Understanding Why Deer Populations Are Increasing in the US

After discussing what happens when deer over-populate an area and starve to death, die of illnesses such as CWD or die due to an increase in car vs deer collisions, people might wonder about how deer populations are increasing catastrophically in so many areas in the US and why hunting pressure isn’t keeping the population in check.

In the US, there are primarily two species of deer, not counting elk (wapiti) and moose, which are both species of deer. There are white-tailed deer and mule deer, and each has subspecies. The two also interbreed in areas where the populations overlap and there is roughly the same number of both species.

Just counting white-tailed deer, it is estimated that in 1930, the population in the US was around 300,000. Today, around 90 years later, the estimates are above 30 million white-tailed deer. Why hasn’t hunting kept the numbers from exploding?

For many decades, the only deer that could legally be hunted were the bucks or males. This doesn’t really slow down the population increases. This is because a buck will typically breed with 10-15 does or females. If a buck is removed, another buck simply breeds with those does. Each of the does then goes on to give birth to 1, 2, or rarely 3 fawns. Twins are common. This also occurs every year.

Looking at it from a numbers perspective, suppose for a moment that in a herd of 30 deer, half of them are bucks and the other half are does. There are actually more than 50% that are does, but for this example, we’ll say that the herd has 15 does capable of having offspring.

Let’s say that in a particular year, 5 bucks are taken. Again, in actuality, far fewer bucks are taken than this, but it allows us to see what happens.

Through hunting, this drops the number of deer in the herd to 25. However, there are still 15 does and all of them get bred by the remaining bucks. If each one of them gives birth to only a single fawn, that is an increase of 15 deer. The average is for does to have twins, but we are purposely giving the most conservative numbers.

The herd dropped in number to only 25 from the harvest of 5 bucks. However, it gains another 15 deer, so the number is now 40 deer. The herd has grown by 33% in one year, and if half of those fawns are females, these will become breeders the following year. Even counting the does that die from predation, in car accidents, and so forth, the size of the herd is still increasing, with more does to give birth. 

In reality, fewer than 5 bucks are taken per herd, per year, which would be a third of the bucks. Further, there are more does than bucks. Additionally, most does have twins and not single fawns. It isn’t difficult to see that the herds are really growing by more than 33% per year, by just hunting bucks.

Many states have finally figured all of this out and also have a limited doe hunt now. It might be too little, too late. In Montana, which does have a limited doe hunting season, the average number of deer that are harvested each year is around 4,000. That is both bucks and does. And yet, the deer population in Montana increased by 40,000 between 2007 and 2017. That is an increase of 4,000 deer per year, despite the number that is taken. Without the deer hunting, the deer population would increase by 8,000 per year.

This is more than bad for the deer, it can also be deadly to people. A couple of hundred deer are hit and killed by cars yearly. Hitting a deer at 70 mph does kill the deer. It also mangles the car and often results in human fatalities and tremendous property damage.

Clearly, we need more hunting, not less.