Buckmasters Magazine

Understanding buck-to-doe ratios is not as simple as you might think.

As the deer project coordinator for the Virginia Department of Game and Inland Fisheries, Matt Knox fields a lot of calls from his constituents. A common conversation revolves around a disproportionately high number of does observed to the number of bucks. At least that’s what many of the hunters he talks to say.

THE FAWN FACTOR

“They see a whole lot of antlerless deer and just a few bucks, so they automatically assume the buck-to-doe ratio is way out of whack,” Knox said.

What many hunters don’t consider, however, is that a deer without antlers might very well be a buck. Remember, whitetails don’t produce a set of antlers their first year. Just because it’s not sporting a crown on its head doesn’t mean a deer is not a buck. Fawns come in both flavors.

If, for example, a hunter counts 20 deer in a field and only four have antlers, he automatically assumes the doe-to-buck ratio is 16:4, or four does for every buck. What he’s really seeing, says Knox, is 16 antlerless deer to four antlered deer. He’s not considering the number of fawns in that group.

“Let’s use a typical population where a doe will bear one fawn,” he explained. “For every adult doe in that group, there is one fawn. Of the 16 antlerless deer, eight will be fawns and four of those fawns will be bucks. Of course, not all fawns survive, but it’s fair to assume that mortality rates are equal for male fawns and female fawns, so the number of each in the population will be equal. Assuming zero fawn mortality, that gives you a total of eight bucks and 12 does for a ratio of 1 to 1.5.”

Something many hunters find difficult to wrap their heads around is how each year’s new fawn crop makes it impossible to have a doe-to-buck ratio of more than 2.5 to 1. That’s because out of 100 fawns, 50 are likely males. No matter how many antlered bucks are removed from the population, half of the new deer coming into the population will be male.

The catch relates to how many fawns are added to the population each spring. In typical habitat, one doe accounts for one fawn, although does can produce three fawns at a time in areas with really good habitat. In poor habitat or areas with an overpopulation – which ultimately has a negative impact on the habitat – fawn production can decrease. Heavy coyote predation also can impact recruitment rates. When fawn recruitment drops significantly, a high antlered buck harvest can result in a skewed ratio with an overabundance of adult does.

Biologically Speaking

That’s not necessarily bad, at least from a biological perspective. You might not see as many bucks during hunting season, but what matters most is the total number of deer on the landscape. Too many can damage the habitat, which can have long-term impact on overall herd health. However, a buck and a doe of equal weight and health eat the same amount of food.

WORST-CASE SCENARIO

Having a high number of breeding-age does can result in an unnatural breeding cycle, however. Remember, does come into heat monthly until they are bred. If there are too many adult does, they might not all get bred during the first rut. That can result in a second or even a third rut. Since the gestation period for a whitetail is about six to seven months, that means some fawns can be born as late as July. Late fawns typically have lower survival rates and smaller antlers for their first several years.

Low survival rates aren’t necessarily an issue in the South. In fact, peak breeding dates in some regions of Florida are as late as mid-February. In parts of Alabama, Louisiana and Mississippi, does are bred well after New Year’s Day.

Knox can’t say what sex ratio would result in a dramatic shift in fawn birth dates, but he says there are few examples of that actually taking place. No state is a better illustration than Pennsylvania, where hunters were prohibited from shooting a doe and were limited to one buck per season throughout much of the state’s modern history. The Game Commission revised the deer regulations in 2002 to increase the doe harvest and alter the buck age structure through antler point restrictions.

“There has been some really great reproductive data collected since the deer season structure was changed,” Knox said. “Basically, reproduction wasn’t influenced at all by the decrease in adult does and the increase in breeding-age bucks. Does are being bred and fawns are being born at the same time as they were prior to the regulation changes.”

