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Say you were a deer living last week near Orr, Minn., about halfway between Duluth and International Falls. You've had a tough few days, weather-wise. Beginning Sunday, the temperature lows were minus-29, minus-29, minus-20, minus-20, minus-35 and, on Friday, minus-33.
Looking for relief in daytime? Forget it. High temperatures never rose into positive territory.
Yet it's unlikely many, if any, deer in the area died because of the frigid temperatures, in part because this most recent cold snap has been fairly short in duration and in part because deep snow hasn't been a problem: Only 6 inches or so is on the ground in Orr, according to the National Weather Service.
Thanks to their unique physiology and behavior adaptations, deer can survive such severe weather. Consider:
• Throughout summer and fall, deer increase their fat reserves, which are critical to winter survival. Fawns born in spring and early summer spend too much energy contributing to skeletal and muscle growth to add much fat, making them more susceptible to dying in winter than does or bucks. Bucks, meanwhile, endure risks because they expend so much energy during breeding season, and also forget to eat while chasing does. So they, too, are at higher winter survival risk.
• A deer's coats are engineered to help him or her endure extreme cold. Their guard hairs, which make up their outer coats, are long and hollow, allowing them to trap air, which acts as insulation. These hairs also shed water readily, thanks to a gland's oily secretions. Providing most of a deer's insulation, however, as any hunter learns when field-dressing a whitetail, is a thick mat of shorter, dense hairs that lie beneath the guard hairs.
• To survive cold weather, many deer will migrate to wintering areas typically dominated by conifers and ideally located near areas where browse, or food, can be obtained. Conifers offer warmth to deer lying beneath them, and because less snow reaches the ground in thick conifer stands, deer can more readily devise trails and escape routes in these areas than in deciduous tree stands. If available, nearby clearings give deer a chance to soak up sunshine in daytime. In northern Minnesota, such deer "yards" often hold many deer, which can increase an individual deer's chances of survival if wolves are present.
• Notwithstanding the migrations, which often are prompted by weather severity and which sometimes are reversed if winter weather moderates, deer generally move less and eat less in winter. Both are natural responses triggered by shorter daylight periods.
Deer dispersion
Department of Natural Resources researchers Christopher Jennelle and Glenn DelGiudice have enjoyed lifelong fascinations with wildlife. Their deer studies are helping to better inform the state's whitetail management and might someday contribute to higher deer survival rates, including in winters of extreme cold and deep snow.
In 2018, Jennelle began a study of southeast Minnesota fawns intended to determine whether these young animals disperse from their birth areas, and if so when and at what distances.
At the time, the southeast was the only place in Minnesota where chronic wasting disease had been found in wild deer (it's since been found elsewhere in the state in wild deer). Knowing whether southeast deer move significant distances during one season or another and in what directions might help explain, and predict, Jennelle said, ways CWD can spread.
Previous studies suggested bucks typically migrate, or disperse, greater distances than does, Jennelle said, adding that bucks have a greater likelihood of being infected with CWD.
"We captured 225 older fawns and fitted them with GPS collars," Jennelle said. "Our study was centered near Preston in the southeast. We found, generally, that movements of these deer was westward, with the average buck traveling 23 kilometers [about 14 miles] and the average doe about 20 kilometers. The farthest dispersal was 75 miles."
Data gathered are still being analyzed. But indications are that dispersals of young southeast deer — which typically began in May of the year following their births — are linked to searches for preferred habitats away from their birth areas. These quests for these new "home ranges" are likely survival behaviors, Jennelle said, linked to searches for areas of lower deer densities.
"They're looking for food and cover," he said, "perhaps in areas where competition for these resources is less."
The study also showed some southeast Minnesota deer migrate to Iowa in spring and summer before moving back to Minnesota in winter. The deer might shift south to feed in corn and soybean crops, Jennelle said, before returning north after the crops are harvested.
DelGiudice, meanwhile, is a 30-year DNR researcher who is studying two herds of radio-collared deer, one in an area about 29 square miles near Orr, the other near Longville, covering about 18 square miles.
Recent technological breakthroughs, DelGiudice said, are aiding his studies, whose ultimate goal is to optimize, concurrently, deer habitat and timber cutting.
"The latest GPS collars we're using give us 500 to 600 locations per deer per winter, in all sorts of weather, whereas in the past, with the technology we had, we might get 25 locations per deer, and then only in fair weather," DelGiudice said. "Using other technologies we have, we can determine the tree and vegetation species that deer in these locations prefer at different times of year, and the mix of those tree and vegetation species in relation to one another. The goal is to synthesize these findings with foresters' needs so cuttings can be designed to benefit both deer habitat and forestry."
In a previous 15-year study that DelGiudice completed of northern Minnesota deer, he found that migrations to winter yards are highly variable. About 65% of deer migrate an average of 5 to 10 miles, he said, with some traveling as far as 22 miles. But 35% of deer don't migrate.
"Dense pine stands in wintering areas do provide less snow, but they don't have much food for deer," he said. "Cedar and balsam fir stands are better. Most important are the sizes of these stands, their shapes, the amount of 'edge' they have and whether they're adjacent to forest openings and nearby food.
"When we complete this study and analyze the data, it will greatly advance what we know about managing deer and deer habitat, and forests."
Dennis Anderson • danderson@starribune.com
