Blue Tongue Disease in Deer: How is it Affecting Populations?
June 18, 2013
EHD, also known as epizootic hemorrhagic disease or blue tongue, swept across the whitetail range like a plague during the summer and fall of 2012, killing untold numbers of whitetails. Briefly, EHD is a virus that is transmitted from deer to deer by small biting flies known as midges. EHD spreads more quickly during bad droughts — such as that experienced across much of the nation last summer — because deer come to water more often as they don't get much moisture from the vegetation they consume. The exposed mud around the water sources is the breeding grounds for the midges. So, when deer come to a get a drink, they are at very high risk for being bitten by the bugs and "injected" with the virus.
Deer herds from Florida to Montana were impacted by EHD. Mortality rates varied widely from region to region and even locally within each region. In some areas, EHD's impact was insignificant, while in other areas entire herds were virtually wiped out by the disease. In the hardest-hit areas, wildlife officials were forced to take the unusual step of altering hunting seasons and/or decreasing the number of available deer permits available to hunters. For example, Nebraska Game and Parks has significantly reduced the number of deer permits for the 2013 season due to the mortality caused by EHD during 2012.
On my property in southwestern Missouri, the deer herd was significantly impacted by EHD. My wife Tracy and her dog Crystal really enjoy shed hunting. Unfortunately, they found way more skulls than sheds last winter. They also found the skeletons of several does and young bucks. The results of this EHD outbreak will impact my family's hunting during the 2013 deer season and for many more years to come.
There are still deer at my farm, including some mature bucks. But I have several questions: How many deer are present? How many mature bucks survived the EHD outbreak? How many does and fawns survived? As a biologist, I realize does (reproductive units) and fawns can be replaced relatively rapidly. However, there's a long waiting period to replace mature bucks.
At my farm, I classify bucks as mature if they are 4 years old or older. So, simply going through the math, it will require five growing seasons to replace a 4-year-old buck. Thus, a 4-year-old buck that died during 2012 won't be replaced until 2017. The replacement buck will be born during the spring of 2013 and be a button buck or approximately six months old during the fall of 2013. He'll be 1'‰½ years old during the fall of 2014, 2'‰½ during the fall of 2015, 3'‰½ during the fall of 2016 and 4'‰½ during the fall of 2017.
Certainly, there are some mature and immature bucks that survived the EHD outbreak. To get an accurate estimate of how many bucks survived, and their age structure, I'll do a trail-camera survey during August. Camera surveys are an accurate way to determine the number of bucks, does and fawns on a property. Research by Dr. Harry Jacobson and Dr. James Kroll has shown the camera-survey technique to be more than 90 percent accurate. That's amazingly accurate for counting wild, free-ranging deer. Camera surveys do a much better job of estimating the population than spotlight counts, track counts, pellet counts or other methods. Camera surveys have other benefits as well, such as providing the buck-to-doe ratio, number of mature bucks, size of mature bucks, number of fawns surviving, etc. In addition, who doesn't like getting pictures of mature bucks where they will be hunting in a month or two?
The camera-survey technique is based on using grain and/or minerals to attract deer to a camera site. This technique works best when food is scarce, like during August. During most years, this is the time vegetation is maturing, dry or otherwise decreasing in palatability. Deer respond rapidly to supplemental feed and/or minerals under these conditions.
Antlers are used to uniquely identify bucks — like fingerprints for humans. Typically, the camera sites are pre-baited for about 10 days; then the survey begins. This allows all the deer in the area to be conditioned to visit the camera site. Then the number of individual bucks is counted, and the total number of times each bucks is photographed during a 14-day survey period is recorded.
This data allows the total number of unique bucks and the average number of times a buck visited the camera site during the survey to be calculated. Using this information, the total number of doe and fawn pictures are counted and then divided by the average number of times bucks visited the camera sites during that survey. These simple calculations provide accurate estimates of the total number of bucks, does and fawns on a property during the camera survey.
In addition, the pictures from a camera survey allow me to estimate the age and antler size of each buck using the property! Using this information, I can formulate harvest guidelines for my family and our guests. I can accurately create a "hit list," and just as importantly, show guests the bucks I'd prefer they pass and allow to mature.
Camera surveys are a great tool for managing and hunting whitetails. As you prepare for the upcoming archery season, I encourage you to maximize the benefits of your trail cameras as a tool to become a better deer hunter and a better deer manager.