By: Wade Nolan Bowhunting Biologist
The winter of 2012 in the Midwest and East didn’t show up. More global warming I suspect. I’m starting to really enjoy this warming but for me it is as easy as adjusting the thermostat. Staying warm during harsh winters for the whitetails we hunt is a full time job that has a multitude of requirements. Some of which you can manipulate.
Whitetails come with some very specialized physiology for maintaining their body at 104-degrees all year long. The hollow crenulated hair that they put on for the winter is one important adaptation that allows them to stay warm when wet or when temperatures dip below zero. All they need to survive is enough food to keep the furnace burning. During harsh winters, mortality can range as high as 50% if they lack food and cover.
During the winter, their primary fuel is browse. Browse is the woody stems and twigs of deciduous shrubs and trees. Deer need about 6-7 pounds of quality browse daily to maintain good health in the winter. Even with adequate food, winter can be stressful but the whitetails know how to meet that challenge. They seek out thermal cover to keep them warm and protected.
Conifer trees like cedar, pine, hemlock and spruce provide thermal cover. These trees, when found in clusters, offer some special benefits to a deer in winter. First, they offer security cover where they can remain hidden from predators but even more importantly these conifer stands capture the warmth from the sun.
Even on a cloudy day, the dark canopy is gathering in and holding radiant energy sent our way via infrared and ultraviolet energy from the sun. You probably know that you can get sunburn on a cloudy day. That same principal warms the dark boughs of conifers. Put on your 10th grade thinking cap from those days in physics class and bear with me for three more paragraphs.
Here are the basics. The sun’s ultraviolet (UV) rays easily penetrate clouds. UV is not visible to the human eye as we have a UV filter in our eyes. Much of the energy from the sun arrives on earth in the form of infrared radiation. Likewise, infrared (IR) light is actually electromagnetic radiation blasting out from the sun with a wavelength longer than that of visible light. We can’t see it either.
Yet we’ve all seen infrared images that use the heat signature of IR to create a picture. Although we can’t see IR with our eyes we have developed devices to easily see IR at night. Thermal sensors and IR scopes used by the military…night vision. This technology detects heat or IR. Therefore, IR emitted from the sun delivers heat to planet earth and to those conifers we are talking about in the deer woods.
The heat transfer process includes the mechanics of thermal radiation and convection. Ever stand in front of a wood stove and enjoy the heat. That is radiant heat. When that heat is moved about the room via air currents, we are looking at convection. The same thing occurs when a deer stands under dark pines on a sunny day or even a cloudy day. The pines heat up and the air currents move the heat around. The amount of heat may not be as noticeable but it is still measurable and important to the energy budget of a deer.
In review, dense stands of conifers provide a thermal heating blanket for whitetails that help them combat the extreme cold in winter. To be most effective, the conifers should provide 70% closed canopy overhead. If your whitetail property lacks this thermal cover, get busy and plant some. Deer need it up north. If you are a visual learner watching this video clip on Thermal Cover may anchor the point for you.
Likewise, if you want to get the most out of the thermal base layers you wear during the fall and winter you must keep them clean and functioning. The way to do that is to keep the micro fibers squeaky clean. Only one engineered detergent can do that for you…Sport-Wash laundry detergent. Being residue free will preserve the wicking and insulating qualities of your high-tech gear. If whitetails had a way to get Sport-Wash, they’d be using it. www.atsko.com
Excellent article, once again, my friend. I can’t count the number of big deer who have snuck up to me through the pines on a cold day, or the number of beds I’ve found in the snow under the evergreens. One small point worth noting from a retired F-117 Stealth Fighter pilot. The IR target tracking systems we used in the Stealth were actually able to discern IR radiation during the daytime. It was more of a challenge than at night, due to the similar heat signatures coming off many objects, but we could do it, and we did, though only during practice flights, as no one wanted to be out in combat during daylight hours in a Stealth Fighter. In a fight, we ruled the night.