Sponsored by: Whitetail University, Atsko Products


By: Wade Nolan
bowhunting biologist
Oct 23, 51/Sept 22, 18

As a wildlife biologist I’m prepared to be astounded by the physiology of animals. Deer, which I spend a lot of time focusing on may be my favorite. They are perfectly designed to fit into their habitat. I live in Pennsylvania so the deer I see most often have to endure a wide swing of temperatures every year. Last summer it hit 98 on my farm and last week it was 1-degree Fahrenheit. That’s a lot of swing. The deer that live here have to have a strategy to survive both extremes.

The biggest factor in temperature regulation that a deer relies on is his coat. Thin in summer and thick in winter but there is more. During the winter their hair thickens and becomes longer and denser. Their adaptation that allows them to be cozy when the temp drops below zero is that their hair is filled with air. It is interesting to learn that all animal hair is unique. A microscopic view shows that a deer’s hair is made up of overlapping scales. Although a moose or caribou are relatives their hair is as different as fingerprints.

This is winter coat of a white-tailed deer. Note how dense the hair is and how the dark guard hair forms the otter barrier. Deer hair is famous for use in fishing flies because the hair is hollow and floats.

Deer can change the orientation of their hair in a strategy called Pilo-erection. This is when they command their hair to stand taller and give the appearance of being fluffed up. This makes them look bigger but the benefit is that it increases the percentage of air space between individual hairs, offering them more insulation.

Not much difference than a Styrofoam cup, their hair is designed to insulate them and act as a barrier to the wind. Guard hairs are the long ones that are colored at the tips. This dark coloration actually helps capture the sun’s radiation. But most of the heat a deer relies on originates from burning calories.

Deer hair is relatively straight. This is common in hair follicles that are round. Flattened hairs are curly.

Just like your furnace at home a deer’s internal thermostat regulates energy flow and as long as their belly is full they can endure extreme cold. During the winter months, a whitetail deer relies on browse which is the woody stems of deciduous twigs. They need about six pounds of browse a day. That’s a lot of twigs.

Deer do understand thermal cover. When it is cold they can bed under cedar or pine trees and avoid the open night sky, which is a heat sink. The cover protects them from a loss of heat through radiation. When you see a fluffed-up whitetail on a cold winter day he is making the most of that deer hair. It’s part of the magic of deer physiology.

Sponsored by: Whitetail University, Atsko Products

Wade Nolan was an interesting, educated, committed hunter, author, videographer and wildlife biologist who loved what he did and loved spreading the word of Christ. He passed away Sept 22, 2018 after a long battle with cancer. We will try and continue his legacy with past and new articles. For more please go to Wade’s web site, www.wadenolan.com/about.html 

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