Can deer freeze to death when severe cold weather, such as dangerously low temperatures, deep snow and crushing winds, set in? Although this winter has been warmer than average for much of the country, many areas have still experienced short spells of brutal conditions that, unfortunately, lead to human loss. So, it’s a logical question to ponder.
Deer are the most abundant and widespread large mammal in the Western Hemisphere and range from parts of South America all the way to Alaska. Yet, the northern extent of their range is constrained by the same Arctic conditions we temporarily experience when a “polar vortex” bears down and brings with it bone-chilling temps. All it takes is one or two consecutive years of extreme winters at this northern frontier and local deer populations can be reduced by half.
However, deer in these places are not directly succumbing to the weather. If that was the case, we would observe massive die-offs when air temperatures reach record-breaking levels, exposing southern herds to conditions they’ve never experienced before. Deer are survivors and they rely on a variety of behavioral and physiological adaptations to persist.
How Deer Prepare for Winter
A major winter survival adaptation is a deer’s feeding habits leading up to and during winter, including strategically utilizing the fat gained from those habits. Deer gain as much weight as possible during fall by concentrating on foods high in sugars or carbohydrates. Then they rely on their stored fat as an energy source during winter. They are similar to bears in this behavior, except deer don’t hibernate.
In fact, scientists found that adult does can get more than 50% of their daily nutrition from their fat reserves in winter! Bucks can lose up to 30% of their body weight during the rut but normally had gorged themselves so much prior that their fat supply remains a lifeline.
Following the rut and entering late winter, all deer voluntarily reduce their daily activity, including basic moving around and even feeding, to slow the burn of those fat reserves until the first green plants emerge in spring. As crazy as it sounds, faced with extreme winter weather and having already lost weight, deer eat less. Even captive deer with unlimited food available reduce their daily consumption and continue to lose weight during winter.
Why? If you think about it, from a survival standpoint and proliferation of the species, relying on the best winters when temperatures are mild and food is abundant doesn’t make a lot of sense because those conditions are rare occurrences. So, deer have adapted to live through the worst winters possible. It’s probably one reason they’ve survived for so long.
However, there is a limit to this strategy and the supply of fat reserves that carry them through winter: time. Researchers have shown that a typical healthy doe begins winter with a 90-day fat supply. Deer can survive almost anything Mother Nature throws at them during those three months. The ticking clock begins winding down in March and is the reason why weather patterns in this month often play the biggest role in winter deer mortality.
If you’re concerned about deer survival, the best thing to do to help them get through the critical last days is break out the chainsaw and provide more of the food they are adapted to eat in winter.
Deer Behavior During Severe Weather
People avoid severe winter environments by simply changing locations to get away from the cold. Even though deer don’t have the ability to go inside or fly south for a few months, they in essence do the same. In general, deer will move to and congregate in areas that provide the best protection from the weather when conditions aren’t favorable, such as seeking shade when the mercury rises.
In winter, this behavior is commonly called “yarding.” In most cases, yarding areas are warmer, less windy and offer better mobility than anywhere else. In much of the country, deer might just bed on south-facing hardwood slopes within their home range to take advantage of the direct sunlight. Or, in more northern climates, they can search for, travel to and find refuge in “deer yards” that may be well outside their typical home range. These traditional yards are often mature, select conifer stands with dense canopies, and they can be historically important with multiple generations of deer using the same spot.
Less common in white-tailed deer but more common for mule deer are true, long-distance migrations, which allow entire herds of either species to avoid harsh conditions at higher latitudes or elevations during winter and take advantage of high-quality forage during summer.
A Deer’s Winter Diet
Reliable winter nutrition for deer primarily comes from stored fat and water and is merely supplemented with items they consume at this time of year like buds, twigs, bark and dead leaves. Preferred winter forages include shoots of woody browse from small trees and shrubs, the same from a few select coniferous species, and any persistent fruits or leaves. There’s actually not a lot of difference in the nutritional quality of the things they eat in winter; quantity is more important. In fact, the true value is not in the calories but in the creation of internal heat via the digestion process.
In most cases deer will key in on foods that are closest to where they’re spending the majority of time described above. That means if there is not much forage available within reach in those places, the rate of fat loss will be greater than normal.
Of course, regular habitat management practices help enhance the quality of deer habitat in the long run, like producing more browse and cover at ground level for future winters. But, if you’re concerned about deer survival, the best thing to do to help them get through the critical last days is break out the chainsaw and provide more of the food they are adapted to eat in winter near where deer spend the coldest months.
Bodies Built for Winter
Perhaps what makes deer the most bullet-proof to severe winter conditions, however, are their physiological adaptations. First is their body size.
The further north a deer lives, the more likely that individual will be larger and have more compact appendages compared to its relatives from a more southern climate. This is called Bergmann’s rule and allows a species to save energy and conserve heat to inhabit inhospitable conditions found at the fringes of its range. The average mature Florida whitetail buck weighs about 150 pounds while in Canada the average is 300-plus pounds, a perfect example of Bergmann’s rule.
Second, deer shed and grow two coats per year, and the one they don in winter is key to their ability to deal with freezing temperatures and precipitation because it carries important thermoregulatory qualities. For example, a deer’s winter coat is five to six times thicker than it is in summer, and it is made up of long, hollow guard hairs and short underfur. This combination insulates deer so well that snow can ride on a deer’s back without melting from body heat.
Finally, deer have a musculoskeletal adaption that allows them to stand in deep snow for days or weeks on end without feeling cold toes. The bottom half of all four legs on deer are composed of a keratin hoof that makes contact with the ground, followed above that by a long carpal bone (basically to what most consider the “knee”) that is encased in tendons rather than true muscle. Tendon is a comparatively poorly vascularized tissue that requires very little blood flow. So, deer can walk through a foot of snow as if they are on stilts.
Though logical in theory, deer do not reduce their metabolism during winter as a winter survival strategy, which is a falsehood that’s been unfortunately perpetuated by writers and even some fellow biologists for decades. The truth is that a deer’s metabolism varies little across the seasons.
Can Deer Freeze to Death?
So, to answer the question: Can deer freeze to death? No, deer don’t get hypothermia or freeze to death, and they have some amazing abilities to withstand insanely cold winters. That said, you clearly care about their well-being enough that you’ve read this far, and there are ways that you can help the next time we see things go north quickly.
More often, deer die naturally from starvation or predation in winter, and it’s frequently the youngest, oldest and weakest that succumb. Generally harsh winter conditions exacerbate these factors, and these other forms of mortality are seen more where there are short growing seasons, numerous predators, and large expanses of the landscape that lack appropriate yarding structure and/or forest disturbance and early successional cover that is important to deer.
In such places, you can work to improve fawn recruitment and overall herd productivity primarily by adjusting antlerless harvest intensity and improving habitat all year long. These are a deer manager’s quickest and most efficient tools to provide a buffer the next time we experience a bad winter.