Wildlife biologists who work for state wildlife agencies often use buck-to-doe ratios to better understand deer populations and determine harvest quotas for hunters.
You might wonder, “What’s a buck-to-doe ratio?” To help explain, we spoke with Charlie Killmaster, a deer biologist with the Georgia Department of Natural Resources.
A buck-to-doe ratio, aka the sex ratio, is the number of adult does for each adult buck in the area’s deer herd. Although it’s called a buck-to-doe ratio, the doe tally is usually listed first, as this article in Petersen’s Bowhunting notes. For example, if a sex ratio is 3:1, it means the herd has three does for each buck.
Sex ratios are determined various ways, including field research, trail-camera surveys, and data from hunter observations. These ratios are often based on the herd’s pre-hunt population because hunters often target bucks more intensely, skewing post-hunt populations toward does and fawns. Biologists in some areas also omit fawns when calculating sex ratios because half of the fawns are antlerless males, often called “nubbins” or “button bucks.” Buck fawns shouldn’t be included in the doe calculation because they would skew the ratios.
Killmaster said ideal buck-to-doe ratios are roughly 1:1, given reasonable harvests and nonhunting mortality. However, few areas achieve such balance. Ratios usually skew higher toward does, and can vary by region and even individual property.
Heavily skewed sex ratios can affect breeding activity, the health of individual deer, and the health of a herd and its habitat.
For example, a ratio skewed toward does can cause long, less-intense ruts. Unbred does will enter estrus a second time, and bucks – driven as they are to reproduce – will continually push themselves to breed every estrous doe. Those efforts physically exhaust bucks, which can leave them vulnerable to disease and predation.
A herd with overly abundant does can also make bucks less competitive because they seldom have to fight for dominance and breeding rights. That can increase the possibility of less-intense, drawn-out ruts.
Killmaster said an extended breeding period also expands the spring fawning window, which can increase fawn predation. Bears, bobcats and coyotes can only find and kill so many fawns if they’re all born at the same time, a process called “swamping.” Fawns are most vulnerable to predation during their first month, when they’re unable to outrun most predators. The more fawns there are on the landscape, the greater their individual odds of escaping notice while most vulnerable.
If fawns drop at different times over a long period, predation opportunities increase. In addition, fawns born in summer in Northern states likely won’t be mature enough by winter to survive brutal cold and deep snow.
And here’s yet another challenge if sex ratios skew toward does: It can quickly cause overpopulation and overbrowsed habitat. Biologists then must find ways to reduce the herd, which usually means increasing antlerless quotas and bag limits and, ultimately, issuing far more antlerless tags than buck tags.
To do their part for conservation and ecosystem management, hunters must abide by these harvest guidelines and regulations as they pursue deer.
Killmaster recommends hunters work closely with biologists to determine the deer herd’s sex ratio on their property, and agree on a goal. In turn, that goal will help determine how many does to harvest each fall.
After that, hunt hard to keep the herd at those goals, and work with conservation wardens by reporting poachers in your area. Also check out the article “Why Is It ‘Only a Doe?’” at Bowhunting 360 to learn more benefits of doe harvests. Hint: They can improve your odds of harvesting big bucks.