Seasonal habitat requirements of northern white-tailed deer
By Matt Ross, Whitetail Stewards, Inc.
Food
Spring
As snow melts in the early spring, the first herbaceous plants to become green provide deer with high-energy foods until buds of shrubs and trees begin opening. At this time, northern deer will spend most (67%) of their feeding time foraging herbaceous plants and will consume any available native and agricultural grasses, ferns and sedges. In the Midwest, early-season agricultural crops (e.g., clover, alfalfa) can make up a significant portion (89%) of a deer's diet.
As forbs and young leaves become more available during early summer, northern deer shift from a strict diet of grasses, ferns, and sedges, and begin eating a mixture of herbaceous vegetation, young leaves, and the current shoots of woody species. In late summer, woody plant parts become less important, and deer focusing their attention solely on green leaves, brambles and available forbs.
In autumn, northern deer require a high-energy, digestible food source in order to acquire fat for the upcoming winter. However, by autumn, most green vegetation has become dry and dormant and has low palatability. At this time of year, soft and hard mast (fruits and nuts) become available and are a required component in the diet of northern deer. During years of heavy acorn production (up to 200 lbs/acre), acorns may comprise over 50% of the daily diet of deer. During years when acorns are scarce, deer will seek out seeds and fruits from other plants. Deer will also consume persistent green leaves from brambles and groundcovers, and mushroom will comprise a small portion of the diet. Woody browse is an important component of the autumn diet of northern deer.
Winter in northern regions usually brings deep snow that limits the availability of most foods to deer. As a result, the winter diet of northern deer consists almost entirely (over 80%) of coniferous and deciduous browse and bark. Dry leaves, evergreen ferns, and plants with persistent winter fruits (e.g., mountain ash, hawthorn, rose hips, sumac, and poison ivy) are also important. Following an abundant mast year, deer may paw through more than one foot of snow to find and eat acorns. Once deep snow and cold temperatures are common, any plant that provides food within or near winter cover is typically consumed first, regardless of its palatability.
In winter, northern deer experience what is called a "negative energy balance" as a result of the poor availability and quality of winter food. This means that food quality is so poor that deer are unable to eat enough food to maintain their body weight, and as a result, they loose weight (mostly fat) throughout winter. (Research has shown that even when northern deer are provided high-quality supplemental food during winter they still loose weight.) Because winter food is of such poor quality, deer rely on stored body fat for as much as 30% of their winter energy requirements. Additionally, deer reduce the amount of food they require by reducing their activity and by selecting winter cover that provides shallow snow depths and warmer temperatures.
Northern deer populations are often exposed to severe winter conditions; cold temperatures and deep snow force them to congregate in sheltered areas known as "deer yards" or "deer wintering areas". The primary reason for this behavior is to conserve energy.
Coniferous (evergreen) plant species such as northern white cedar, hemlock, balsam fir, and spruce are usually used as preferred winter cover. Specifically, deer prefer dense stands of coniferous trees that are at least 35 feet tall and provide at least 65% crown closure. Northern white cedar is highly-preferred by deer because it not only provides good cover, it also is a high-quality winter food, and is more digestible that other conifer species.
Preferred winter cover offers deer a stable temperature, a high and stable relative humidity, low wind, and a firm snow pack; all of these conditions reduce the amount of energy deer must use when walking and to stay warm. Ideally, preferred winter cover should also be near some source of winter food. However, during extreme winter conditions, yarding behavior is such an innate response that deer seek winter cover even if food there is sparse or non-existent. In general, deer will move to winter cover when snow depths exceed 18 inches and temperatures are below freezing.
In mountainous areas and at the northern edge of their range, deer may move long distances to find suitable winter cover. Deer have been documented moving as much as 4 miles to over 50 miles between early-winter and mid-winter habitats. However, it is most likely that individual deer or small groups of deer (doe family groups or bachelor groups of bucks) make these large seasonal movements, and that mass migrations of entire deer populations are only myth.
Northern plains and midwestern populations of deer typically confront winter without the benefits of dense coniferous winter cover. Human land use in the past century has converted most of these states into a matrix of open (65-98% of total area) and forested (1-35%) habitat, with small "fingers" and "islands" of woodland found in lowlands (draws, swales, floodplains) and steep hillsides. Although these pockets of woodland provide ideal food and bedding cover during most of the year, during occasional severe winter storms, this habitat proves to be marginal and local deer populations may experience winter mortality.
Water
Most deer in northern regions have some source of surface water within their home range. However, in places where this is not the case, northern deer can survive for up to 15 days on water contained in their food (succulent vegetation), early morning dew, snow, and temporary rain puddles.
Space
In northern regions, home ranges of deer tend to be larger and less stable than in southern regions. Most northern deer maintain an oval or circular-shaped range between 5 and 10 miles long nearly all year. However, due to the severity of environmental conditions and lack of a diversified landscape in these regions, deer are often forced to slightly shift the center of activity within their home range seasonally. This displaced activity is usually a response to seasonal food availability and the availability of winter cover.
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