THE LARGEST LIVING TERRESTRIAL CARNIVORES
ECOLOGY OF THE AMERICAN BLACK BEAR (URSUS AMERICANUS) AND GRIZZLY BEAR (URSUS ARCTOS)
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.
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).
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).
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).
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)
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.).
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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Written by Nicholas Franz