Deer Density, Buck to Doe Ratio, and Harvest Rates

A couple of weeks ago, I wrote about the impacts of habitat quantity and quality on white-tailed deer harvest rates. Habitat quantity does not necessarily impact the harvest rate itself, but a property that provides a smaller amount of habitat must harvest fewer deer than a property that provides a larger amount of habitat in order to keep the deer population on the ranch stable. Habitat quality, however, can vary between properties that provide the same quantity (in acreage) of deer habitat, which in turn impacts the health and productivity of the ranch’s deer population.

Habitat quality impacts deer harvest rates because herd productivity will vary between properties. If deer density is held constant, deer on a property that provides good habitat will be in better condition than deer on poor habitat. This superior body condition can be measured through increased body weights in animals and improved antler quality in every age class of bucks. Today, I will discuss how fawn survival, as effected by deer density and the buck to doe ratio, can significantly impact the annual harvest of white-tailed deer populations.

Most hunters understand that fawn production is an important component of white-tailed deer management, but they fail to realize how annual fawn survival directly impacts the number of deer harvested each year. Fawn production (the number of fawns born) is difficult to measure, but fawn survival is not. A good estimate of fawn survival can be collected annually using daylight surveys for whitetail deer in late summer and early fall.

Every hunter wants to see bucks—and we all know they start as fawns—but once a property reaches its ideal carrying capacity, proper deer density, and buck to doe ratio, then it is fawn survival that ultimately determines the number of deer that should be harvested each year. A year with low fawn survival will not add many animals to the population, so not many adult bucks and does should be harvested. On the other hand, a year with high fawn surival means many new animals have been added into the population, so hunters must remove deer to maintain the property’s deer population at the proper deer density.

A healthy deer population will more productive than a stressed deer population. As a result, reproductive success, as measured through fawn survival, can be a good measure of the health of the local deer herd. In turn, good reproductive success is often reflective of good deer habitat. Habitat conditions will vary annually based on precipitation, but white-tailed deer found on good habitat will almost always have higher fawn survival than deer found on poor habitat, regardless of the year. And all this stems from habitat quality, which determines the condition of individual deer living on the ranch. Healthy does produce more fawns and healthy fawns have higher survival rates. It really is the cycle of life.

Many hunters fail to realize that fawn production is strongly tied to habitat quality and the body condition of individual deer. Case in point: Think about a property that has a good number of deer, but the number of bucks is relatively low. The guy managing the property thinks that not shooting does will eventually lead to more bucks. But it doesn’t work. What’s going wrong? Well, a bunch of unhealthy deer on poor habitat will not produce many fawns.

The typical problem that exist on properties such as in the example above are that there are simply too many deer! If a property can only support 50 deer and there are 100, then fawn survival will be low. It wouldn’t matter if the buck to doe ratio was 1:1 or 1:5, if there are too many deer fawn survival will be low. The proper remedy in the example above would be to remove a good number of the does so that the remaining does could raise fawns, thus leading to higher fawn survival. A 10% (4) fawn survival out of 40 does is less deer than a 60% (12)fawn survival out of 20 does! That also means 6 new buck fawns instead of only 4. This is just a simple example, but you get the idea.

High fawn survival rates are great, but they also lead to the need for high deer harvest rates. This is why healthy deer herds maintain a low buck to doe ratio. Time for another example: Let’s say a ranch can support 100 healthy deer and the buck to doe ratio is 1:5, or 20 bucks and 80 does. A modest 50% fawn crop means that 20 buck fawns and 20 doe fawns will be produced. To maintain the population at a healthy density this means 20 bucks and 20 does must be removed during the hunting season—but there are only 20 adult bucks! If the buck to doe ratio was brought down to 1:1 then a modest 50% fawn crop would mean that 50 does would have 25 fawns, or approximately 12 buck and 12 doe fawns. The addition of these animals into the population would warrant shooting 12 bucks and 12 does. Luckily, there are 50 adult bucks and adult does to choose from. The hunters could harvest 12 bucks and still have a good age structure in the buck population.

Hopefully, understanding the dynamics of a deer population will help you identify each of these factors on your property and help you reach your white-tailed deer management objectives.The annual harvest rate of white-tailed deer on any property is determined by deer density, habitat condition, the buck to doe ratio, and fawn survival. Factors that impact the body condition of individual deer will impact the dynamics of the population as a whole. Good habitat will lead to higher fawn production and the need for a higher deer harvest rate, but managers can mitigate excessive production by manipulating the buck to doe ratio.