Profileof the Black Bear in the Chihuahua Desert
Profileof the Black Bear in the Chihuahua Desert
Introductionto the History of the Chihuahuan Desert
TheChihuahuan Desert is the largest desert in North America occupying175,000 square miles. It is usually called the rain shadow desertowing to the two vast mountain ranges on the East the Sierra MadreOriental and the Sierra Madre Occidental on West (Morafka, 1977). Thedesert developed because the two mountains blocks moisture from thePacific Ocean and the Gulf of Mexico from reaching the land. Most ofthe deserts’ location is in Coahuila in Mexico and states ofChihuahua, but it extends and reaches up into Southern New Mexico,Texas, and Western Arizona. On the other side, it extends down to SanLuis Potosi in Mexico and states of Zacatecas (Morafka, 1977). It hasnumerous small mountain ranges, which extend through it includingDona Anas and San Andres in New Mexico and Franklins in Texas makingthem some of the most significant characteristics of the ChihuahuanDesert. Although the desert has minimal rainfall, the small streams,underground springs, and the Rio Grande River provide precious waterrequired for the survival of plants and animals in the area (Onoratoet al., 2004).Therefore, the Chihuahua has a large riparian region, which meansthat diverse species of plants and deserts can survive within itsboundaries, one of these animals being the black bears, UrsusAmericanus(Lariviere, 2001).
BlackBears Habitat in the Chihuahuan Desert
Blackbears are considered natural forest creatures, but they also live inother habitats as long they can find food. The black bear was once aspecies distinguished by its widespread distribution throughout theMexican side of the Chihuahuan Desert. The black bears are extremelyadaptable to forested surroundings living in both arid and forestsareas located at regions in the sea level to approximately 6,560feet, which makes the Chihuahuan Desert a favorable habitat(Ahlstrom, Schroeder & Baker Street Productions, 1985).Historically, the black bears live in all forested habitats in theChihuahuan Desert, but they are widespread to the Chihuahuan Desert’ssky island. Additionally, they lived in temperate forests SierraMadre Oriental, Occidental, and adjacent mountains in the ChihuahuanDesert (Murray, 2005). The black bears have resided in the NorthAmerican region for approximately three million years. In the WesternTexas side of the Chihuahuan Desert, they are found in the lowerdesert elevation and pine-oak woodlands of the mountains (Ahlstrom,Schroeder & Baker Street Productions, 1985). Their dens in theregion vary depending on the seasons, locale, and conditions. Duringwinter, the fallen trees, brush piles, cave bottom of tree roots andbrush piles are perfect dens for the bear.
However,they prefer the higher and more isolated areas within the ChihuahuanDesert as compared to the desert’s floor. Thus, they like theregion of Trans-Pecos Western Texas because the area mainly consistsof grassland and shrubs with patches of higher elevation between 1500meters and 2000 meters (Ahlstrom, Schroeder & Baker StreetProductions, 1985). The black bears can be seen at any time of theday, but they are very active during the night. Nonetheless, it isbelieved that the black bear were eradicated from the Trans-Pecosregion due to overexploitation by human activities, but theirpopulation survived in the South in the mountains of Northern Mexico(Hellgren,Vaughn & Stauffer, 1991).The West Texas side of Chihuahua forest has a variety of vegetationand cover at higher elevations of the mountains, which makes theregion favorable for the black bears. In the Southeastern side of thedesert, the black bears occupy approximately 20 percent of theirhistorical habitats in the ranges (Powell, Zimmerman & Seaman,1996). However, the black bear populations are hard to monitor andrecord because they live in relatively low densities and are verysecretive (Ahlstrom, Schroeder & Baker Street Productions, 1985).The contemporary population of black bears is unevenly distributedand isolated throughout Mexico and the United States region, but theestimates range from 600,000 to 800,000, and currently increasing(Lariviere, 2001).
BlackBear’s Feeding Habits
Theblack bears are omnivorous as they feed on a broad range of foodsdepending on its availability. The black bears diet comprises of 75percent vegetables, 15 percent dead animals’ decaying flesh, and 10percent small mammals and insects (Fergus & Hansen, 2005). At thehigher elevations of the desert, the black bears feed on madrone,acorns, algerita, juniper berries, pinyon nuts, Mexican squawroot, avariety of insects, grasses, and carrion (Onoratoet al., 2004).On the other hand, they mainly feed on prickly pear fruits, Texaspersimmons, grasses, Spanish dagger, mesquite beans, acorns yuccahears and sotol in the lower desert elevations. The black bears spendmost of their time searching for food. A majority of their dietconsist of green vegetation during the springs and mainly variousnuts and berries during the summer. Alternatively, they feed onsweet, ripe corn, and honey especially during the winters (Fergus &Hansen, 2005).
