Idaho Fish and Game biologists have spent decades counting and monitoring deer and elk populations including when, where, and how animals die. It’s a critical part of understanding all facets of wildlife management, and a common question is often, “what kills the most deer and elk?”
The short answer is hunters kill the most bucks and bulls, and that’s by design.
“That’s the whole point of managed hunting and harvest,” Fish and Game State Wildlife Manager Rick Ward said. “Regulated hunting should be the highest cause of mortality, at least for bucks and bulls, we want hunters to get them before something else does.”
But not only bucks and bulls die every year. The information biologists have collected on causes of death provides a fascinating glimpse into what happens to deer and elk when it’s not hunting season, and how biologists factor that information into their management decisions.
Much of Fish and Game's work on documenting mortality in Idaho has centered around mule deer. For more than 20 years, crews have gone out every winter and captured and radio-collared does, fawns and bucks to find out how many survive and what killed the ones that didn’t.
Biologists pay close attention to the survival rate of mule deer fawns because they’re most vulnerable during their first winter, and roughly half of them die in an average winter.
Wildlife managers know there’s a direct link between the severity of winter and fawn survival. Monitoring survival provides an early signal that hunting season changes may be needed in the future. They also know a string of mild or moderate winters can allow herds to grow quickly.
Wildlife managers have expanded collaring to include elk and whitetails, including new-born fawns and calves, as well as some predators, to learn more about the overall population dynamics of deer and elk in different habitat and landscapes throughout Idaho.
As a rule of thumb, the health and abundance of the adult does and cows is the primary factor that determines whether the herd stays stable, grows or declines.
The reason for that is fairly simple. It takes a relatively small percentage of adult bucks and bulls to breed all the females within the herd. Adult females typically survive at high enough rates annually that if a major die-off of young occurs, there will still be enough adult females to produce the next generation and grow the herd when conditions improves.