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The Myth About Pre-Season Sex Ratios

How many times have you heard a buddy talking about the high number of does seen on his hunting territory? “I only see one buck for every ten does. There are just no bucks left here. Why doesn’t the game department do something?”

I’m not saying those hunters are fabricating what they perceive. Most probably believe that there are 10 adult does for every buck in their hunting woods — but is that really the case? Let’s consider this situation, and see just what gives hunters the impression that the preseason doe-to-buck ratio is out of whack.

By the way, it is more than the average hunter that has this impression. I’ve met biologists, outdoor writers and others who also believe that doe-to-buck ratios can be very high. I’ve read stories written by well-known outdoor writers talking about high doe-to-buck numbers they’ve seen while hunting, and they write about it in such a way that readers are left with the impression that there really are 10 does out there for every adult buck. The truth is, though, that science doesn’t support these contentions. It is extremely rare and in fact nearly impossible for such sex ratios to exist before the hunting season. Here’s why.

It might seem obvious, but there is no question bucks are more wary than does. This is true before the hunting season and even more true once the bucks get shot at. Thus, timing is definitely a factor when considering sex ratios. Go out the last week of the buck gun season and you will see a lot more adult does than adult bucks, and it has little to do with the preseason sex ratio. For one, the bucks are more wary, and many bucks have been harvested. In many states the biggest percentage of bucks are harvested the first two days of the season. Go out later and you just might get the impression that the sex ratio is way out of whack.

Another possible factor here is counting fawns as does. When a herd of deer run by, a fawn could get counted as an adult doe rather easily. This helps give the impression that the sex ratio is 10:1. In reality the sex ratio could be 2:1, but considering all the above, the hunter’s impression might be wrong. Several scientific studies show that hunter observations are not representative of the ratio of does to bucks that are in the woods. Don’t get me wrong — I agree that in almost all situations we have more adult does than adult bucks. However, what the science shows is that it isn’t as out of kilter as we think.

Let’s focus on the sex ratio right before hunting season. Kip Adams of the Quality Deer Management Association (QDMA) has examined the various factors that affect the sex ratio. He outlines a hypothetical situation that demonstrates that the biological maximum you can get, even when no does are harvested, is 5:1. Remember, the sex ratio of newborn fawns is about 1:1, so that is a built-in annual correction. If for some reason the mortality of fawns is very high, then down the road that will affect the sex ratio, because you won’t get the 1:1 sex ratio correction that fawns give you each and every year.

Doe mortality is another factor that affects the sex ratio. Of course hunting seasons take a lot of does, but Adams notes that an additional 15 to 20 percent of adult does die from predators, cars, disease, etc. each year. In fact, in the website cited above, Adams provides an example where 90 percent of the bucks are harvested, and no does are harvested. You would think that not harvesting any does would lead to a high doe-to-buck ratio, but it doesn’t. The reason is that after the hunting season few bucks will die, but 15 to 20 percent of the does will die from natural mortality. Add in the fawns from last year, half of which are bucks, and that supposed 10:1 sex ratio plummets to 3:1. Adams has more data here, but the bottom line is that you just cannot end up with a high doe-to-buck ratio. Other studies show that you tend to have lower sex ratios when the overall deer density is low, and you tend to have higher doe-to-buck ratios when the population is high. One recent study shows that you need to move bucks into older age classes to reduce the adult sex ratio. More older bucks are a key. Without that, and the sex ratios will probably remain out of whack.

To summarize, science shows that sex ratios might be a bit high in favor of does, but they aren’t as high as we sometimes think. Now to the neat part of this discussion. Hunters want a deer herd that is managed properly. When this is done, you should have a doe to buck sex ratio that is less than two adult does per adult buck. Going into the hunting season, that ratio is an important indicator of a healthy deer herd. There are other factors that help guarantee a healthy herd, but a balanced sex ratio is critical. Why?

Because it gives you more exciting hunting. How so? A balanced adult sex ratio compacts the rut and makes it more intense over a shorter number of days. Lots of does per buck means that all does don’t get bred in the first rut cycle. Some get bred around a month later. More importantly, the bucks do not have to work very hard to find a hot doe. Hot does are numerous, so the bucks just run into a hot doe trail and follow it. No need to go to scrapes, or make scrapes. No need to compete with other bucks for the hot does. There are plenty. Additionally, more breeding will probably be done by the less competent yearlings, because there are lots of does.

All this means is that rattling won’t work as well. Hunting near scrapes won’t work as well. Grunting at rutting bucks won’t work as well. Yep, the truth is that skewed sex ratios take the punch out of hunting the rut. Tightening up that sex ratio and increasing the age structure of the bucks makes hunting a whole lot more fun. Just look at what has happened in recent years near my home in western Pennsylvania. Those hunters are having more fun and seeing more and bigger bucks than ever, and a lot of this is because they implemented a management strategy where the doe harvest was increased and antler restrictions started moving bucks into older age classes. These regulations brought the sex ratio closer to 1:1, and made the rut more competitive. We have more older bucks and fewer does. Calling deer, rattling deer, hunting near scrapes, etc. all picked up. Like I said, hunting became more fun, and hunters also started seeing and killing bigger bucks.

Research also shows that you get a higher percentage of yearling bucks dispersing in the fall when you have a higher proportion of adult does. From a numbers perspective, that’s not really a problem if someone else’s yearling bucks are dispersing to your property. But if you’ve invested in creating quality habitat by managing your timber and building food plots, then your yearling bucks probably have better antlers and body weight than your neighbors, and 70 percent of them are leaving your property. Someone else’s lesser-quality yearlings are then coming to your place. That isn’t a good trade-off. When preseason sex ratios are below 2:1, fewer yearling bucks disperse.

There are things you can do on your property to affect adult sex ratios. First, you need to get an idea of what is out there so you can adjust your doe and buck harvest. August spotlight counts (where legal) can give you some idea of the sex ratios you have. You can also use cameras to estimate your deer sex ratio. If you Google “accuracy of the camera technique for estimating white-tailed deer population characteristics” you will get the entire paper that covers how to best do this.

There you have it. Equal adult sex ratios makes hunting a lot more exciting. As for those preseason adult sex ratios of 10 does for each buck — those are a myth.

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