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White-tailed Deer Research Projects - Buck Mortality Study

Immobilized buck being removed from a drop net.

Immobilized buck being removed from a drop net.

Hunter harvest is the largest cause of death in bucks. Biologists refer to the portion of bucks killed by legal hunters each year as the buck recovery rate (BRR). The buck recovery rate is a key component of accurate deer population estimates. In 2006, a panel of experts in big game population modeling recommended that we document BRR through a long-term mark-recapture study, thus making this study a top priority. As the name suggests, this means capturing and tagging bucks, monitoring their activity, and determining the causes of buck mortality, or death.

In the past, BRR has been estimated for each deer management unit based on local expertise and modeling, rather than direct measurements from the field. Estimates of BRR across the Midwest have ranged between 53-90%.

One of the important assumptions of the Sex-Age-Kill (SAK) population formula is that the aged sample of registered bucks is representative of the age structure in the population. For example, if 50% of registered bucks were yearlings (1-year old), the assumption would be that half of the adult bucks in the entire population within that deer management unit are yearlings. However, hunter selection for larger and older bucks, and increased yearling buck vulnerability to harvest may introduce error to this statistic. The results from this study will provide a better estimate for BRR over a variety of deer habitats.

Study Area

Two study areas have been established; one primarily forested area in northwest Wisconsin, and one farmland area in east-central Wisconsin. The different study sites were chosen to monitor differences in buck mortality and harvest rates across areas with different habitat types, hunting pressure, types and relative densities of predators, and vehicle traffic.

Study Areas for Buck Mortality Study.

Study Areas for Buck Mortality Study.

Study Design

This study will run concurrently with the Predation Study in the same study areas. The study will begin the winter of 2010-2011 and continue for at least five years. The objective is to maintain 30 radio-collared and 100 ear-tagged male deer in each study area over the duration of the study.

Deer will be captured using a variety of methods that may include live traps, rocket nets, net guns used in conjunction with helicopters, drop nets, or tranquilizer darts. We will attempt to minimize the handling time, stress and injury to captured deer.

Radio-collared deer will be monitored frequently to determine timing and causes of mortality. When a deer dies, the collar will send out what's known as a "mortality signal." If the deer is not bagged by a hunter, the researchers can locate the deer and attempt to determine the cause of its death. Hunter cooperation will be critical to our success. Hunters in the two study areas should be aware that deer may be marked with radio collars and/or ear tags and if they harvest a marked deer, they should report that to DNR. Marked deer (either radio-collars or ear tags) are legal game and hunters should not let the fact that deer research is being conducted influence their decision to harvest a deer. One of the objectives is to measure deer mortality caused by hunting. Thus, hunters are encouraged to hunt as they always have and treat marked deer like any other deer they may encounter while afield.

Last revised: Friday October 06 2017