American Bears

THE LARGEST LIVING TERRESTRIAL CARNIVORES

BEAR ECOLOGY

North America is home to three species of the world’s largest terrestrial carnivore. Find out more…

THREATS TO BEARS

From fragmentation and loss of habitat to poaching, bears face a number of challenges. Find out more…

ECOLOGICAL ROLE

As with many large carnivores, bears play a positive role in maintaining ecosystem health and integrity. Find out more…

COEXISTING

Tips to reduce conflicts when humans and bears share an ecosystem, and promote coexistence. Find out more…

ECOLOGY OF THE AMERICAN BLACK BEAR (URSUS AMERICANUS) AND GRIZZLY BEAR (URSUS ARCTOS)

EVOLUTION

The fossil record of the bear family (Ursidae) began to appear in the Miocene Epoch around 23 million years ago (Britannica, n.d.; Burt & Grossenheider, 1976; Nowak, 1999). Since that time, bears have evolved to become the largest living terrestrial carnivore around the globe (Burt & Grossenheider, 1976). North America is home to three different species of bear: black bears (Ursus americanus); brown bears, also called the grizzly bear (Ursus arctos); and polar bears (Ursus maritimus). This discussion will focus on black and grizzly bears.

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Feature photo: Black Bear in Kings Canyon National Park by Deb Etheredge via Creative Commons Above photo: Grizzly Bear in Alaska by Princess Lodges via Creative Commons

DISTRIBUTION

Overall, bear habitats comprise many ecosystems and range from tropical forests to arctic ice flows (Krause, et al, 2008; Nowak 1999; Schwartz, 2012).  In a more general sense, black bears prefer forested regions whereas grizzly bears seem to prefer open areas such as tundra, alpine meadows, and coastline (Nowak, 1999).

Black Bear Distribution

The pre-European settlement distribution of black bears ranged from Mexico to Alaska and from the Atlantic Ocean to the Pacific Ocean (Unger, et al, 2013). Black bear populations have expanded and contracted over the years in many areas. Fortunately, many reintroduction programs have successfully re-established them into states where they were previously extirpated. Today they can be found in 40 of 50 U.S. states and in all the provinces and territories of Canada except Prince Edward Island (BearSmart.com, n.d.). In some cases, the black bear has extended its range in areas where the grizzly bear has been exterminated, such as the mountains of southern California, the Trans Pecos region of Texas, and parts of the Canadian tundra (Unger, et al, 2013; Nowak 1999). The surviving black bears of Louisiana and Florida are a unique subspecies and are on the federal list of threatened species (defenders.org, 2012).

Grizzly Bear Distribution

Historically, grizzly bears in North America ranged from Alaska to Mexico and California to the Dakotas. Some speculate they were also common in the Great Plains prior to Europeans arriving (Nationalgeographic.com, n.d.; Nowak, 1999). Today, grizzly bear home ranges have greatly diminished. In Canada they are found in Alberta, British Columbia, Yukon, and the Northwest territories. In the U.S., their range includes Alaska, Wyoming, Montana, Idaho, and Washington (BearSmart.com, n.d.). The United States has listed grizzly bears as threatened under the Endangered Species Act. In Canada, great concern surrounds the health of grizzly bear populations, leaving certain provinces to list them as threatened (Schwartz, et al., 2012).

Grizzly bears often grow much larger along the coastal areas of Alaska and Canada, leading scientists to further separate them into distinct geographic sub-species. These larger bears are called Kodiak bears or Alaskan (big) brown bears (BearSmart.com, n.d.; Burt & Grossenheider, 1976; Nowak, 1999). Furthermore, the smaller grizzly bears who manage to survive the cold, treeless, wilderness in Canada’s western arctic are called barren ground grizzly bears (Struzik, 2006).

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Above photo: Grizzly Bears in Blueberries by Jacob W. Frank for Denali National Park Service via Creative Commons. 