THE ADULT FACTOR

If sex ratios have little influence on breeding ecology and biology, why do so many hunters and managers get hung up on them? There’s no question hunters like seeing antlers, no matter what size they are. What’s more, a closer buck-to-doe ratio results in more active breeding behavior. Bucks spend more time cruising for does and more time chasing – the things hunters hope to see during the rut. Who doesn’t enjoy a good chase?

But if a steady supply of fawns prevents the buck-to-doe ratio from getting too far out of whack, can we influence the adult sex ratio through excessive harvest of one particular sex?

Of course, agree Knox and Texas A&M-Kingsville research scientist Dr. Charles DeYoung, who has seen post-hunting-season adult doe-to-buck ratios as high as 7 to 1. Such a scenario is the result of excessively high adult buck mortality.

Adult males have a higher mortality rate, even in unhunted populations. With added mortality from hunting, the rate goes even higher. It only makes sense that shooting lots of bucks and few adult does would result in an unbalanced sex ratio.

Just how much buck mortality does it take to skew ratios? Knox and fellow biologist Pat Keyser co-authored a study that examined sex ratios under various rates of mortality for bucks and does. They used computer models to simulate mortality rates of 80, 60, 35 and 30 percent for adult bucks and 20 and 40 percent for adult does.

Abnormally high harvest rates for bucks and low harvest rates for adult does did result in a grossly unbalanced herd. For instance, an 80 percent mortality rate for adult bucks combined with a 20 percent mortality rate for adult does resulted in a ratio of about one buck per three does. A 30 percent buck mortality combined with a 40 percent doe mortality produced a relatively even ratio.

It doesn’t take a computer model to figure that out, though. Knox says areas with exceptionally low doe harvests and high buck harvests can have sex ratios way out of balance. It’s not out of the question on a local level, but such high doe-to-buck ratios are extremely rare on a statewide level these days. Few places have an annual buck harvest of 80 percent or even 60 percent. A long-running survey of Virginia bowhunters found the statewide sex ratio was about 2.5 does per adult buck.

“Biologists have done a good job of manipulating population dynamics through bag limits and seasons,” Knox said. “Pennsylvania used to be the poster child for really bad buck-to-doe ratios, but after they increased the doe kill and went to antler point restrictions, the ratio is right in line with most other states.”

Ironically, Knox has skewed sex ratios on a property he hunts, but they would make any deer hunter envious. He’s got more bucks than does. In fact, the first nine adult deer he saw during a recent early muzzleloader season were antlered bucks. Knox didn’t shoot a single one.

“We might shoot a buck every other year between us,” he said. “I haven’t shot a buck off that property in 30 years. We’ll shoot about a dozen does per season, though.

SHOOT MORE DOES?

Many hunters assume an abnormally high number of does means one simple solution: Shoot more does. Even with liberal antlerless bag limits in many states, it’s still a hard pill for many to swallow.

The allure of antlers is simply too powerful, even if those antlers are just spikes no thicker than a pinky. Many hunters practice trigger restraint and sound management, but their neighbors don’t. A high buck harvest on surrounding lands can cancel your best efforts.

Shooting more does isn’t always the correct solution, either. DeYoung recalls a ranch that had seven adult does for every adult buck. The owner automatically assumed the best management method was to dramatically increase the doe harvest.

“The problem wasn’t a lack of doe harvest,” DeYoung said. “After evaluating his herd, we determined that he had a pretty low deer density. It was something like one deer per 70 acres. He was shooting too many bucks. We recommended that he shoot fewer bucks and no does to allow the does to boost the population. A couple of good fawn crops can dilute an uneven ratio and even it out.”

In other words, if you are certain you have a high ratio of adult does, don’t assume your best option is to shoot more adult does. Knox’s model found increasing the doe harvest had little long-term improvement in sex ratios in some populations.

He and Keyser did determine that does are the biggest factor driving sex ratios because they produce future bucks. Because most hunters don’t have the ability to accurately determine sex ratios or undertake precise and correct management practices, it’s best to err on the safe side. Shoot fewer bucks and you’ll have more bucks on your land.

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