SUPERIOR, Wis. — Finding a bear den randomly in the woods is tough, even if you know what you are looking for.
Bears use a hodgepodge of different shelters for dens — everything from the space under uprooted trees and hollows in the ground to piles of sticks or a few downed trees and even culverts.
When it's time for bears to take their winter naps, usually by late October or early November, they don't seem to be very picky where they set up shop. And once they're in the den they don't often come out to be seen or leave tracks in the snow.
That's why Wisconsin Department of Natural Resources bear biologists need your help. If you know the whereabouts of an active bear den in the Badger state, the DNR wants to hear from you.
This is the second winter of the DNR's "Black Bear Litter and Diet Survey" that is going into dens to find mama bears to discover how often they have cubs and how many they have. The goal is to come up with more accurate reproductive rates for black bears in each of the state's five bear management areas.
Researchers work in the winter, when bears have settled down in one spot, so they can find them, weigh and measure them and fit the sows with transmitter collars so they can be found again. (The females are tranquilized during the den visit so they don't pose any danger to themselves or the researchers.)
"Bears are really hard to count," said Randy Johnson, the DNR's large-carnivore specialist. "And the DNR isn't getting any bigger staff-wise. ... So any time we can get people to help us out, it helps. This is one of the cases where we really need people to help."
The data will help improve the accuracy of the population models used in each zone. It's those models that are used to set bear hunting permit quotas.
Last winter, the first for the DNR bear study, researchers managed to get collars on 13 female or sow bears at different dens reported by the public, from Iron County in the north to Jackson County in the south. This year they're hoping to double that number, said Jennifer Price Tack, lead researcher on the bear project.
Eventually researchers hope to have 100 female bears collared, 20 in each of the five management zones, and then follow them and their cubs for several years.
How often sows have cubs, how many cubs she has and how many of those cubs survive in large part determines which direction the bear population trends. Most often bears have one to three cubs, but it can be as many as four or more, or no cubs at all, depending on diet and other factors, Price Tack noted.
Under ideal conditions female bears produce cubs every other year. But one study showed that nearly 40% of sows did not breed for two straight years,
"There's still quite a bit we don't know about bears in Wisconsin, especially how much variation there is (on litter size and frequency) within the state," Price Tack noted.
Black bears are a big deal in Wisconsin, for the general public to see and for hunters to pursue. DNR public opinion polls show bears are widely loved by the public, even among people who have had bear problems like raided garbage cans, Johnson noted. The state has an estimated 26,000 bears, up from an estimated 8,000 back in 1989. And bears continue to expand their range southward.
The DNR is working to keep the bear population mostly steady across much of the state's bear range, although in Bear Management Zone D, wildlife managers are trying to reduce the bear population due to chronic issues of bears raiding farmer's fields.
This year hunters killed 4,110 bears, up from 3,847 in 2021. The harvest has been pretty consistent, averaging 4,100 bears killed each year. Bear permits are popular and at a premium. More than 135,000 hunters applied for about 12,000 bear harvest permits. (Depending on the zone, hunters must wait between 2 and 12 years to be drawn for a bear permit in the preference point-based lottery.)
Hunters also play a critical role in bear management by providing biological data from harvested bears, such as teeth. That data from hunters allows the DNR to determine the age and sex of each bear harvested and is the basis for the bear population modeling, Johnson noted.
This winter researchers will be working with landowners to visit dens, first determining if the den is safe, accessible and in use. They avoid dens that might be too close to roads or other possible human encounters that could end up badly for the sleepy bears.
The first goal is for the safety of the crew and the bears, and each bear is handled as little as possible.
Getting tracking collars on the sows and revisiting them each year will help staff determine the reproductive success of each sow, such as her litter frequency, litter size and the survival rates of the cubs. Data on sow weight, body measurements and age also is collected.
At the den, DNR staff monitor the sow's breathing and heart rate while the rest of the team quickly gather the needed samples and measurements. Any cubs present at the den are carefully weighed and sexed. Cubs are tucked into staff's coats to keep them warm because the cubs cannot yet regulate their own body temperature. Once researchers are finished, the sow and cubs are tucked back into their den.
"It's been really fun to get to know landowners who have bear dens and seeing how interested they are in their bears," Price Tack noted. "We try to keep them updated on what's going on with their dens and the bears that use them."
Researchers for the DNR and University of Wisconsin, Madison, also are investigating a connection between consumption of human food sources and bear reproduction because diet can affect cub survival rates and litter sizes. One past study in Iron County found that many bears are getting much of their food from human sources — be it garbage, bird seed, deer feed, gardens, agricultural crops, orchards or bait placed by hunters intended to attract bears into range.
In the past, how much natural food was available — acorns, berries, etc. — was considered critical in deciding how old females were when they had cubs, how often they had cubs and how many cubs they had. But now it appears that a high proportion of many black bear's diets in northern Wisconsin is composed of supplemental food from humans. That raises the possibility that supplemental food may be decoupling annual black bear reproductive measures from variation in the abundance of natural foods.
Indeed, the DNR says that observations of large litters of four and five cubs each — signaling very well fed female bears — seem to be increasing in Wisconsin.
The diet study will look at hair samples from bears collected across the state. DNA from the food sources leaves an isotopic DNA in the hair that can be sorted out in the lab. Scientists also will look at bear tooth samples submitted by hunters each fall to check for diet history.
"The isotopic information is in the teeth, too," Price Tack said.
Funding for the bear project comes in part from federal sporting goods sales tax money, so called Pittman-Roberstson funds, doled-out to state resource agencies.
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If you know where an active bear den is located, the Wisconsin DNR wants your help. Please report as much information about the den as possible while keeping your distance so as not to disturb the animal. Den locations from prior years can be useful since black bears will occasionally reuse dens. Go to surveymonkey.com/r/7DSMFZS to make your report.
— Size: A few black bear males can get really big, more than 500 pounds in some cases. But the average size is just 150 pounds for adult females and 300 pounds for males.
— Average age of a hunter-shot bear in Wisconsin: 4 years for sows, 3 years for boars.
— Breeding: Generally takes place from mid-June through mid-July. But female bears don't become pregnant right away. Instead, the fertilized egg does not implant in the uterus and begin development until the female enters the den for the winter. That's when, if foraging was good, she's at her peak weight.
— Cubs are born: In mid-winter while the mother is in the den, though pregnant females who are unable to gain sufficient weight prior to denning may fail to successfully produce a litter.
— Litter size: Black bears range from one to six cubs. In Wisconsin, the average is 2.7.