SOCIAL STRUCTURE

Bears are individualists by nature, except for females with young and congregations of bears at sites with large caches of food. Consequently, a large majority of a bear’s life is sometimes spent wandering alone or hibernating. This does not mean they are asocial or do not have social interactions with other bears. Dominance hierarchies are often formed amongst familiar bears, especially if a large amount of food is concentrated in one area. Some bears seemingly get along better with other bears and some do not tolerate each other. Contrary to the way they are sometimes portrayed, they are usually peaceful animals who try to avoid conflict. (BearSmart.com, n.d.; Nowak, 1999).

As winter approaches, bears begin to gain weight until it is time to hibernate. Both black and grizzly bears undergo true mammalian hibernation. Hibernation is an adaptation to seasonal food shortages, low temperatures and snow cover on the ground. The physiological processes of hibernation can differ depending on the species of mammal. With bears, respirations decrease from 6-10 breaths per minute to one breath every 45 seconds; metabolic rate is decreased 50 to 60 percent; heart rate drops from 40-50 beats per minute to 8-19 beats per minute; and body temperature drops from 38 degrees Celsius to 31 degrees Celsius. Both grizzly bears and black bears do not eat, drink, defecate, or urinate during hibernation. In order to survive during this long slumber, they live off the fat stores in their body which depletes up to 15-30% of their body weight. Furthermore, waste products are recycled when urea is catabolized into nitrogen. This nitrogen is used to build protein for maintaining muscle mass and organ tissue (USNPS, 2015).

Other physiological processes are also altered while bears are sleeping. For instance, bears continue to produce feces during hibernation; however, the feces will form a plug in the anus to prevent the bear from defecating in the den site. Also, while most mammalian species experience osteoporosis from being in a non-weight bearing position for an extended period of time, bears do not. Furthermore, a bear’s cholesterol will double during hibernation; however they don’t suffer from the same hardening of the arteries or gallstones as a human would during this period of hypercholesterolemia (USNPS, 2015).

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Black Bear Social Structure

Socially, when not hibernating, black bear behavior is linked to plant growth, fruiting, and availability of food. In general however, they tend to avoid one another and will often defend their territory from other bears or intruders. Other black bear behavioral characteristics include the display of a variety of vocalizations including a “woof” sound when startled, a loud growl when fighting, or a shrill howl by cubs when lonely or frightened (Burt & Grossenheider, 1976; Nowak, 1999).

Female black bears reach sexual maturity at the age of four to five years and males reach sexual maturity between five and six years of age. Mating season usually peaks between June and mid-July. Individual females are in estrus for only 1-3 days during this time. Females generally give birth every other year but sometimes wait 3-4 years. Pregnancy lasts 220 days. However, delayed implantation causes embryonic development to start in the autumn and lasts only ten weeks. Births occur in January and February, often during hibernation (Nowak, 1999).

Depending on the climate of a particular area, black bear hibernation can occur as early as late September and can last as long as May. Their sleep is only interrupted by an occasional journey out of their den during periods of warm weather. Den sites are usually composed of fallen trees, hollow logs or trees, or burrows. Litter size in black bears can range from one to five cubs. Young bears are born with their eyes closed. Weaning occurs around 6-8 months (Defenders.org, 2012.; Burt & Grossenheider, 1976; Nowak, 1999).

In order to avoid aggressive adult males in the breeding season, the mother and cubs will depart the den site in the spring. Cubs will remain with their mother into the second winter. Mothers usually tolerate their offspring within their territories and will allow their daughters to incorporate portions for their own. Young males disperse an average of sixty-one kilometers from their birth areas. Black bears can sometimes live thirty years or more (BearSmart.com, n.d.; Burt & Grossenheider, 1976; Nowak, 1999).

Grizzly Bear Social Structure

Barring the aggressiveness shown in dominance hierarchies, there is no indication of territorial defense amongst grizzly bears. They will even form family foraging groups of multiple ages where food is plentiful. Female grizzly bears have much smaller home ranges than males but also show the most aggression when they’re with their young. Large adult males are mostly avoided in gatherings and will sometimes kill young bears. The least aggressive bears in the dominance hierarchy are the adolescents (BearSmart.com, n.d., Nowak, 1999).

