April 22, 2014
A study by University of Wisconsin-Madison scientists suggests the best way of stemming the spread of chronic wasting disease among whitetail deer is to kill more bucks, which are most likely to carry CWD and spread the disease among the species.
CWD, a transmissible neurological disease of deer and elk that produces small lesions in brains of infected animals, can quickly spread from one area to the next as deer, particularly bucks, move. The study, released March 21, suggests the disease can be reduced if hunters target its most likely carriers.
The study was led Dr. Christopher S. Jennelle and Professor Michael D. Smith, both of Wisconsin-Madison. Jennelle, Samuel and their research team studied deer-harvest data from Wisconsin’s 2002-2013 hunting seasons, evaluating rates of CWD infection and analyzing how alternative management plans would affect CWD and the herd.
The 12 years of data showed CWD infection rates are twice as high in males as females and support the idea that the rate at which deer become infected is driven by CWD prevalence in the herd, not the size of the herd.
“Frequency-dependent diseases are typically hard to control with generalized removal strategies,” Samuel told Wisconsin Outdoor News. “If male and female deer had the same disease prevalence, the only way to reduce prevalence would be to selectively remove more infected animals than uninfected animals. We’d have to capture deer and test them, which would be very difficult and costly.
“Because we can easily distinguish bucks (by their antlers) from females, we’re lucky to have a management option.”
By increasing the buck harvest, the study suggests, it would reduce the number of deer dispersing from a CWD area to what would be considered a non-CWD area.
“Shooting more bucks to reduce prevalence is one key to managing this disease, but we still need to work on abundance to some extent,” Samuel said. “These things go hand in hand.”Researchers wrote that under the current management practices in Wisconsin, 50 percent of the bucks and 25-30 percent of the does in the state could be infected within the decade.
”These are sobering options, but the sooner we act, the less severe the problems and choices we’ll face,” Samuel said. “If we don’t do anything and just stick with what we’re now doing, we’ll lose more adult males because we’ll get such high infection rates.”
However, there is a catch, according to Jeremy Flinn, the Midwest regional wildlife biologist for Cabela’s. Balance must be achieved in order to have a healthy herd, he said.
“The more bucks you move out of a herd, if you’re not adequately removing the number of does out of the herd to balance it, now you’re skewing the adult sex ratio,” Flinn said.
Without that balance, rut activity lessens as bucks don’t have to work as hard to find does in estrus. As a result, fawns are born later, not the best time for survival and growth.
“The fawn is not dropping at the optimum time as the doe is not able to take in the best quality nutrition and pass it to the fawn,” Flinn said. “At the same time, the fawn has less time to grow and prepare itself for winter, especially in northern states.”
Another factor is the fawn population’s increased vulnerability to predators.
“Let’s say all of the fawns are born in a three-week period. Well, there’s only so many fawns predators can eat,” Flinn said. “When they’re all born in that tight time frame, a lot of them make it to an age where they can escape predation and survive. When you spread that out, there’s a few fawns born this week, a few the next week, a few after that -- and predators can stay on top of the fawns being born.”
Flinn went on to say that at least on the state level, biologists are mostly in agreement with the study in terms of preserving the natural resource of a statewide deer herd. But as far as a private herd and a land owner’s desire to create an older buck structure and potentially balance the doe-to-buck ratio, there is disagreement.
“So do you look on it on the short term of how I’m improving the property and improving on a small scale? Or is this going to protect the natural resource on a whole?” Flinn said. “If the latter is the case, I would say most biologists would be for it.
“However, this is just based on the fact that we know deer disperse, that males will disperse more than females and so in theory, if we reduce the number of bucks in the population, we will reduce CWD. For most biologists, that’s not going to be enough to say, let’s shoot more bucks.”
As CWD becomes more prevalent in the Midwest, Samuel said, more plans and solutions are needed.“The sooner we actually do something about CWD, the better off we’ll be,” Samuel said. “We still don’t know how the disease spreads, but one likely way is by infected yearling bucks dispersing to new areas. The worse the disease prevalence, the higher the infection rate we’ll see in young bucks, and the more likely they’ll spread the disease.”