1836 What Were Learning About Black Bears in - webapps8

What We're LearningAbout Black Bearsin MinnesotaBears in north-central Minnesota producemore robust cubs than those in northeasternMinnesota. Why is this so? Two DNR wildlifebiologists report on black bears they havestudied over the past three yearsKaren Noyce and Dave GarshelisPICKING OUR way through winterbrittlealder and squeakingsnow, we approached the den with acertain anticipation. Twenty feetfrom the mound of dirt marking theden entrance, we stopped. Last yearthis bear, female #400. was alert inher den, making it difficult to getclose enough to administer the immobilizingdrug. But last year shehad year-old cubs. This Decembershe should be pregnant with a newlitter. Based on previous experiencewith pregnant females, we expectedher to be soundly asleep.We were still 10 feet away whenwe heard the telltale pop-pop of herjaws and the heavy breathing characteristicof a not-too-pleased bear.There she was, head up, staring usstraight in the eye, and looking notthe least bit groggy from her eightweeks of rest. So much for ourtheory about pregnant females.It has taken three winters ol visitingbear dens to learn a simple lesson:Some bears sleep soundly,whereas others are more wary intheir dens, regardless of sex, age, orreproductive status. It will requiremany more years to answer importantquestions: How many cubs areborn each winter? How many surviveto adulthood? What factors influencerates of reproduction andAbove: In spotter plane, observer Karen Noyce locates radio-collared bearsby telemetry. Directional antenna is on wing strut at right. Left: Branchholds jaw of drug-immobilized bear open. (Color photo by Tim Smalley, DNR.)37

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Studying Black Bearssurvival? The answers will help uspractice responsible bear managementin Minnesota.Fortunately, many of the intricaciesof bear ecology in Minnesotahave already been revealed by U.S.Forest Service biologist Lynn Rogerswho studied bears for 15 years inthe Superior National Forest. Rogers'data have been helpful in establishingguidelines for managing Minnesota'sbear population, but growinghunting pressure through thelate 1970s made it apparent thatmore data were needed. Also, thereis a strong likelihood that populationparameters differ widely betweenRogers' study area on the CanadianShield and other parts of the state.Thus, the Department of NaturalResources initiated its own blackbear research project in late 1980 innorth-central Minnesota.females sometimes fail to produce alitter. Instead ol having cubs everyother year, it may be three or fouryears between litters. This may bedue to premature termination ofpregnancies when females enterdens in poor condition. In threeyears of our study, all adult femalesentered dens in relatively good conditionand produced a litter everyother year. In addition, females innorth-central Minnesota are largerthan females in the northeast andproduce more robust cubs.What accounts for these differencesin reproduction between thenortheastern and north-central partsof the state is not known, but we suspectit is related to differences in thequality of food resources. Bears arePursuing Answers. With nearlythree years of field work completed,some important questions are beinganswered, but many mysteries stillremain.We found, for example, thatfemales in north-central Minnesotareach sexual maturity and breedduring June of their third or fourthyear, and occasionally when they areonly two years old. Conversely, Rogersfound that many females innortheastern Minnesota do notreach sexual maturity until five- oreven six-years of age and producetheir first litters at six and seven.Rogers also observed that adultTop, left: At bear's den, Noyce jabs bear with drug in syringe on end of pole.Bottom, left: Drawing blood from femoral vein of cub. Above: Noyce and coauthorDave Garshelis carry trap for mid-May to mid-July live-bear study.39

Studying Black BearsHow to weigh a bear? Noyce and Garshelis use a net, scale, and sturdy branchprimarily vegetarian. They live ongreens, catkins, carrion, and insectsuntil mid-July, then turn to wildfruits and nuts for the remainder ofsummer and fall.In most parts of the country, includingnortheastern Minnesota, insectslike ants and bees make up lessthan 15 percent of the volume ofbear droppings in any season. Wehave found, however, that betweenmid-June and mid-July, just beforeberries begin to ripen, ants dominatethe diet of bears in northcentralMinnesota, comprising65-75 percent of scat volume.It is possible, therefore, that thisconcentrated source of protein contributesto improved reproductivesuccess of bears in our area. In addition,oak trees, farm crops, and garbagedumps are more prevalent herethan in northeastern Minnesota, andthe longer growing season and richersoils of our area may provide morereliable wild fruits each year.Bear Deaths. Indirect evidencesuggests that some cubs die duringtheir first year. Cubs generally staywith their mother for a year and ahalf, but of 25 cubs checked in theirnatal dens, only 20 were re-observeddenning with their mothers the followingwinter.These youngsters are too small to40 THE MINNESOTA VOLUNTEER