Grizzly Sow & Yearling Cub Playing 2 

During breeding season male grizzly bears will fight over females. The winner will breed with the female for one to three weeks. Mating takes place from June to July with delayed implantation. The fertilized egg will begin development sometime in October or November. Birth occurs between January and March during hibernation. Each litter can have as little as one cub and as many as four. Cubs are born with their eyes closed. Each cub is weaned at 5 months and remains with the mother through multiple springs (usually no less than two and no more than four). Siblings will often maintain social interactions for several years after leaving their mother. Sexual maturity for both genders is between the ages of four and six. Grizzly bears can sometimes live well past thirty years of age (Nowak, 1999).

Grizzly bear hibernation begins in October and can last through May depending on the locality, weather and the health of the bear. In some southern areas hibernation does not occur. Their dens are made of dry vegetation and usually dug by the bear. Preferred locations are on a sheltered slope under a large rock or under the roots of large trees. These sites are used year after year (Nowak 1999).

Even though grizzly bears prefer more open terrain, they often shelter in dense cover during the day when wandering or foraging. As evening approaches they begin to move and feed, staying active through early morning. The larger bears in coastal Alaska are active throughout the day. Seasonal movements are common in grizzly bears and coincide with food sources like salmon and areas with high berry yield (Nowak 1999).

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Above photos: Grizzly Sow and Yearling by Arthur T. LaBar via Creative Commons, black bear in the woods of California by Wade Tregaskis via Creative Commons and black bear foraging by Barry Alan Farlow via Creative Commons. At left, black bear takes a nap by Marius Strom via Creative Commons.

APPEARANCE

Generally, bears have a large head and heavily built body with short powerful limbs, a short tail and small eyes. Ears appear small, rounded, and erect. Each limb has five digits that end in recurved claws which are used for tearing and digging. They have a well-recognized shuffling gait that is plantigrade (the heel of the foot touches the ground when walking). Most bears can walk short distances on their hind legs. They also have an excellent sense of smell but don’t have a well-developed sense of hearing or sight (Burt & Grossenheider, 1976; Nowak, 1999).

Black Bear Appearance

Characteristically, black bears appear similar in shape and size throughout their range. They have an average head and body length of 1.5-1.8 m, tail length of 12 cm, shoulder height of 91 cm and weights ranging from 92 kg – 270 kg; with males overall being the larger of two genders. Common color variations include black, chocolate brown, and cinnamon brown. Different colors can appear among siblings. White and blue/black pelages also occur but are rare. Black bears can swim and climb and are mostly nocturnal. Irrespective of their night-time activities, black bears will frequently move around at all hours when foraging (BearSmart.com, n.d.; Burt & Grossenheider, 1976; Nowak, 1999).

Grizzly Bear Appearance

On average grizzly bears have a head and body length between 1.7 m and 2.8 m, and shoulder height of 90 cm to 150 cm. Adult males are most often larger than adult females. Depending on the location in which the grizzly bear lives, weights can vary dramatically from as little as 95 kg all the way up to 780 kg for the larger coastal bears. Pelages range from cream to dark brown to almost black. In the Rocky Mountains some bears display white hairs or silvertips on their backs. Grizzly bears can be distinguished from black bears through the appearance of a protuberant hump on their shoulders, a snout that rises sharply into the forehead, longer fur, and longer claws (BearSmart.com, n.d.; Burt & Grossenheider, 1976; Nowak, 1999).

Even though grizzly bears appear slow, they can move very quickly, easily overtaking a black bear on the run (they have been found to reach speeds greater than 30 mph/48 kph with a top speed of 37 mph/59.5 kph) (BearSmart.com, n.d.; Nationalgeographic.com, 2015; Nowak, 1999). They are also extremely strong. Some eyewitness accounts discuss horse and bison carcasses being dragged considerable distances. However, their claws and feet are not adapted for climbing trees like black bears (Nowak, 1999).

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Above photos: Bear comparison with Black Bear on the left by Pat (Cletch) Williams via Creative Commons and the Grizzly Bear on the right by Gregory “Slobirdr” Smith via Creative Commons. Female Grizzly Bear Standing by Heather Johnson via Creative Commons and Cinnamon Black Bear in Yellowstone National Park by Dave Toussaint via Creative Commons.

