Most hunters probably don't know it, but they are census takers. Every year, the Wisconsin Department of Natural Resources calculates the pre-hunt deer population based on the number of bucks that hunters shoot. In deer management unit 77A, which includes most of Rock County, the percentage of bucks that were yearlings in 1999 was estimated at 67 percent. The percentage is based on deer aging. Every year, biologists visit between 80 and 90 of the state's 570 deer registration stations and examine the teeth of deer killed by hunters to determine ages.
Biologists assume that deer killed by hunters are representative of the entire herd.
The age structure of the herd tells biologists what percent of bucks die each year. If 67 percent of the bucks are yearlings, for example, that tells biologists that 67 percent of the bucks died the year before. In areas where more bucks survive and grow older, the percentage of yearling bucks drops. Next, biologists determine what percentage of buck deaths are caused by hunting. Last year in unit 77A, biologists estimated that hunters caused 81 percent of all buck deaths.