MDNR Estimating Deer Population Numbers

by MS.com staff on August 26, 2011

Scientific estimates of wildlife numbers and information about population trends (increasing, decreasing, or stable) are necessary to successfully manage wildlife. For more than 50 years, the Michigan Department of Natural Resources (DNR) has worked very hard at estimating deer population numbers. Each year, wildlife biologists use this population estimate to adjust hunting season rules and regulations to meet the DNR’s long-range deer management goals to.…

Maintain a deer herd that is in balance with its habitat and that yields healthy fawns, does and bucks;

Maintain a quality deer herd to meet the social, economic, and recreational demands of the public, while considering public safety and the carrying capacity of other native species, native plant communities, agriculture, horticulture and silviculture; and

Maintain a quality deer herd to provide diverse quality recreational experiences for those wishing to hunt deer and those wishing to view them.

White-tailed deer populations, like other wildlife species, fluctuate in size from year to year, as well as from season to season. Annually, they reach their highest number by early summer, following the birth of fawns. Predation, disease, vehicle-deer crashes, hunting harvests, and winter losses due to starvation reduce their numbers during the rest of the year. Various survey techniques have been designed to assess these losses and provide wildlife managers with information to estimate the size of Michigan’s deer herd. These techniques fit together like the pieces of a jigsaw puzzle all of them are needed to see the entire picture. Following is a brief description of the time-tested surveys that the DNR has relied upon for managing Michigan’s white-tailed deer.

Deer Harvest Surveys

Hunting harvest information is the foundation for monitoring the deer herd. Hunting is the major source of population reduction. Mail surveys, rather than mandatory registration, are used to estimate the legal deer harvest each year. Following the 1999 deer season, nearly 1-out-of-16 deer license buyers were mailed a survey questionnaire requesting information about their hunting season results. These scientifically random samples of license buyers provide reliable estimates of the deer harvests by county. Hunter success and the ratio of young to older-aged deer in the harvest provide wildlife biologists with additional information about the status of local deer populations, such as population growth and sex ratios. Scientists around the world recognize our mail survey techniques for their excellence.

Summer Deer Observations

For nearly 70 years, DNR wildlife biologists, conservation officers, foresters, and other field employees have recorded the numbers of deer seen during daylight hours during the period from July 1 to October 31. Changes in sighting rates (the number of deer seen per hour of effort) reflect changes in the deer population. Summer deer observations provide wildlife biologists with one measure of fawn production that is critical for estimating population size. Deer observations are also useful for forecasting upcoming hunting seasons, identifying areas where deer numbers are changing, and for assessing the sex and age composition of local deer populations.

Check Station Data

Last year, DNR employees checked and recorded physical data for approximately 43,000 hunter harvested deer brought to highway deer checking stations and DNR offices. Experienced deer “agers” determine the sex and age of each animal, count antler points, measure antler beams, and check the general condition of each deer. Deer are also examined for bovine tuberculosis. Antler points and beam diameter measurements provide biologists with an index of the physical condition of local deer herds. Age and sex information for harvested deer is compared with similar information obtained from summer deer observations, to assure that the best available data are used for estimating the deer population size each year.

Traffic Survey

The sole use of the deer traffic survey is to provide an early estimate of the firearm season deer harvest. Michigan’s strong deer hunting tradition has always captured the interest of news reporters who are eager to report the deer hunting season results. DNR employees count deer on vehicles as they pass by observation points along the four major north-south highways in the Lower Peninsula. Deer “agers,” who are stationed at deer checking stations at highway rest areas, help with this estimate. They determine whether deer are visible to highway counters. The traffic survey results are then adjusted for those deer that are not visible to highway counters. The results of the deer traffic survey closely match with mail survey results, which are not available until spring.

Pellet Group Surveys

DNR field employees are busy with deer pellet surveys during the spring season. This survey provides a useful index of deer distribution and abundance from year to year in the northern-forested areas of the state. Pellet group surveys do not work well in areas where intensive agricultural activities disturb evidence of deer. Since 1950, field employees have counted pellet groups along random survey courses to determine the relative number of deer within a defined area. These counts are generally expressed as deer per square mile.

Dead Deer Searches

Dead deer searches are done in conjunction with pellet group surveys. Teams of Wildlife personnel count the number of dead deer they locate while walking pellet survey courses. When a carcass is found, a determination is made whether the loss occurred during early or late winter. Over-winter loss is a major source of non-harvest mortality to deer on the northern fringe of their range. The results of dead deer searches are used with pellet group surveys to estimate spring deer populations.

Car-Deer Crashes

A common deer population index in the Midwest is the number of car-deer crashes reported to law enforcement officers. Several research studies from across the country indicate that car-deer crashes are related to road densities, traffic volumes, and deer densities. The Michigan State Police and the Michigan Department of Transportation maintain data on the number of car-deer crashes and traffic volumes. Recent findings by Michigan State University demonstrate the usefulness of these data to wildlife managers since a correlation exists between county car-deer crashes and the buck harvest. Car-deer crashes are also used to estimate additional non-harvest mortality.

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