Counting deer the Tennessee way: infrared technology is helping biologists more accurately figure deer numbers.

ANY HUNTERS question how wildlife biologists calculate deer population figures or buck-to-doe ratios. I can vividly remember when this subject came up for discussion in my first wildlife population dynamics class. I knew what the state numbers were on total number of deer, buck-to-doe and doe-to-fawn ratios and deer per square mile, and I knew what I saw in the woods. To say I was armed and ready to pin down my professor was an understatement.

As a young wildlife student I learned calculating wildlife populations was much more complex than I ever imagined. I also learned that some of the basic techniques used to estimate deer numbers such as track counts and spotlight surveys were quite simple. In fact, anyone with some basic math knowledge could conduct these types of surveys. The problem was you almost never had enough time to cover enough ground or perform replications to make these surveys statistically valid. This all changed within the last 10 years with the invention of trail cameras. Today, with enough trail cameras (say, one per 100 acres) you can accurately determine the number of deer, sex ratio, and age structure of your herd. But what do you do if your area contains thousands of acres? Better yet, what's a wildlife biologist to do across an entire state/province?

Recently, Daryl Ratajczak, Chief of Wildlife for the Tennessee Wildlife Resource Agency (TWRA) used a basic sampling technique for deer using handheld, infrared thermal imagery. Thermal imagery is a technology that projects an invisible infrared beam to "see" thermal energy or heat emitted from an object (deer) during the nighttime hours. Thermal, or infrared energy, is light that is not visible because its wavelength is too long to be detected by the human eye. The beauty of this technology is unlike spotlights, which deer can easily see and avoid, infrared technology is invisible.

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Thus, the deer don't even know they are being viewed. And, just like regular spotlight counts, thermal imagery can be used in the back of any pickup truck to count deer.

Years ago, a study was conducted to compare the accuracy between a regular spotlight and handheld, infrared thermal imagery equipment. The results were significant. Many deer, especially bucks, would simply flee the area or lay flat to the ground, never to be observed with the spotlight. Without the aid of infrared technology, biologists would have never known the bias in using spotlight counts.

With this in mind, Ratajczak was convinced the TWRA could come up with a sampling methodology to be used across an eight-county region in south-central Tennessee. Using 40 randomly selected sections of road (each transect averaged 12.2 miles) from February 1 to March 31 in 2009 and 2010, Ratajczak and the TWRA ran their surveys. The end result was 19.5 deer per square mile in 2009 and 19.1 deer per square mile in 2010. After extrapolating this data across the eight-county region, the total deer population was estimated at around 83,000 deer.

The TWRA also conducted thermal imagery surveys during the summer months prior to the hunting season to determine the sex ratio between adult bucks and does. And, just like they expected, the average was one buck to 1.5 does. The most skewed sex ratio they surveyed was one buck to three does. This was a public area where hunters believed the ratio was more like 10:1, does to bucks.

After these results were made public, a hunter (let's call him "Bob") refused to believe what he was hearing. Since Bob hunted the area all his life, he "knew" the sex ratio and how many deer were in the area. In his personal opinion, and that of many others, the TWRA wasn't even close with their figures. After many back and forth discussions between the various folks, Bob and his faithful followers could not be convinced the state biologists had a better grasp of the deer herd than they did. Instead of engaging in a war of words, Ratajczak invited Bob to accompany him and his crew along on the deer survey. After seeing firsthand all the deer the thermal imagery was picking up, Bob is now one of the TWR As biggest advocates and fully embraces their numbers.

But, let's be honest. Can you relate to Bob? I know I can, and I remember my first radio telemetry project with a collared deer as a college wildlife student. Although I wasn't going to shoot any of our collared deer, the thought of seeing how good an archer I was too tempting to resist. One buck we had collared was a small six-pointer. But he was traveling in a bachelor group with three, bigger bucks. No matter how many times I tried, they always caught me whenever I attempted a stalk, like Bob, I was humbled and now know the states deer biologists are a lot smarter than I ever imagined.

With that said, I know some state biologists rely heavily on harvest data to reconstruct population structures. Granted, the statistics are valid, but they may not be representative of the true, pre-hunt population. For example, more hunters are practicing quality deer management and simply refuse to take small bucks. In this case, can we assume our harvest data accurately reflects what's really in the woods? "This is why I like what Ratajczak and the TWRA are doing with the handheld thermal imagery.

Last year, the TWRA implemented the thermal imagery technique statewide. By comparing deer harvest data with other population indices, along with the thermal imagery, the TWRA hopes to collect even better data on the makeup of the state's deer population.

I have always wondered if deer leave an area after seeing the beam of a hunter's flashlight as he makes his way to a stand in the morning or when leaving at the end of the day. As the outdoor industry strives to improve product quality at an affordable cost, I'm willing to bet that future hunters will be carrying infrared thermal imaging units on their way to and from their stands.

C.J.S' Summary:

Spotlight surveys are a relatively inexpensive method to show trends over time or what we call an index. Although a survey done with infrared thermal imagery costs more, it more accurately estimates the true deer population.

Without a doubt there are a lot of deer out in the field that hunters don't see. Ratajczak shared with me some awesome footage you have to check out at web.me.com/tnwildlife/TN_Wildcast/Thermallmage.html It shows some huge bucks on public hunting areas (where hunters swear up and down there are no bucks at all). In addition to determining the deer per square mile, the TWRA also used thermal imagery (prior to the hunting season) to verify the average adult sex ratio of one buck to 1.5 does on these public hunting areas. By surveying deer at night with thermal imagery cameras, Tennessee biologists are discovering deer no one believed even existed.