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Ecology

“The Ecology of Two Black Bear Populations in the Interior Highlands of Arkansas” Joe Clark – 1990

By Clay Newcomb

Introduction

Since the inception of the first Arkansas bear season in 1980, the University of Arkansas has been funded to do numerous research projects about various issues pertaining to bear in the state. The first major study was conducted by doctoral student Joseph Clark and supervised by Dr. Kimberly Smith.  The study was was started in 1988 and went through1990 and was primarily designed to give insight into two areas: population dynamics and habitat usage of bears in the interior highlands of Arkansas. 

The study was divided into two areas. The first in the Ozarks at White Rock WMA in northern Franklin county.  The second in the Ouachitas in the Dry Creek area in Logan, Scott and Yell Counties. Arkansas bear populations are considered allopatric. This means the Ozarks and Ouachita populations are considered entirely separate, thus the need for two separate study areas. The two regions are separated by interstate 40 and the Arkansas River and bears typically don’t cross either. The thesis study was entitled “Ecology of Two Black Bear Populations in the Interior Highlands of Arkansas”.

The Arkansas Game and Fish had previously estimated bear populations but needed a more concrete understanding of bear numbers in the state.  This information would give them solid data to build an appropriately bear management plan.  Between 1980 and 1990 bear harvest numbers were relatively low, typically yielding between 5 and 31 bear harvests per year. Of the the bears harvested, a large percentage of them were under 3 years old.  Harvests that yield high percentages of young animals can mean one of two things. It could mean that bears were being over harvested and their were only young animals left in the population. Secondly, it could mean that because of high biological success of bears, the population was rapidly increasing and there was a high percentage of young offspring.  The population dynamic sector of the study was designed to answer these questions for the AGFC.  Was our bear population being over harvested and struggling? Was the population rapidly increasing?  The question needed to be answered and Joseph Clark and Dr. Smith set out to find the answer. 

The second question the study was designed to answer had to do with habitat usage.  There were many unanswered questions about habitat issues that needed to be understood in order to properly conserve and manage bear in the state.  How big are the home ranges of Arkansas bear? Do the ranges overlap?  Where do bears spend most their time during different parts of the year? What type of vegetation cover do they prefer?  What elevations are primarily used by bear in these mountainous regions? How do roads affect habitat usage?

During the study, 117 bears were trapped between the two study areas and many of the females were fitted with radio collars.  The collared bears were monitored in their daily movements, season home range travels and in their den sites.

Summary of Study Results

Population Dynamics

You can’t understand bear populations unless you have an understanding of bear reproduction.  Female bears, sows, typically reach sexual maturity between the age of 3.5 to 5.5 years old.  Sows give birth to cubs in their January den and nurse the cubs in the den until mid to late April. Sows can have one to four cubs per litter.  The cubs stay with their mother through the year and den with her the following winter.  Upon emergence from the second den, the yearling cubs become independent of their mother sometime during their second summer.  During this cycle, sows are typically bred every two years.  If a sow loses here cubs through mortality in the first year, which often happens, she will almost immediately come into estrous and be bred again. 

Bear reproduction is an amazing biological feat and is highlighted by what is called ‘delayed implantation’.  This is a process in which sows are bred in mid summer (June and July) but the egg is not fertilized until early winter.  The bear stores the unfertilized egg and the male sperm until conception timing is perfect for an early January birth. This process makes for a short gestation period and bears are born hairless and weigh less than one pound.  Because of small litter sizes and duration between litters, bears have the lowest reproduction rate of any large mammal in North America.  Most animals take one season to raise young but the bear takes two seasons.

The study found that Arkansas female bears exhibited young ages of sexual maturity, 66% of 2 year old females were bred and gave birth at 3 years old. Dry Creek bears had much higher litter sizes than the White Rock bears.  Sows also were noted to come into estrous earlier (mid May) than sows in other regions of North America.  As well, Dry Creek bear cubs had some of the highest survivor rates of any studies in North America at the time.  18 of 20 cubs re-denned with their mothers as yearlings during the study.  In White Rock, only 4 of 13 cubs re-denned with their mothers their second winter. Not denning with mother implies that the cubs died. One sow was found in the den with two newborn cubs and a 50 lb yearling.  This finding implied that the cub was lost during the summer and the sow came back into estrous and was bred.  The cub reunited its mother after she was bred and denned with her and the newborn cubs that winter.  Yearling cubs had some of the highest comparable weights of any bears in North America. 

Nutrition is a major factor affecting black bear reproduction.  When sows go into the winter den in poor nutritional shape they will not conceive and their bodies will absorb the unfertilized egg.  However, this study concluded that mast crop production as related to nutrition didn’t affect the reproductive success of bears in Arkansas.  Even in years with poor mast, the bears went into the dens in good nutritional shape. Excellent habitat in the study areas provided nutrition for the bears even in years with slim mast crops.

Another factor potentially affecting cub survivorship is cannibalism by males.  This ‘self-regulation’ action in carnivores is typically seen in population where food is abundant and the population is dense.  It is a natural population regulator.  Potentially, the poor cub survivorship in White Rock was due to a relatively dense population, though not much evidence of cannibalism was found.  This self regulation often causes sows with young to retreat to the areas with poorer habitat conditions to avoid male bears when the cubs are vulnerable.

Population Conclusions in 1990

Through bait station surveys and various methods Clark concluded that approximately 2,589 bears existed in the highlands of Arkansas.  Of that number 2,130 bears lived in the Ozarks and 480 in the Ouachitas.  On Dry Creek the populations had the highest density of the study areas with approximately 1 bear per 2.6 square miles.  White Rock was estimated to have 1 bear per 3.6 square miles. From the initial release of 254 bears the population had increased 10 fold since the 1950’s and 60’s.