DIET

Bears spend a lot of time foraging for many different types of foods. The type of food they seek throughout the year changes with the seasons. Typical foraging areas include rivers, streams, sunny south-facing slopes, wetland meadows, river valleys, avalanche slopes, aspen forests, marsh edges, and dumpsites. Since their diet is comprised of both plants and animals they are considered omnivorous. In some cases, plants can make up 90 percent of their diet (BearSmart.com, n.d.).

Black Bear Diet

Three quarters of the black bear diet is composed of fruits and vegetables. This includes fruits, berries, honey, tubers nuts, acorns, grass, sapwood, and roots. The other twenty-five percent of their diet consists of insects, fish, rodents, carrion, eggs, and occasionally other larger mammals. Black bears also commonly consume garbage from dumps (Burt & Grossenheider, 1976; Nowak, 1999).

Grizzly Bear Diet

Grizzly bear diet also consists mainly of vegetation and other animals. During the early spring they forage for overwintered berries, grasses, sedge, roots, mosses, bulbs and other starch rich foods using their long claws to dig when necessary (BearSmart.com, n.d.; Burt & Grossenheider, 1976; Nowak, 1999). As the season progresses this changes to succulents, and perennial forbs. By autumn berries, bulbs and tubers are a main component. In addition to plants, their diet includes ants, beetle larvae and other insects, mice, ground squirrels, marmots, and carrion. Grizzly bears of the Canadian Rockies hunt moose, elk, caribou, mountain sheep, and mountain goats. The grizzly bear is also a competitor with, and predator of, black bears where ranges overlap (BearSmart.com, n.d.; Nowak, 1999).

The contrasting size of Alaska and Pacific Coast brown bears and the smaller grizzly bears of interior North America can be attributed to a diet of anadromous salmon. These coastal bears congregate at greater densities in areas where salmon migrate upstream. They also tend to grow larger than anywhere else in their range (Nowak 1999).

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Above photos: Black bear eating berries by Emily Mocarski via Creative Commons and young black bear foraging by vijay_SRV via Creative Commons. Grizzly Bear digging for food by Elizabeth Haslam via Creative Commons and brown bear eating salmon by Allan Harris via Creative Commons.

THREATS TO BEARS

Due to their large size and distinctive behavior, bears have unique challenges that can make surviving difficult and sometimes tragic. Currently, the largest threat to the North American bear population is man and rural development (Schartz, et al., 2012). For example, during the nineteenth century, wide-spread poisoning of bears and other large carnivores with strychnine was common as people expanded west (Young & Jackson, 1978). In addition, man continues to kill or intensively control bear populations for a multitude of reasons such as fear, sport, cash-crop protection, black-market trading, food, and livestock predation. Fortunately bear predation on livestock is mostly minimal; however, they do extensive damage to beehives, cornfields and other crops (Nowak, 1999). Important conflicts between man and bear include the attraction of bears to urban food sources, and poaching for the medicinal use of bear parts for export to Asia (Bigwildlife.org, 2008; Nationalgeographic.com, 2010; Nowak, 1999).

As urban centers grow and encroach into rural settings, garbage collection centers and dumpsites have become more commonplace near bear habitat. Man-made waste threatens bears in a multitude of ways since edible garbage has been documented as an important food source for bears and has served as an attractant in developed areas (Mathews, et al., 2003). Firstly, the risk of mortality for bears through direct or lethal management actions and bear-vehicle collisions is higher when they forage in and near urban areas (Merkle, et al., 2013). Since bears are opportunistic foragers they will often risk encroachment into many types of urban centers when garbage is readily available. This increases the risk of human-bear conflicts especially in many National Parks where encounters between visitors and bears often arise due to human noncompliance with posted restrictions, such as feeding or approaching bears. A secondary threat to bears arises in the form of traffic accidents as bears cross highways and roads to reach natural food caches and human generated food sources (Mathews et al., 2003; Merkle, et al., 2013; The Wildlife Team, 2003). Roadways, particularly ones with higher traffic volumes, can negatively affect wildlife populations through direct mortality and habitat fragmentation (Sawaya, et al., 2012).

