Deer Population Data
Why spend the effort to collect deer population data? Simply, the information is necessary to successfully manage deer in many situations. Proper management of any resource, including deer, begins with establishing goals, learning about the resource, and inventorying the resource. The inventory process for deer management should include both deer habitat and the deer population. Habitat evaluation examines the soils, water, plants, space, and their interrelationships on the management area. Evaluation of a deer population involves examining several parameters of the deer herd.
Deer population data refers to information collected about a group of deer from a specific geographical area such as a ranch, deer management association, county, state, etc. Deer population data is used to interpret herd health and evaluate population status relative to the goals for a population. There are many different types of population data that can be collected. Some examples of useful and commonly collected data are listed below:
- buck antler characteristics (i.e., basal circumferences, points, main beam lengths, and spread) for specific buck age classes, especially yearlings (1 year old) and mature bucks (>4 years old)
- body weights of certain buck age classes, especially fawns, yearlings, and mature bucks
- body weights of certain doe age classes, especially fawns, yearlings, and mature does (>2 years old)
- mortality due to hunting
- buck population age structure
- doe population age structure
- fawn crop
- adult deer (>1 year old) sex ratio
- deer density
Management goals should influence the type of data collected. For some goals, there is very little need to collect deer population data. An example would be a park or private landowner whose primary goal is to simply have deer, but not allow hunting and is not concerned about any specific deer herd health issues. Deer population data probably is not needed in these situations, but the managers probably should monitor habitat. Several things can degrade the plant portion of deer habitat such as plant succession, land management practices, and overabundant deer or livestock.
Management goals involving light to moderate intensity hunting probably can be adequately served with population data collection techniques such as harvest records and daylight cruise surveys. Harvest records simply involve collecting data from harvested deer. Harvest records should include the following minimum information for harvested deer: harvest date, sex, age, weight, and buck antler characteristics. Sometimes additional information is recorded depending on need, such as kill location (pertinent for large management areas), Boone and Crockett score, lactation status, ovary corporalutea counts, kidney fat index, and depth of back fat.
When the management area's total deer harvest is less than 500 deer, the records should attempt to include every deer harvested. If the harvest is more substantial, a sample of the total harvest should be adequate. Several population parameters can be gleaned from harvest records, such as buck antler characteristics, buck weights, doe weights, mortality caused by hunting, and to a lesser extent, buck and doe age structure. Age structure information from harvest records often does not accurately represent populations because harvests tend to be age and gender biased due to preferential harvests (bucks versus does) and increased susceptibility of yearlings and fawns.
Much can be learned from harvest records. In fact, if limited to only one technique for collecting population data from a hunted population, harvest records should be the choice of techniques. Noble Research Institute wildlife specialists can provide sample forms for recording deer harvest data.
Daylight cruise surveys involve riding around the management area looking for deer during September and late August. Deer should be identified and recorded as buck, doe, fawn, or unidentified deer. This information can be used to determine fawn crop and adult sex ratio. More detail about daylight cruise surveys is available on page 28 of White-Tailed Deer: Their Foods and Management in the Cross Timbers, available from The Noble Research Institute Agricultural Division, and Collecting and Interpreting Deer Spotlight and Daylight Cruise Survey Data, which should become available this fall.
Management goals involving moderate to heavy intensity hunting are served best with population abundance estimation procedures in addition to harvest records and daylight cruise surveys. The spotlight survey is the primary technique used to estimate population abundance in Oklahoma and north Texas.
The spotlight survey also provides data for determining fawn crop and sex ratio. Deer density information collected during population abundance estimation procedures such as spotlight surveys is probably the least precise and least accurate population data addressed in this article.
However, spotlight survey data provides an index to population abundance often necessary for management decisions such as formulating harvest strategy. Trends from multiple years of spotlight survey data are probably more meaningful than spotlight survey data from individual years.
When spotlight surveys are used, they should be conducted several times each year to moderate variability inherent with the technique. Spotlight surveys can be conducted from mid-August through March to estimate deer density, but are usually conducted during September and late August to provide fawn crop, sex ratio, and density information for formulating harvest strategy prior to hunting season. Local state game wardens should always be notified before conducting spotlight surveys. Much more information about conducting spotlight surveys is included in the two publications mentioned above.