Winter Effects Big Game

Send by email Printer-friendly version Share this

White-tailed Deer

Whitetail-tailed deer are near the northernmost limit of their range in Maine and the severity and duration of winter weather exerts considerable influence on deer survival and abundance. Periodically, a severe winter (like last year) can cause high winter mortality and a population decline. Conversely, mild winters can enhance deer survival and aid in population increases.

Deer survival in winter is dependent on their mobility. Deep, unsupportive snow inhibits deer mobility and may prevent the animal from taking in enough browse to sustain it. Under these conditions deer are in a state of negative energy balance whereby the deer must reabsorb body fat to stay alive. Low air temperatures and wind create a further demand on the deer since it must generate more heat to maintain normal body temperature.

When severe winter conditions persist, deer become progressively weaker and malnourished until the animal exhausts its reserves of body fat. At this point, winter losses of a deer population begin to occur. Fawns of the previous summer are generally the first to go, although considerable mortality occurs among adults during very severe winters. Predation rate by coyotes, dogs and bobcats is also directly related to winter severity; losses to predation tend to increase overall winter deer losses above levels that can be attributable solely to under nutrition. Winter weakened deer are more prone to collisions with autos and trains at spring greenup. High losses of the following fawn crop may also occur after a severe winter. Malnourished pregnant does tend to produce weak or stillborn fawns, further adding to deer population declines.

Proper management of Maine?s deer resource requires a reliable estimate of winter severity so that prediction of winter deer losses, fawn recruitment, and possible changes in the size of the deer herd may be made. We measure the severity of winter in order to monitor population trends. High deer losses are associated with very severe winters, and during mild winters, mortality rates can be as low as three percent.

This department monitors winter from the beginning of December into late April. This week's snows prove that winter has not yet ended in Maine. A delayed stay of winter or a late spring is very detrimental to deer because the must remain on an inadequate winter diet at time when their metabolic demands are increasing to support body growth, pregnancy and/or antler growth. Deer fare poorly if they cannot access high quality forage in April.

We monitor winters by collecting data at 25 to 30 deer wintering stations strategically located throughout the state. At these wintering stations, we monitor snow depth, deer sinking depth and continuously monitor temperature. The resulting data is compiled into a winter severity index that allows us to compare the severity of winter throughout the state, and also to compare the present winter against past winters and the averages of past winters.

So how did deer do this winter? Since winter is not yet over, it is a question that we can't answer. This winter still is ongoing and we are still measuring snow depths and temperatures in deer wintering areas throughout the state. However, over the next month, we will have gathered all the wintering data we need, and biologists from throughout the state will convene and interpret just what has happened this winter, and how it affects Maine's deer population.


Maine moose are living near the southern extreme of the species? range. We like to think of Maine winters as tough. However, compared to what a moose in northern Canada or Alaska has to deal with, our moose face a winter that is short and warm. A calf moose does not increase the amount of heat it produces or change its behavior to keep warm until the temperature drops a little below -20o F (for instance, it could lie down in snow to increase the amount of insulation around its legs). The exact temperature at which adult moose need to increase their heat production (e.g., by shivering) in order to keep warm hasn't been established, but it is below -30o F. In other words, an adult moose is very comfortable in temperatures down to -30ยบ F. In fact, our moose are more likely to be troubled by the heat than the cold.

In its winter coat, a moose will need to take steps to keep cool when the temperature reaches the mid 20's. That's 20o Fahrenheit not Celsius! They will spend more time in the shade and not spend as much time moving. By early spring, it isn't unusual for a moose to seek relief from the heat by lying in water.

-Karen Morris, Wildlife Biologist

Black Bear

This department is busy throughout the winter monitoring bear. Field studies have been conducted on two different study sites since 1975 and a third since 1982. These long term studies that are made possible by radio-collaring female bears give us data on survival rates, population densities, habitat relationships and movements of bears. All of these guide our statewide management activities.

Currently there are about 60 radio collared female bears in our study sites, and annually we trap about 150 bears. Samples of radio collared females are maintained by collaring yearling female offspring of monitored bears in dens, and by the occasional trapping efforts during the spring.

The data that is collected on survival, reproduction and densities of female bears in these study areas form the analysis of the effects of food and harvests on black bear population growth. It also provides insight into the influence of beechnut production on reproduction rates and population growth.

Maine's large bear population provides a range of benefits to residents and visitors of the State. Our tradition of bear hunting is a healthy recreational activity that supplies successful hunters with excellent table fare and memories of good days afield, and drives a guiding and outfitting industry that helps to support rural economies. In recent years, the public's interest in opportunities to view bears has been fueled by the increased visibility of bears along roadsides during the spring and summer months. As our human population grows and the number of tourists visiting Maine increase, we will be challenged to address potential conflicts between bears and humans while maintaining our abundant bear population.

The Commissioner's Advisory Council has approved new bear management goals and objectives to drive the Department?s bear program through 2015. These goals and objectives were recommended by a public working group of citizen advisors, representing diverse interests in bears. The Department's bear management goal will be to provide hunting, trapping and viewing opportunity for bears through the 15-year planning period. Three management objectives were developed. First, we will strive to stabilize the bear population by 2005 at no less than levels experienced in 1999 (23,000 bears statewide), through annual hunting and trapping harvests. Second, we will create information and education programs by 2002 that target specific audiences and promote traditional hunting and trapping methods as valid and preferred tools to manage black bear populations in Maine. Third, we will create information and education programs by 2002 that target specific audiences and promote public tolerance of bears in Maine.

The new management objectives are ambitious undertakings. They will require more refined monitoring of bear populations and hunting harvests, and greater knowledge of bear habitat relationships. The new objectives will also require additional funding to support expanded research and population monitoring programs, and public information and education efforts. Given such support, the Department?s long-term bear management plan ensures that Maine will continue to be a stronghold for black bears well into the future.

-Craig McLaughlin, Wildlife Biologis