The Three-Minute Outdoorsman: Wild Science from Magnetic Deer to Mumbling Carp

13. Mountain Lions, Prions, and Sick Deer

t h e t h r e e - m i n u t e o u t d o o r s m a n 60 positive outcome by some but not by others. The Wisconsin DNR seems to have done a good job of balancing both. Perhaps the message to deer hunters is that if you don’t want an EAB in your area, harvest does when the DNR requests you to do so. 13 mountain lions, prions, and sick deer Chronic Wasting Disease (CWD) is a neurological disease that produces small lesions in brains of deer (white-tailed, mule), moose, and elk. Infected animals are in poor body condition, exhibit behavioral abnormalities, and later die. Infected deer apparently do not recover from CWD, but studies suggest that some deer may have a genetically based partial resistance (see earlier chapter on CWD). The disease is similar to scrapie in sheep and mad cow disease in cattle. Most diseases we are familiar with are caused by bacteria or viruses, but CWD is likely caused by a naturally occurring protein that for a mysterious reason becomes misfolded and is then called a prion, which is infectious and can destroy its host. Prions build up in nerve tissue, causing the death of nerve cells and loss of normal body functions. Confirmation of CWD is obtained by examining the brain tissue from a dead animal under a microscope and finding spaces (holes). Attention to CWD waxes and wanes in the popular press depending on the occurrence of outbreaks or new findings of spread. Nonetheless there is still considerable scientific interest in this disease and in understanding its ecology and effects on deer (and elk and moose) populations. The cause for the attention given to CWD is at least twofold. First, it can severely affect a deer or elk population, and deer hunting is a hallowed pastime as well as a major economic factor. Second is the possibility that the disease can be transferred to humans who consume infected deer. Because CWD is like mad cow disease, it garners our attention. A L L T H I N G S D E E R 61 However, the Centers for Disease Control found no evidence that the disease has ever crossed the “species barrier” and infected humans. Still, we are advised against eating infected deer, cutting through bone, and eating certain organs, like brain and spinal cord, that seem to harbor the highest concentrations of prions. So, that brings me to the actual point. Animals in the wild get sick. And we all know that in an ideal world, predators, such as mountain lions, preferentially kill the sick and the old, thereby keeping the herd healthy (the so-called sanitation effect). Actually , I doubt that a mountain lion would pass up an easy kill on a healthy deer. But not a lot of evidence exists that confirms that such predators preferentially take out the old and the sick, like those with CWD—it just sounds reasonable. A recent paper on mountain lion predation on mule deer suggested that maybe predators behave like we think they should. How the information was obtained is pretty cool. As anyone who has spent time outdoors knows, locating a lot of mountain lions, observing them kill a lot of deer, and then figuring out if the lions were preferentially killing sick and old deer are not easy tasks. But in the mountains of the northern Front Range in Colorado, Caroline Krumm and her colleagues did the next best thing (Biology Letters 6: 209–11 [2010]). They captured nine mountain lions and fitted them with GPS collars. Then, they looked at the GPS coordinates transmitted from the collars and predicted that a cluster of locations was where the lion had made a kill. They went out and found the kill, and if it was a mule deer, they took samples to determine if it had CWD. Talk about armchair biology! They found 54 lion-killed mule deer carcasses two years or older (since younger deer might not show signs of CWD infection , younger lion-killed deer were not used). Of these, 12 had CWD (22 percent), and there was some indication that bucks were more likely to be infected than does. So, you might think that lions seek out CWD-infected mule deer. However, to be able to say this, you would have to know t h e t...