately leads to bear fatalities.  Ecotourism needs to be properly managed with education for human users, to prevent unnecessary conflict.  Management often involves limitations of fishing locations to avoid prime areas of bear use and proper regulations for bear encounters.  Regulations may include not fishing within a predefined distance of a bear, cutting the fishing line if a bear approaches a hooked salmon, and storing any food in bear proof containers.  All of these approaches improve the safety of both humans and bears.  

    Avoidance can be a larger concern than habituation because it may decrease the dietary nutrition of bears.  Studies need to take place to see if avoidance is occurring or if bears will adjust to human presence.  If bears will not fish where humans are located then it is important to limit the time that humans spend on the salmon stream.  In Alaska, where it is light almost 24 hours a day in the summer, people tend to fish at all hours.  Bears must be given a certain amount of light with no human presence so that they can catch enough fish to sustain themselves.

Literature Cited

Farley, S., G. Hilderbrand, G. Del Frate, T. Bailey, R. Ernst, L. Suring, W. Shuster, M. Tetreau, and J. Schoen. 2001. A conservation assessment of the Kenai Peninsula brown bear. K. L. Lew (ed). Alaska Department Fish and Game.

Gende, S. M., T. P. Quinn, M. F. Willson. 2001. Consumption choice by bears feeding on salmon. Oecologia 127: 372-382.

Hilderbrand, G. V., S. G. Jenkins, C. C. Schwartz, T. A. Hanley, and C. T. Robbins. 1999a. Effect of seasonal differences in dietary meat intake on changes in body mass and composition in wild and captive brown bears.  Canadian Journal of Zoology 77: 1623-1630.

Jacoby, M. E., G. V. Hilderbrand, C. Servheen, C. C. Schwartz, S. M. Arthur, T. A. Hanley, C. T. Robbins, and R. Michener. 1999. Trophic relations of brown and black bears in several western North American ecosystems. Journal of Wildlife Management 63: 921-929.

Rode, K. D., and C. T. Robbins. 2000. Why bears consume mixed diets during fruit abundance. Canadian Journal of Zoology 78: 1640-1645.

Rode, K. D., and L. A. Shipley. 2001. Constraints on herbivory by grizzly bears. Oecologia 128: 62-71.  

Titus, K., J. N. Trent, L. K. Aumiller, J. H. Westlund, and M. Sigman. 1994. Managing brown bears as both game and non-game past experience and future prospects.  Transcript 59 North American Wildlife and NR Conference

Welch, C. A., J. Keay, K. C. Kendall, and C. T. Robbins. 1997. Constraints on frugivory by bears. Ecology 78: 1105-1119.

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