Bear facts
Camp Ripley study could help humans
Although one of the larger animals in the woods, bears seldom are seen. If they didn't wander into people's backyards in search of food many of us would never see a bear in a natural setting.
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How can an animal whose adult weight averages 400 pounds be so secretive?
It's an anomaly of the bear, and there are others. How, for example, does a bear maintain its muscle mass during hibernation, when it doesn't eat for several months? How can a bear's body heal during hibernation, when its pulse rate is low? Researchers have found newly denned bears with huge scars, then returned in the spring and found the scars have healed.
Answers to these questions might be useful to humans. People who are bed-ridden or physically inactive for long periods of time could benefit from knowing how an immobile bear retains its muscle mass and heals itself.
A black bear is collared at Camp Ripley as part of an ongoing study to try to learn more about the elusive animals. Currently, six bears with GPS collars are being monitored by researchers. Camp Ripley Environmental Staff
Since 1991 Camp Ripley, the Grand Rapids area and Voyageurs National Park have been the sites of a bear study that one day might help answer these questions. Camp Ripley got involved when nuisance bears started rummaging around in bivouac areas. When the troops made garbage pickup a daily chore the problems ceased. Today the Camp Ripley study aims to learn more about bears' reproductive rates, movements and mortality.
Unlike deer and wolves, bears can't be rounded up for study purposes with the aid of an airplane. They must be trapped, and to that end 13 traps have been set for bears throughout the 52,000-acre military reservation. Traps are cylindrical drums with an opening at one end. A chunk of bacon is placed at the back of the drum. When a bear enters the drum to get at the bacon a trap door is triggered. Trapped bears are outfitted with GPS collars, allowing researchers to track their movements.
Traps are checked daily. More skunks and raccoons are caught than bears. Critters that become too much of a nuisance are caged and hauled away. Sometimes the trap itself must be moved to a new location.
On the morning of June 11, rain and wind swept over Camp Ripley as Brian Dirks, a member of the Camp Ripley Environmental Staff, checked traps. It wasn't the kind of weather in which larger, furry critters like to roam about, but Dirks was hopeful he could add a new bear to the current roster of six collared bears.
When a bear is captured in a trap, a tranquilizer must be applied with a jabstick before researchers can work on the bear. Cmp Ripley Environmental Staff
"We've trapped two so far this year," Dirks said. "One is a young, 2- to 3-year old female. The other is an adult male. We won't know the exact ages until we get the tooth aging data back."
Camp Ripley's permanent resident bear population is estimated at 15, but as many as 25 different bears wander on and off the reservation over the course of the year. Mortality rates are high. Nine bears collared last year already have died. Hunting and vehicle accidents are the leading cause of death. But two young bears died from unknown causes, puzzling the study team.
"There's a hundred possibilities," said Dirks, noting that bears are susceptible to diseases and maladies unknown. "They may have eaten something poisonous. We don't know if they're affected by West Nile or Lyme's Disease. It's all speculation."
The study has found that bears' reproductive rates are higher in the southern half of their range. Southern bears reach reproductive maturity at a younger age and deliver more cubs per litter. Availability of food is believed to make the difference. Acorns and black berries are two high-quality food sources not available to northern bears, nor do they have access to agricultural crops such as corn and soybeans.
Sometimes an unwanted critter gets in a bear trap, in this case a raccoon. If the critter becomes too persistent, it's moved several miles to prevent it from entering the trap again.
Female bears in Camp Ripley average three cubs per litter, while northern bears average two. And Camp Ripley bears have cubs every other year while a northern bear often skips two years between litters.
Rutting season for bears is now. Females deliver cubs in hibernation in January and nurse the cubs until they venture outside in spring. Bears never completely shut down in winter like squirrels do. A bear's body temperature and heart rate continues to fluctuate throughout the long winter days in the den.
Camp Ripley's bears hibernate from late October to early April, though they've been found to den as early as September and as late as December. Most den in holes in the ground, though some build above-ground dens.
"It looks like a big bird's nest and usually is tucked in against tree roots or a windfall," Dirks said. "Sometimes they're a foot or more deep. We found a female hibernating in a big brush pile. She had her cubs and must have just laid on them when it was 20 below. She had her next litter in a hole in the ground, then her next one in the brush pile again."
With GPS collars, researchers can pinpoint a bear's travel patterns over the year far better than conventional radio telemetry. The GPS collar gives a location every four hours. A radio-collared bear must be found with an airplane.
Brian Dirks, a member of the Camp Ripley Environmental Staff, checks a map showing the location of bear traps within the 52,000-acre military reservation. Traps are checked on a daily basis. Brainerd Dispatch/Vince Meyer
Male bears move farther and more often than females, which seldom wander more than a few miles off the reservation. Not so with the males. One adult male collared in Camp Ripley traveled the entire circumference of the 83-square mile reservation. In May it embarked on a long pilgrimage that took it as far north as Emily, where it summered. Then, not unlike the local human seasonal residents, it went south again when the air got cold, returning to Camp Ripley. It left again the following spring and was hit by a car in Jenkins.
Bears can be aged by their teeth. The molar grows rings, not unlike a tree. Teeth also reveal stress (growth ring not as wide), revealing how often the sow has had cubs. Collared bears near Grand Rapids were found to have lived more than 30 years.
On this morning none of the traps have a bear, though two raccoons have helped themselves to the bacon. Dirks released one coon on site while two other members of the study team, hauled another away and released it. The team was hopeful that the weekend would be more productive.
Two collared bears from the Camp Ripley study have been seen in Brainerd area. If you see a bear with a red collar, call the Camp Ripley environmental office at (320) 632-7635. To report a nuisance bear, contact the Brainerd area DNR wildlife office at 828-2314.
VINCE MEYER can be reached at vince.meyer@brainerddispatch.com or 855-5862.