BlackBear’s Physiologicaland physical characteristics
Theblack bear is a medium-sized animal with a brown muzzle and often awhite patch on the chest. They have a broad head with a long thinmuzzle, but the females have a smaller and long-pointed head ascompared to the males. Although black is the dominant color, some ofthese bears have others colors such as cinnamon, blonde, chocolatebrown, or even reddish (Halvorson, Schwalbe & Van, 2010). Theyhave long and coarse guard hairs while the underfur is dense and softto provide proper insulation. The black bears have a massive bodystructure with huge shoulders thick legs and a short back to give itpower and strength. An adult black bear’s length from the paw tothe shoulder is between two and a half and three feet tall, and fourto six feet long from the tail to the nose (Kolpin, 2012).
Ablack bear has 42 teeth with the adult teeth developing once the bearreaches two and a half years (Onoratoet al., 2004).Accordingly, it is possible to determine the bear’s age byanalyzing the cement deposits around a premolar tooth. Their longcurved claws help them climb tree trunks to reach leaves, nuts,seeds, as well as ripping open mounds and logs searching for insects.The black bears have five toes, and they walk using the whole sole oftheir foot, which are dark and deeply wrinkled. The bear’s trackscan be used to indicate its sex, weight, and age. An adult male blackbear forefoot track is four inches wide by four and a half incheslong and the hind foot measures four inches wide by seven incheslong. Additionally, the bears have detached lips, which make it easyfor them to pluck berries from trees and shrubs (Hellgren, Skiles &Onorato, 2005).
Onthe other hand, the weight range for an adult black bear depends onthe diet, sex, and the region it resides within the ChihuahuanDesert. The males are up to 33 percent heavier than the females,which weigh between averages of 100 to 400 pounds (Kolpin, 2012).However, the black bears on the Eastern side of the Chihuahuan Desertare larger as compared to those residing in the in the Western regiondue to the vast availability of food. The black bears have excellentlong-term memory, which helps them in recalling an area within thedesert where they can find food or the way home in the long rangesaround the wilderness. Although a bear can run swiftly over a shortdistance and even reach up to thirty miles per hour, they cannot runfor long distances because their bodies overheat very quickly owingto the large size. Research suggests that bears have a remarkablesense of smell, which helps them to locate mates, detect and avoiddanger, and to find food. Although the black bear is seemingly clumsyand large, it is extremely skillful, which means it can handle smallobjects (Hellgren, Skiles & Onorato, 2005).
Thenagain, the black bears have unique physiology that helps them survivein the Chihuahuan region. The bear’s digestive systems lack therumen and cecum, which are found in other herbivorous. Consequently,the food moves quickly through their digestive systems thus, much ofthe plant fiber is undigested especially before they go intohibernation (Hellgren,1998).Nevertheless, they produce ursodeoxycholic acid that they store inthe gallbladders, which prevents gallstones, improves digestionduring the winter, and enable them to lose fat, but gain muscle(Powell, Zimmerman & Seaman, 1996). Besides, the bear’s bodysolves the problem of food moves quickly through their digestivesystems by eating vast quantities of food before they hibernate. Theyalso selectively search for plants that are easily digestible andmainly concentrated with nutrients such as nuts and fruits (Hellgren,Skiles & Onorato, 2005).
Themetabolic changes in the black bears make them hibernate for up toseven and a half months without drinking, eating, urinating, ordefecating (Hellgren,1998).However, the black bears cannot be considered as genuine hibernatorsbecause they lower their body temperatures by approximately 10percent while slightly decreasing heart rates and breathing. Duringhibernation, they use fat reserves gained during fall and summer forenergy while the urea found in urine is reprocessed back into thebody to manufacture muscle tissue (Murray, 2005). Thus, a bear cangain muscle mass even if it may ultimately lose between 20 and 40percent of the weight. Nevertheless, their hibernation behaviors arenot universal because the bears in the South of the desert do nothibernate because the food is available throughout the year exceptfor the pregnant females (Hellgren,1998).
Thefemale black bears produce the first cubs at the age of three toseven but stop reproducing when they reach their mid-20s depending onthe diet. The males attain sexual maturity at the age of betweenthree and five years (Hellgren,Vaughn & Stauffer, 1991).During the seven and a half months hibernation, a female black beargives birth to two or three cubs and in some rare cases up to six.However, the bears mate during the mid-summer but the embryos do notattach to the uterine wall immediately after fertilization. The cubsare born in January with their eyes open unlike in some otheranimals, and they become active between five and six weeks (Maehr,Noss & Larkin, 2001). During the spring, the bears leave the denwith the cubs weigh between four to eight pounds, but quick gainweight to a maximum of 75 kilograms by mid-summer. Nonetheless, theweight gain and size increase depends on the availability of food inthe desert. Thus, it makes the bears on the Eastern side susceptibleto reproduction decrease when the vegetation species are lessproductive due to their larger size (Onoratoet al., 2004).
ThreatsFacing the Black Bears
However,the Chihuahuan Desert has been through several changes throughout itshistory and especially in the past one and half century. The grass inthe Northern region of the desert grew very high in the 1850s, butsince then, desertification has been occurring at a very quick pace(Maehr, Noss & Larkin, 2001). Consequently, the areas in thedesert that were once desert plains are currently shrub desert withlittle grass, which instead is affecting all desert life includingthe black bears. Besides, the loss of riparian habitats and minimalwater supply has also affected the population of black bears in thedesert (Onoratoet al., 2004).