Since bears keep such large home ranges, habitat fragmentation by roadways, highways, and other thoroughfares as it relates to bear management is of particular concern to ecologists. Although accident mortality of bears on highways, streets, and roads is worrisome, researchers have found that barrier effects caused by road avoidance are a much larger ecological problem. For instance, one study indicated that wide ranging, large bodied carnivores such as black bears and grizzly bears are susceptible to road caused population fragmentation due to their low densities, low reproductive rates and large home ranges. In an effort to address this problem, some government run parks, reserves, and wildlife refuges are building man-made land bridges or wildlife crossings to keep wildlife corridors open for animals such as bears (Sawaya, et al., 2012).

One of the more tragic threats to bears, especially black bears in North America is the hunting, killing, and black market trade of bears and their body-parts to various parts of Asia. Unfortunately, the decline of the Asiatic black bear has sparked increased pressure on black bears and other bears globally as their body parts are being used in traditional medicines and foods. Prized black market products include the meat, fat, paws, bones, brain, blood, spinal cord, head, skin, and gallbladder. The gallbladder is a more valuable commodity. Many cultures use it to treat diseases of the liver, heart, and digestive system, as well as to relieve pain, improve vision, and clean toxins from the blood (Nowak, 1999). Some dried bear gallbladders can sell for as much as thirty thousand dollars (Bigwildlife.org, 2008). Discouragingly, this type of trade is still rising in activity. One government restriction offers some protection. Called the Lacey Act, the federal government passed this act in 1900 in an effort to make it unlawful to import, export, sell, acquire, or purchase fish, wildlife, or plants that are taken, transported or sold in violation of U.S. or Native American law. It also covers interstate or foreign commerce involving any fish, wildlife, or plants taken, possessed, or sold in violation of State or foreign law. This was the first federal law protecting wildlife passed in United States (fws.gov, n.d.). Currently, thirty-four states in the U.S. have bans on the trade of bear gallbladders and bile. (Nationalgeographic.com, 2010; Bigwildlife.org, 2008)

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Above photo: Four! Bear cubs about to cross a road near Mammoth Hot Springs by Pat Gaines via Flickr Creative Commons

ECOLOGICAL ROLE OF BEARS

Landscapes are more than a juxtaposition of communities in space. Species are imbedded within complex interaction networks at both local and regional scales…(Mouquet, et al., 2013). As part of our landscape, both black bears and grizzly bears are considered apex predators and co-regulators. Some scientists label them as keystone species as they contribute to nutrient cycling of salmon and carrion, indirectly assist with seed dispersal over large areas, regulate prey species such as ungulates, which in turn leads to increased plant biomass, and assist with soil aeration when digging for roots and rodents. Without keystone species such as bears, the health of our ecosystems would decline affecting forest regeneration, clean water, natural pest control, seed dispersal, disease regulation, climate regulation etc. (Davidsuzuki.org, 2014; Keystoneconservation.us, n.d.; Predatordefense.org, n.d.).

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Above photo: Grizzly bear cleans up what remains of a carcass by Pat Gaines via Creative Commons

TIPS AND TOOLS FOR COEXISTENCE

If you live in an area that has black bear, grizzly bear, or combination of both as part of the surrounding ecosystem, there are numerous steps you can take to reduce conflicts associated with these two species. In addition, various advocacy groups can offer advice on reducing encounters, preventing conflicts, and purchasing equipment to protect livestock and other cash crops from bear damage. If you are a rancher, these organizations will guide you in non-lethal deterrence methods and receiving compensation for losses to livestock (Defenders.org, 2012).

Following these tips can help protect your property, pets and family: storing trash in a secured location, removing bird feeders when bears are in the area, removing fallen fruit from under fruit trees, not feeding pets outdoors, cleaning all food and grease from barbeque grills, using electric fencing to secure crops, animals, and beehives, eliminating pungent food odors from your residence, promoting the use of bear resistant dumpsters in your communities, discouraging the feeding of bears by visitors, tourists or neighbors, and simply just leaving bears alone (Westernwildlife.org, n.d.; ncwildlife.org, n.d.; Schwartz, et al., 2012). Lastly, if you are camping, hiking, or enjoying the outdoors in any way that overlaps bear territory, carrying bear spray, talking to park rangers and following local bear country rules and regulations will go a long way in ensuring a safe and enjoyable outing (westernwildlife.org, n.d.).

