How Many Does Should Be Harvested Each Year?

As bow season approaches each year, the most common question I hear as a private consulting biologist is, “How many does should we harvest this year?”

My responses typically come in the form of questions such as, “What is your most recent fawn recruitment rate estimate?” “How many does did you estimate in your carryover data set from last year?” and “Do you estimate your property’s reproductive capacity — based on habitat quality — to be the same as last year, or are there expected changes in either direction?”

What follows is usually a blank stare!

If you want a healthy, more balanced deer herd, don’t wait for your state agency to make it happen. Properly managing whitetails by setting your own harvest prescriptions has never been easier, and most bowhunters already own the tool that makes this feasible: a trail camera!

Trail-Camera Surveys

By conducting a population survey with trail cameras, you can obtain estimates of your standing crop of deer and the reproductive output of your herd. These data points allow you to then harvest the proper number of bucks and does, based on your specific goals and objectives.

In my October column, I’ll show you how to use a simple herd model to account for changes in your annual deer herd based on both additions to (fawn recruitment) and subtractions from (hunter harvest and predation) from your herd. As time goes on, you will then be able to make minor tweaks to your model. Armed with the skills of being able to survey your deer herd and then determine how many deer and which ones you should harvest will allow you to accurately and intimately understand the status of your herd better than your state agency. Before you can develop your own doe-harvest prescription, however, you must conduct your own trail-camera survey.

Employing trail cameras to estimate deer herd characteristics began with research conducted by Mississippi State University and Stephen F. Austin State University. Researchers quickly realized that trail-camera surveys were extremely accurate for determining population size, fawn recruitment, adult sex ratio (buck:doe ratio) and the number of different (AKA “unique”) bucks (buck age structure) that utilize a given property.

Once you obtain these estimates, you’re ready to establish buck and doe harvest quotas based on sound citizen science. Research has shown that a camera density of at least one camera per 100 acres for a survey period of 14 consecutive days results in increased survey accuracy.

Timing Is Critical

How you time your survey is a function of your location in the country (fawning dates), state baiting/feeding regulations and the availability of natural food sources such as hard and soft mast. Fawns must be following their mothers around in order to photograph and count them. For the first 10-12 weeks of a fawn’s life, it spends much of its time in isolation and only interacts with its mother at feeding times. In the Southeast, fawn recruitment rates tend to be more accurate later in the season, since fawning season is drawn out later in the summer months. In fact, fawning in the Southeastern United States can occur from June through July, or later. Many of these late-born fawns are not up and mobile in August. As a result, September and October camera surveys in these regions will result in more accurate fawn recruitment data.

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Although fawns can be more difficult to distinguish from adult does later in the year, postseason fawn recruitment surveys prove more accurate in southern regions. In the northern parts of the country, fawning dates tend to occur during a shorter time period in the spring so fawns can reach a critical body mass before severe winter weather sets in. As result, fawns are generally up and following mom around earlier, allowing for accurate August and September camera surveys.

Site Selection and Attraction

Choose your camera locations based on areas where deer already spend much of their time. The more photographs you obtain, the more accurate your survey will be. Using bait helps draw more deer to your camera stations; however, baiting and feeding regulations vary from state to state. Some states require that all feed is removed a certain number of days prior to hunting season, while others don’t allow feeding at all. Work with what you have to get as many photos as legally possible. If permitted, corn is the optimal bait, but once acorns begin to drop, deer will choose them over corn.

Density and Adult Sex Ratio

Your total density estimate starts by counting every adult deer photographed, including repeat photos. In other words, don’t worry about counting the same deer twice in this step. Since there is no realistic technique to identify individual does, the adjusted total individual doe estimate is obtained by calculating a “population factor” using buck photos. The population factor represents the relationship between the number of individual (“unique”) bucks and the total number of bucks (all buck pictures, including repeat photos) photographed. The ability to distinguish the number of individual or unique bucks to quantify “unique” bucks photographed makes this camera survey technique possible.

For example, if you obtained 950 total buck pictures, including repeat photos, but only 22 of those bucks were “unique” bucks, then your population factor is .023 (22/950). This number, when multiplied by your total number of does photographed, gives you an estimate of the number of “unique” does. For example, if you counted a total of 1,300 doe photographs, including repeat photos of the same does, then your doe estimate would calculate out to 30 “unique” does or .023 x 1,300.

Once you’ve applied the population factor to your doe tally, you can determine your adult sex ratio from the resulting number of bucks and does. In our example, the adult buck:doe ratio would be 22 bucks:30 does. Biologists would simplify this ratio to report the number of adult does for every one adult buck. Using our example, our adult buck:doe ratio is 1:1.36 (30/22 = 1.36 does for every one buck).

Buck Age Structure

To determine your buck age structure, or the percentage of bucks you have in each age class, each buck is assigned an age estimate. You can then determine what percentage of your buck population is composed of yearlings (1.5 years), 2.5- and 3.5-year-old plus deer. If large-racked bucks are your goal, harvest guidelines will be developed around increasing the percentage of 3.5-year-old and older bucks.

Your resulting data will allow you to be armed with your total estimated deer density, total number of fawns added (50 percent are buck fawns), total number of adult bucks, total number of adult does, adult sex ratio and estimated buck age structure. These are the figures I will teach you to plug into a basic herd model in my next column. The resulting numbers will assist you with prescribing doe harvests and more!

Learning More

I’ve introduced the main aspects of running a trail-camera survey, but due to a lack of space, I will also direct you to a fantastic publication from the Mississippi State University Extension for more details on conducting your own camera survey: extension.msstate.edu/sites/default/files/publications//p2788.pdf

As you refine your skill set as a citizen scientist, you will no longer have to wonder how many does you need to harvest this season, or how many pipeline bucks you can expect to carry over from previous years. In fact, my clients often report that their regional biologist is impressed with their in-depth understanding of the productive potential of their deer herd and habitat.