A white-tailed deer standing next to Douglas fir trees, known as a lifeline winter food source for deer in winters with cold temperatures and deep snow.
A white-tailed deer browsing parts of a shrub that is sticking out of the snow. Shrubs including serviceberry, red-osier dogwood, willows and chokecherry are all important winter food sources.
As the seemingly endless winter snows begin to turn to rain and our valley snowmelt begins to fill our streams and wetlands, it finally appears that spring is here. A winter like this one is an uncommon event, maybe occurring once every 10 to 20 years. For some of the wildlife in the Blackfoot watershed these events can be life giving times of plenty. For others, it can be a struggle to survive with many losing the battle.
The winners tend to be those species with adaptations for deep snows and cold temperatures. Species like the snowshoe hare with their disproportionately large feet that aid their mobility in deep powdery snow giving them access to overhead forage and an ability to escape predators; predators like the Canada lynx, another species with winter adaptations. Large feet and a relatively light body help the lynx thrive in deep snow conditions where other predators may struggle. This adaptation allows the Canada lynx to outcompete coyotes and bobcats for prey and avoid their heavier bodied enemies like the mountain lion.
Some of the losers tend to be more noticeable like deer and elk. White-tailed and mule deer can certainly thrive in cold climates but extended periods of extreme cold temperatures and deep snow have high-energy demands on both species. Elk are better adapted to winter with their long legs and larger body size but as snow starts to crust, travel and foraging can be challenging for them too.
As these challenges add up and winter drags on, elk and deer increasingly rely on stored energy in the form of fat reserves from the previous summer and fall. Summer and fall forage has been determined to be the most important for winter survival and reproduction in deer and elk. Winter forage is low in digestible energy relative to summer forage and does not allow for deer and elk to maintain body condition. The prolonged exposure to the cold temperatures and deep snows will eventually take their toll on the deer and elk, especially the young and old. Many will potentially not make the following summer.
Winter die-offs of deer and elk typically occur during March and April. The cumulative effect of high-energy expenditure and energy deficient forage has the greatest affect at winter's end. However, a larger than normal winter die-off provides others with an opportunity for survival.
Raptors and scavenging birds like the raven are suddenly provided with a bounty of food. Others like the coyote that rely on scavenging as much as hunting may also thrive.
To the hunter this may sound like a doom and gloom story with a resulting limitation of hunting opportunity the following autumn. As the biologist, and hunter, responsible for managing big game populations in the Blackfoot, I, too, have my concerns. But I also see this as a cautionary tale and even an opportunity to improve our big game management.
Winter is a limiting factor for deer and elk populations in northern climates. When winter forage becomes limited or overused and there are above average die-offs, it's a great indication that deer and elk populations have exhausted the resources available to them. Once the snow depth makes foraging for grasses too costly from an energy expenditure perspective, elk and deer will move to forested areas where they can feed on shrubs, lichens and conifer needles.
The signs are easy to see. Next time you ski or snowmobile or simply drive around the valley, notice the Douglas-fir trees with no needles within four or five feet from the ground. This is called the "browse line", the maximum height that deer and elk can reach. In a winter like this it is an obvious sign that forage is limited.
Douglas-fir is considered to be somewhat of a lifeline winter food source for deer. Other critical winter food sources include woody shrubs like serviceberry, red-osier dogwood, willows and chokecherry. Lichens that hang from tree limbs also serve as an important winter food source.
If we pay attention to these signs, we can see that our deer numbers maybe too high. To combat this, and avoid a major winter die-off, we can harvest additional white-tailed does (female deer). By harvesting more females, we improve conditions for the other deer by increasing the available forage and nutritional condition. The result can be an increase in pregnancy rates, healthier offspring and greater overall reproduction which can lead to a younger more productive deer population. This will also help to buffer the effects of extreme winter conditions and may help us avoid large die-offs.
To read more about the nutritional requirements of deer and elk in winter you can check out the Montana Fish, Wildlife & Parks Region 2 Wildlife Quarterly here: http://fwp.mt.gov/regions/r2/wildlifeQuarterly.html.
In spite of these winter challenges, deer and elk are resilient and have been through this before. The excess moisture stored in the snow will benefit our waterfowl, shorebirds, fish and contribute to a flush of spring vegetation for our deer and elk.
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