As humans encroach further upon bear habitat the need to understand the importance of bears in our ecosystem becomes ever more critical. Their survival ultimately depends on our tolerance for them around our living spaces. Having a bear management plan, involving communities’ leaders in critical decisions that reduce bear conflicts, and creating educational outreach programs are all ways in which we can promote non-lethal co-existence with one of our most important North American carnivores (Schwartz, et al., 2012).

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Above photo: Black bear in trash can by Florida Fish and Wildlife and dumpster diving black bear by Jim Mullhaupt via Flickr Creative Commons.

LITERATURE CITED

1. Brown Bear Species Profile, Alaska Department of Fish and Game. (n.d.). Retrieved July 21, 2015, from http://www.adfg.alaska.gov/index.cfm?adfg=brownbear.main

2. Boulanger, J., Cattet, M., Nielsen, S.E., Stenhouse, G., Cranston, J. (2013). Use of Multistate Models to Explore Relationships Between Changes in Body Condition, Habitat, and Survival of Grizzly Bears Ursus Arctos Horribilis. Wildlife Biology, 19:3

3. Burt, W., & Grossenheider, R. (1976). A field guide to the mammals: Field marks of all North American species found north of Mexico (3d ed.). Boston, New York: Houghton Mifflin.

4. Basic Facts about Black Bears. (2012, February 24). Retrieved July 22, 2015, from http://www.defenders.org/black-bear/basic-facts

5. Cronin, M.A., McDonough, M.M., Huynh, H.M., Baker, R.J. (2013). Genetic Relationships if North American Bears (Ursus) Inferred from Amplified Fragment Length Polymorphisms and Mitochondrial DNA Sequences. Canadian Journal of Zoology 91: 626-634.

6. Dubois, S., Fraser, D. (2013). Local Attitudes towards Bear Management after Illegal Feeding and Problem Bear Activity. Animals 3: 935-950

7. Coexisitng with Black Bears. (n.d.). Retrieved July 21, 2015, from http://www.ncwildlife.org/portals/0/Learning/documents/Species/CoexistWithBears.pdf

8. Grizzly bears. (2014). Retrieved July 21, 2015, from http://www.davidsuzuki.org/issues/wildlife-habitat/science/critical-species/grizzly-bears/

9. Grizzly Bears, Grizzly Bear Pictures, Grizzly Bear Facts – National Geographic. (n.d.). Retrieved July 21, 2015, from http://animals.nationalgeographic.com/animals/mammals/grizzly-bear/

10. Grizzly Biology & Behavior – Western Wildlife Outreach. (n.d.). Retrieved July 21, 2015, from http://westernwildlife.org/grizzly-bear-outreach-project/biology-behavior/

11. Herrero, S. (n.d.) Conflicts Between Man and Grizzly Bears in the National Parks of North America. Third International Conference on Bears. Retrieved 21 July 2015, from http://www.bearbiology.com/fileadmin/tpl/Downloads/URSUS/Vol_3/SHerrero_Vol_3.pdf

12. Immell, D., Jackson, D.H., Boulay, M.C. (2014). Home-Range Size and Subadult Dispersal of Balck Bears in the Cascade Range of Western Oregon. Western North American Naturalist 74(3): 343-348.

13. Krause, J., Unger, T., Nocon, A., Malaspinas, A-S., Kolokotonis, S-O., Stiller, M., Soibelzon, L., Spriggs, H., Dear, P.H., Briggs, A.W., Bray, S., O’Brien, S.J., Rabeder, G., Matheus, P., Cooper, A., Slatkin, M., Paabo, S., Hofreiter, M. (2008). Mitochondrial Genomes Reveal An Explosive Radiation of Extinct and Extant Bears near the Miocene-Pliocene Boundary. BMC Evolutionary Biology 8:220

14. Lacey Act. (n.d.). Retrieved September 6, 2015, from http://www.fws.gov/international/laws-treaties-agreements/us-conservation-laws/lacey-act.html

15. Living with Wildlife in the Northern Rockies: Coexisting with Grizzly Bears. (2012, August 29). Retrieved July 17, 2015, from http://www.defenders.org/sites/default/files/publications/coexisting-with-grizzly-bears-in-northern-rockies.pdf

