Research Studies - Deer

Estimating Deer Density Across Indiana - Zackary Delisle

A good estimate of the number of white-tailed deer in an area is critical for efforts by IDNR to manage the state’s deer herd. Our goal is to evaluate density estimation methods for reliability and cost-effectiveness in large-scale monitoring. To accomplish this, we will be estimating deer density using three different methods: fecal-pellet transects, trail cameras, and vertical-looking infrared (VLIR) aerial surveys from a small airplane. For all three of these methodologies, a “distance sampling” approach will be used to estimate deer density.

Fecal-pellet surveying is a common method used to estimate deer density. By estimating the density of fecal-pellet groups deposited by deer, density estimates of deer can be calculated if the following is known: the defecation rates of deer (how many times a deer defecates per day), how long fecal-pellet groups persist in nature before degrading beyond recognition, and the time period during which fecal pellets could have been deposited. Surveyors will walk and search randomly placed transects for fecal-pellet groups during March and April.

Because pellet groups farther away are more likely to be missed, the distance from the transect line to each observed pellet group will be measured to calculate a detection function for density estimation. Separate projects will also be conducted to determine how long fecal-pellet groups persist in nature before degrading beyond recognition, and the time period over which fecal pellets have been deposited (i.e., the time since leaf-off the previous fall, because leaves will cover all fecal-pellet groups deposited earlier). The results of prior projects that have estimated the defecation rates of deer also will be used.

Motion-triggered trail cameras will be evaluated to determine their efficacy at estimating density in local landscapes and across multiple counties. Browning Strike Force HD Cameras will be deployed in the same areas as the fecal-pellet surveys and mounted on trees in forests, grasslands, pastures, and wetlands. In certain areas of the state, additional cameras will be set on t-posts in row-crop fields, to assess deer density in agricultural areas. The distance from trail cameras to photographed deer will be estimated in order to calculate a detection function for camera sampling, which will facilitate an estimation of deer density. Cameras will be deployed in January and retrieved in early spring. All cameras will be marked with a sticker that reads “Purdue University Integrated Deer Management Project.” If you happen to come across one of these cameras, please do not touch or alter the camera, and contact the Project immediately to report damage or vandalism.

Purdue University also will estimate deer density by flying aerial transects with a small airplane. The sampling protocol for flying aerial transects is fairly similar to walking transects and searching for fecal-pellet groups on foot. However, instead of walking randomly placed transects, transects will be systematically flown in an airplane; and instead of searching for fecal-pellet groups, infrared cameras will be used to search for deer from the airplane.

A high-resolution digital camera also will be used to confirm that a heat signature detected by the infrared camera is actually a deer and not a goat, cow, sheep, coyote, or other mammal that can give off a similar heat signature. The distance from the centerline of the infrared video to each heat signature will be measured using computer software and will be used to calculate a detection function for estimating deer density. Aerial transects will be conducted during March in the same areas that fecal-pellet and trail-camera surveying are conducted.