Clarks report to the AGFC was that the population could handle a greater harvest than was currently being taken.  A population of bears can be maintained if the annual harvest doesn’t exceed 10%.  Clark concluded that the highlands could handle a harvest of roughly 200 individuals.

Habitat Usage and Home Range

Habitat usage was determined by monitoring radio collared animals and computing their locations with topographic maps and vegetation maps.  Clark and Smith were then able to determine the elevation, slope and vegetation cover of the area being used by the bears.  They collected hundreds of individual data points to produce what they call a ‘Habitat Model’. As well, throughout the data collection of the whereabouts of individual bears they were able to better understand home ranges of Arkansas’ bears as well as their primary movement times during the day.  Clark stated that food isn’t the only thing that drives bear habitat usage.  Things such as breeding, caring for young, obtaining water, avoiding extreme temperatures, resting and traveling are factors as well.

Home Range

The average home range for males was 57 square miles and 30 square miles for females.  Male bears have larger home ranges than females. This is primarily a sexually driven phenomena. Males must cover more ground to find potential mates.  Home ranges of Arkansas bears were relatively large as compared to other North American studies.  The summer ranges of bears were larger than fall ranges.  In summer bears cover more ground in search of summer mast.  In the fall mast in the form of acorns, hickory nuts and beech nuts are typically concentrated and caused bears to travel less in the fall. 

Bears are diurnal, which means their natural movement patterns are during the daytime.  Clark found that bears were most active between 8:00 am and 10:00 pm at night (take into consideration that in summer it is daylight until 9:00 pm). 

Home ranges of bears overlapped significantly.  Females were more likely to maintain the exclusive use certain portions of their range during certain times of the year, particularly summer.  Females were found to mutually avoid each other, especially while raising young.  This finding concludes that females, though their home ranges overlap, are territorial.

Habitat Usage

Clearcuts

Their were some clear patterns of habitat preferences found during the study.  ‘Clear cut’ or ‘regeneration’ areas are key for summer production of soft mast.  Though much bear sign was seen in these areas, the radio collared females used these areas less than expected. Clark concluded that it may have been because the males used these best food producing areas causing the females with young to avoid them.  As well, it was concluded that bears feel more vulnerable in the open areas and didn’t use them as much, even though the food was abundant.  Areas with good sized trees, which are used as potential retreat sites, make for good areas for sows and cubs to feed.  Often times the clear cuts didn’t provide this.  Clark concluded that efforts to increase cover in clear cut areas would be beneficial.  The inclusion of stream buffer strips, islands of standing timber, irregular boundaries and reduction in overall size would would increase their value to bears.

Big Timber and Elevation

The Ouachita bears during the summer primarily stayed in areas with good blueberry production. The berries often occur as understory plants in the mature hardwood timber. The Ozarks have less blueberries and the bears targeted other types of soft mast (pokeweed, cherry, downy serviceberry, carolina buckthorn and blackgum). Overall, in both study areas bear typically avoided areas of big pine timber. Mature pine timber has little value to bears other than cover, and any soft mast producing species that grow beneath them.  As would be expected, habitat usage in the fall revolved around acorn production in both study areas.  In the fall bears were more concentrated on east facing slopes. These slopes typically have more consistent fall hard mast.

The highest usage and habitat association for bears occurred on north facing areas with mature hardwood timber.  These areas typically have large numbers of white oaks and black gum and are associated with high soil moisture and organic matter content.  Understory plants growing in such an area would be black walnut, spice bush, may apple and basswood (among others). Areas like this are critical for bears and should be preserved.

In this study, bears typically preferred middle elevations on the mountains, as opposed the ridge tops and the valleys.  This doesn’t mean that they don’t use these other areas, but they spent more time in the middle elevations.  As well, the Ouachita bears showed a consistent avoidance of south facing slopes during all times of the year. 

Roads

In both study areas bears showed a strong avoidance towards roads, especially during the fall.  This is likely due to increased hunting traffic in the fall coinciding with deer season.  Bears primarily avoided roads that were used more frequently by humans.  The smaller roads and trails were avoided less.

Interesting Findings

  • Bears in the interior highlands of Arkansas were found to be relatively large as compared to other regions because of food-rich habitats of the area.

  • Ozark bears are 25% color phase (brown).  Ouachita bears were found to be roughly 3% color phase.  Brown and black were the only colors of bears in Arkansas.  This is interesting because of the bears released during the reintroduction few were documented as brown.  The area in Minnesota where the bears were trapped was only 3% color phase.  Typically, the percentage of non-black bears increases as forrest canopy opens up. 

  • Ouachita bears make their living off large amounts of summer blueberries.  Ozark bears capitalize on large areas of mature hardwood timber that produces excellent fall mast in the form of acorns, hickory nuts and beech nuts.

  • The oldest bear that Clark and Smith caught was a 26 year old male that weighed 235lbs.  Bears can live up to 30 years in the wild.  Bears are aged by slicing a section of a tooth and counting the cementum annuli rings. 

  • A total of 48 bears were captured on White Rock during a three year period. On Dry Creek 69 bears were captured during the same period.

  • The best habitats on Dry Creek supported slightly higher densities than on White Rock.

  • During the study one female bear was killed by lightning during a summer thunderstorm.  One 3 year old male was killed by vehicle on Interstate 40 near Sallisaw Oklahoma. It was originally trapped 176 miles away in the White Rock study area.

  • The average litter size for both areas combined was 1.86 cubs per litter.  Dry Creek litters were typically larger.