Furthermore,the black bears were considered a barrier to human development andsafety in the area during the 20thcentury. Therefore, this viewpoint as well as habitat destruction,fragmentation, and unrestricted hunting of bears led to a decrease ofthe black bear population especially in the Southern side of theChihuahuan Desert (Halvorson, Schwalbe & Van, 2010). Besides, theillegal trade in bear parts such as the gall bladder, ursodeoxycholicacid, and fur has raised concerns about the effects of poaching onthe bear population. Fortunately, some black bears remained in theChihuahua Mountains, which provided a source for naturalre-occupation in the region.
Nonetheless,there is a possibility the black bear population will recover if thenecessary preservation tactics are implemented. Currently, the blackbears have reentered the parts of their former habitats in theTrans-Pecos region of the Chihuahua after an absence of more thanforty years (Hewitt & Fulbright, 2007). Presently, the World WideFund for Nature (WWF) has implemented several strategies to conservethe Northern Chihuahuan Desert and the regions of Rio Grande Bravowatershed in Mexico and the United States to improve the animals’survival chances (Cartron, Ceballos & Felger, 2005). For morethan fifteen years now, the WWF and the bi-national partners havebeen operating in the Northern Chihuahuan Desert to preserve andbring back grassland ecosystems and back freshwater for the benefitof people and most importantly the wildlife (Hewitt & Fulbright,2007). Moreover, these initiatives are also changing the publicattitude towards the bear, which has significantly contributed to therecuperation and increase of the bear population in the region.
TheChihuahuan Desert covers one of the most biologically diverse aridareas on earth. The eco-region extends from within Mexico into theUnited States with two vast mountain ranges, which contributes to itssignificant features. The Chihuahuan Desert is unique as it isprotected from the influence of other arid regions, which allowed theevolution of many endemic species such as the American black bears.The black bears are one of the dominant species in the area due to itmountain elevation, availability of food, and water. Although theyfeed on proximity to each other, the black bears are solitary animalsexcept for the females with cubs. The black bears prefer to live inhigh elevation within the desert as compared to the surroundingenvironment on the floor of the Chihuahuan Desert. The bear’sphysiology and physical characteristics make it possible for theanimal to survive in the region. The black bears usually have fewenemies in the jungle, but they fear the grizzly bears the most. Inthe wild of the Chihuahuan Desert, a black bear can survive between21 to 33 years. However, the bear population is endangered by arising human population, mismanagement, water misuse, overgrazing bygoats and cattle and lack of information about the desert’secological significance. Luckily, it is possible to mitigate theseproblems using management and education plans based on comprehensivescientific knowledge of the Chihuahuan region and the black bears’characteristics to help save these fascinating animals.
Ahlstrom,M. E., Schroeder, H., & Baker Street Productions. (1985). TheBlack Bear.Mankato, Minn: Crestwood House.
Cartron,J.-L. E., Ceballos, G., & Felger, R. S. (2005). Biodiversity,Ecosystems, and Conservation in Northern Mexico.New York: Oxford University Press.
Fergus,C., & Hansen, A. (2005). Bears.Mechanicsburg, PA: Stackpole Books.
Halvorson,W. L., Schwalbe, C. R., & Van, R. C. (2010). SouthwesternDesert Resources.Tucson, AZ: University of Arizona Press.
Hellgren,E. C., Skiles, J. R., & Onorato, D. P. (2005). Dynamics of aBlack Bear Population within a Desert Metapopulation. BiologicalConservation,122(1), 1-29.
Hellgren,E. C., Vaughn, M. R., & Stauffer, D. F. (1991). Macrohabitat Useby Black Bears in a Southeastern Wetland. Journalof Wildlife Management,55, 442–448.
Hellgren,E. C. (1998). Physiology of Hibernation in Bears. Ursus,10,467–477.
Hewitt,D. G. & Fulbright, T. E. (2007). WildlifeScience: Linking Ecological Theory and Management Application.New York: CRC Press.
Kolpin,M. (2012). AmericanBlack Bears.Mankato, Minn: Capstone Press.
Lariviere,S. (2001). Ursus Americanus. MammalianSpecies,647, 1-11.
Maehr,D. S., Noss, R. F., & Larkin, J. L. (2001). (Ed.). LargeMammal Restoration: Ecological and Sociological Challenges in the21st Century.Washington, DC: Island Press.
Morafka,D. J. (1977). ABiogeographical Analysis of the Chihuahuan Desert through itsHerpetofauna.Dordrecht: Springer Netherlands.
Murray,J. (2005). Blackbears.Edina, Minn: Abdo Pub.
Onorato,D. P., Doan-Crider, D. L., Hellgren, E. C., & DenBussche,R, A. (2004). Phylogeographic Patterns within a Metapopulation ofBlack Bears (Ursus americanus) in the American Southwest. Journalof Mammalogy,85(1), 140-147.
Powell,R. A., Zimmerman, J. W., & Seaman, D. E. (1996). Ecologyand Behaviour of North American Black Bears: Home Ranges, Habitat andSocial Organization.London: Chapman & Hall.