What do bears eat? In laboratory, Noyce examines scats, finds tree seed, right.wear radio transmitters, so the fateof the five missing cubs is unknown.Some may have parted companywith their mothers earlier than usualand survived on their own. However,some of the missing cubs mayrepresent mortalities, especiallysince their siblings remained withthe mothers.Hunting accounts for the greatestnumber of adult bear deaths, sohunting pressure must be controlled.But what constitutes anacceptable level of hunting mortality?Theoretically, the harvestshould equal the number of newcubs born each year, minus thenumber of bears dying from causesother than hunting. Data from ourtelemetry study and from Rogers indicatethat hunting mortality shouldconstitute roughly 10-15 percent ofthe total bear population. Unfortunately,there is no easy way to estimatethe population of bears that inhabitdense forests.One way to estimate populationsize is to catch and radio-collar allbears in a given area. The bear densityobserved in that area can thenbe extrapolated to other areas ofsimilar habitat. Rogers collared everybear in his study area in northeasternMinnesota, and we havenearly accomplished this in our area.Surprisingly, bear-density estimatesMARCH-APRIL 1984 41

Studying Black BearsTop: Ken Kerr, DNR medical technologist,measures electrolytes in bear's blood.Bottom: Computer analyzes study data.cooperate by submitting teetli fromtheir bears which we use to determinethe animal's age. They alsoanswer survey questions about location.duration, and success of theirhunt so we can quantify huntingeffort.At present, our best estimate derivedfrom the computer model is apopulation of 6,000-7,000 bears inMinnesota. Unfortunately, the modelmakes a lot of assumptions aboutbears. Our estimates may change asfurther research shows us that someassumptions are incorrect.for these two areas are nearlyequivalent: one bear per two orthree square miles.We also are using a more theoreticalapproach to estimate the state'sbear population. Male bears, especiallyyoung males, are more vulnerablethan females to hunting. A computerprogram examines the maleto-femaleratio in each age-class ofbears in the harvest. These ratios,when compared to a measure ofhunting pressure — for example,hunter-days afield — exerted on thepopulation over several years, enablethe program to calculate thepercentage of the population representedby the legal harvest. HuntersWhy Nuisance Bears? The shootingof nuisance animals is the secondmost important cause of bear mortalityin Minnesota. A nuisance bearmay be anything from an individualthat wanders into town and raids afew garbage cans to one that causesconsiderable damage to crops, beehives,livestock, or other property.Nuisance bears are reported to localDNB Conservation Officers who usetheir discretion in handling eachcase. Some of these bears are killed,some are transported to other areas,and others leave on their own.Every year, Conservation Officerssend us a report summarizing eachcomplaint they investigate. In thisway, we monitor fluctuations in nuisance-bearactivity across the state.Numbers of complaints vary42 THE MINNESOTA VOLUNTEER

greatly from year to year, more thanwe can attribute to changes in thenumber of bears. Also, the peakperiod for nuisance activity differsamong years. For example, nuisanceactivity was high both in 1981 and1983. Most complaints in 1981 wereregistered in August during astatewide failure of many wild fruits.In 1983, most complaints occurredin June and early July, but taperedoff as a good crop of fruits ripened inAugust. This suggests that availabilityof natural food largely influencesnuisance behavior.The old adage proves true: Themore we learn, the more we need tolearn. It may seem a small lessonthat individual bears vary in theirbehavior, but the ramifications ofthis loom large. If all bears were thesame, our task would be easy. As itis, the individuality of these animalsadds enormously to the time andeffort necessary to uncover each axiomof bear biology. As scientistspracticing wildlife management, wesearch for commonalities, but as humanswe get secret enjoyment fromthe bear's unpredictability.When the time comes to countcubs in dens this spring, female#400 will undoubtedly make thatpoint clear once again. •Karen Noyce and Dave Garshelisare wildlife biologists specializing inblack bear research at the DNRForest Wildlife Population and ResearchGroup, Grand Rapids.&-frHow Many Turkey Hunters Are SuccessfulPDESPITE SNOW, cold, rain, and strong winds during most of last year s 25-daylongspring turkey hunt in Minnesota, more birds were harvested than in the1982 season. By May 8, the day the hunt ended, DNR checking stations recorded116 birds — a nine percent increase over 1982. About 1.700 huntersparticipated in the season; one hunter in 14 bagged a turkey.— DNR News ServiceCost of Water to Produce Food We Eat Each Year: $3,000"THE CURRENT, single, greatest consumption of water in the United States is foragriculture and the irrigation of crops for the production of food. Based upon theamount of water needed to grow the food products which we typically consume. . . the following prices would have to be added to cover the cost of the waterused in production. For a hamburger, French fries, and cola, $3. For a loaf ofbread, 60 cents. For a pound of beef, $8. For a dozen eggs, 96 cents. For abushel of corn, $10. At a price of two cents for every 10 gallons, it would cost$3,000 a year for the water to produce the food for just one person in the United— Journal of FreshwaterMARCH-APRIL 1984 43