16. Mathews, S.M., Greenleaf, S.S., Leithead, H.M., Beecham, J.J., Quigley, H.B. (2003). Final Report: Bear Element Assessment Focused on Human-Bear Conflicts in Yosemite National Park. Hornocker Wildlife Institute

17. Merkle, J.A., Robinson, H.S., Krausman, P.R., Alaback, P. (2013) Food Availability and Foraging Near Human Developments by Black Bears. Journal of Mammalogy, 94 (2) 378-385

18. Miocene Epoch | geochronology. (n.d.). Retrieved July 21, 2015, from http://www.britannica.com/science/Miocene-Epoch

19. Mouquet, N., Gravel, D., Massol, F., Calcagno, V. (2013). Extending the Concept of Keystone Species to Communities and Ecosystems. Ecology Letters, 16, 1-8

20. North America’s Bears | Types of Bears – BearSmart.com. (n.d.). Retrieved July 21, 2015, from http://www.bearsmart.com/about-bears/north-americas-bears/ 21. Nowak, R. (1999). Walker’s Mammals of the World (6th ed.). Baltimore: Johns Hopkins University Press.

22. Rovang, S., Neilsen, S.E., Stenhouse, G. (2014) Detectibility of Fixed Hair Trap DNA Methods in Grizzly Bear Population Monitoring. Wildlife Biology 21: 68-79

23. Sawaya, M.A., Clevenger, A.P., Kalinowski, S.T. (2013). Demographic Connectivity for Ursid Populations at Wildlife Crossing Structures in Banff National Park. Conservation Biology, 27(4), 721-730.

24. Schwartz, C.C., Gude, P.H., Landenburger, L., Haroldson, M.A., Podruzny, S. (2012). Impacts of Rural Development on Yellowstone Wildlife: Linking Grizzly Bear Ursus arctos Demographics with projected residential Growth. Wildlife Biology 18: 246-257.

25. Spady, T.J., Lindburg, D.G., Durrant, D.S. (2007). Evolution of Reproductive Seasonality in Bears. Mammal Review, 37(1), 21-53.

26. Struzik, E. (2006). Grizzly Bears on Ice. Retrieved July 21, 2015, from https://www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/2006/Grizzly-Bears-on-Ice.aspx

27. The Ecological Role of Coyotes, Bears, Mountain Lions, and Wolves. (n.d.). Retrieved July 21, 2015, from http://www.predatordefense.org/docs/ecological_role_species.pdf

28. The Wildlife Team, Denali National Park and Preserve (2003). Bear-Human Conflict Management Plan. Center for Resources Science and Learning

29. Tips for Coexistence with Black Bears – Western Wildlife Outreach. (n.d.). Retrieved July 21, 2015, from http://westernwildlife.org/black-bear-outreach-project/tips-for-coexistence-with-black-bears/

30. Trafficking of Bear Parts. (2008). Retrieved July 21, 2015, from http://www.bigwildlife.org/trafficking.php

31. Unger, D.E., Cox, J.J., Harris, H.B., Larkin, J.L., Augustine, B., Dobey, S., Guthrie, J.M., Hast, J.T., Jensen, R., Murphy, S., Plaxico, J., Maehr, D.S. (2013). History and Current Status of the Black Bear in Kentucky. Northeastern Naturalist 20(2): 289-308.

32. United States National Park Service. (2015, July 20). Denning and Hibernation Behavior. Retrieved July 21, 2015, from http://www.nps.gov/yell/learn/nature/denning.htm

33. U.S. Bear Gallbladders Sold on Black Market. (2010). Retrieved July 22, 2015, from http://news.nationalgeographic.com/news/2009/08/090811-bear-parts-trade_2.html

34. What are Keystone Species? (n.d.). Retrieved July 21, 2015, from http://www.keystoneconservation.us/keystone_conservation/keystone-species.html

35. Young, S., Jackson, H. (1978). The Clever Coyote. Lincoln: University of Nebraska Press

Written by Nicholas Franz

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Above photo: Grizzly bear in Alaska by Martha de Jong-Lantink via Flickr Creative Commons

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