Deer are great survivors in winter

Deer (by Ken Thomas on wikimedia)
Deer (by Ken Thomas on wikimedia)

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Chel Anderson is a botanist and plant ecologist. She lives in Cook County and joins us periodically to talk about phenology or what’s going on in the woods right now. Welcome, Chel.

Anderson: Hi, Jay.

Well, it is the dead of winter, as they say. Time to check in with our four-legged friends: deer. How are the deer doing?

Anderson: Yeah, well, deer are definitely among us. I think we’re all very aware of deer and they’re one of those creatures of our landscape that are so beautiful and so graceful and really a wonder to behold. But, they also pose some challenges to us because of some of their behaviors related to winter. So, let’s talk about the deer and why they do what they do and how they sometimes end up crossing paths with us in ways we would prefer they didn’t. To start with, the Whitetail deer is one of the most successful mammals on earth. It has a range from southern Canada to South America. So, this is a very successful animal. It has learned to adapt to an amazing array of environmental conditions and habitats and including urban habitats, right? So, it’s really not that far afield to say deer are everywhere, you know, except the driest deserts and the most, totally inhospitable places.

Yeah, they hold deer hunts in Duluth, in the city.

Anderson: Yeah, in the city. So, deer are really amazing animals, but like all animals that stay through our winter, they have to be able to survive the rigors of winter which basically come down to an animal has to be able to live within an energy budget, and the energy budget consists of the fuel you can consume, find and consume, and the energy it takes to move around and get it and to avoid predators. They need to be able to deal with the temperatures. They also need to be able to deal with the depth of the snow, and they have to have food; those three things. For deer, good food resources are basically woody vegetation; shrubs, small trees, that’s what they are surviving on. So, they need to have an adequate amount of that wherever they are spending the winter. Then, for temperature, they come equipped with a wonderful fur coat. And, as anyone who spends the year here knows, they are a different color here in the winter than they are in the summer. So, the coat acts both as a camouflage, but also as a thermal regulatory device. And, in the summer, we have that nice, reddish coat that is very thin that allows the deer to reduce heat stress. Then, in the fall, that color begins to change, begins to lighten up to grey-brown, and that’s as the winter coat comes on and the molt happens and the guard hairs grown out about two inches long, these very fluffy guard hairs that come out and then underneath that is a very dense, dense layer of shorter hairs. And the combination of those guard hairs trapping air between the outside and that underlayer of hair and then the density of that fine layer underneath, that is a tremendous insulator. So, deer, moose as well, you see them walking around the woods sometimes with this blanket of snow on their backs, because they are so well-insulated, that heat-trapping device of their fur coat is really, really excellent at keeping them warm.

Deer yard, what is that and why?

Anderson: Yeah, let’s talk about that. So, we talked about how temperature is an important thing; they have to be able to regulate for, and they have their coat. But, the coat alone isn’t necessarily going to work when it’s 40 below and the wind is blowing 30 miles an hour. So, deer definitely take advantage of thermal cover. We’ve mentioned this before, too. So, thermal cover is a place where there are coniferous trees growing—hopefully in a group, but even just one will make a difference—and with branches that come down close to the ground. So, this is primarily balsam fir, spruces, and cedars, or young conifers of other kinds, but the branches have to be down closer to the ground, not towering way up high. That keeps the air from moving away from the ground so quickly. So, it holds—I mean, it sounds silly. I mean, thermal cover when it’s 30 below? But, it does make a difference how quickly the heat moves away from you, as the animal, and the ground. So, those needles help slow down that movement of air and they can also act as a windbreak. So, if you’re a smart deer, you’re going to find a place out of the wind, could be in a grove of conifers, might be behind a ridge, you know, where the landform creates a block to the north wind or whatever the direction of the wind. And they also then can find themselves leaving behind what is a solitary and widely-space life during the summer as either box-isolated male deer or small family groups of does and their fawns. That kind of falls apart during the winter, because the deer tend to go to these places that offer them the best shelter. And, as the deer yard there, they pack down the snow, just from their movements they pack down the snow. So, then they start to improve the condition with respect to that other winter feature that we haven’t talked about yet which is snow depth, which might be the most critical factor for deer. Deer are very well-equipped to deal with our temperatures, but because they can’t grow longer legs, they can be very stressed by snows that surpass about 15 inches in depth, because they’re having to bound everywhere they go, otherwise they’re wading, and they can’t drag their legs through the snow particularly once any kind of a crust develops. And, if the snow gets to the point where it’s 20 inches, than even larger deer begin to drag their bellies and their chests, so think in terms of yourself being out without a trail in 24 inches of snow or more and how that feels like wading. I mean, the energy you expend to just go a short distance is huge. So, that’s when the energy expended to get to your food begins to exceed what you can gain from eating that. If you can, you move to places where there isn’t so much snow, maybe really packed down by deer in the yard, or in the case of where we live, we have one very huge deer yard, which is right here close to the lake. Because, close to the lake we have, typically, milder temperatures and we have lower snow totals. So, as the snow builds inland, they will begin to move down toward the shore. And, eventually, they, many of them, will spend the winter here, or much of the winter here, because of the factors that I just mentioned. That’s why it’s not just a figment of our imaginations that there are more deer by the shore in the wintertime than there are in the summer, because many of the deer that have lived the rest of the year inland have come down to the shore.

Chel Anderson, botanist and plant ecologist. Thanks for helping us understand what the deer are doing.

Anderson: You’re welcome, Jay.


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