By Dr. James C. Kroll
Years ago, Hungarian physician and scientist Dr. Hans Selye noticed a correlation between certain human diseases and a common set of symptoms. Many of his patients were suffering from what he called “simply not feeling good.” Their condition had three phases: (1) initial “alarm”; (2) resistance; and (3) exhaustion and death. Dr. Selye called these phenomena stress.
Suspecting an endocrinological origin, the doctor injected mice and rats with various extracts of glands and organs. In so doing, he identified what he considered a new hormone that allowed animals and humans to cope with physical and psychological trauma. Other researchers later identified cortisol, a hormone produced by the adrenal glands, as the agent involved.
This discovery produced excitement that a “wonder drug” had been found. Give a person suffering from poison ivy a hefty shot of cortisone, and the rash would go away. But the stressor didn’t actually go away — only its symptoms. The sudden release of cortisol was only meant to get the patient through a temporarily bad situation.
In a highly crowded, stressed animal population, at some point weird things begin to happen, including aberrant behaviors. That’s certainly true with whitetails. In fact, stress can be the most significant problem they face.
For over 20 years, we’ve been involved in health studies involving necropsies (animal autopsies) of deer at various levels of population density and habitat conditions. Most recently, we discovered at Turtle Lake Club in the northern Lower Peninsula of Michigan that bovine Tb infection could be mitigated by reducing stress on the herd. Working with club manager Wayne Sitton, we reduced herd density, improved sex ratios, boosted nutrition and manipulated the habitat to spread out the deer and eliminate yarding.
When we began work at Turtle Lake in 2004, the area the highest infection rates of Tb ever recorded in whitetails. It was plain to me that stress was the true culprit. Tb doesn’t spread easily among healthy populations, whether of humans or whitetails. Today we have virtually no Tb cases on that land.
Whitetail society consists of groups of closely related does (which I call “clans”) and small groups of highly vagrant males. In doe clans, there’s always an alpha doe that runs the show, meting out harsh punishment for transgressors! Yet this isn’t a source of stress — rather, it’s a source of tranquility and order. Disrupt that order and you see the system break down.
Buck groups also have a pecking order, and it makes life more pleasant for all members. Sadly, most modern herds are products of traditional deer management, with unnatural social structure that creates constant stress on members of the herd.
While inadequate nutrition can be caused naturally by climatic conditions, more often than not it’s a result of having too many deer on chronically poor habitat. All these factors combine to produce stress, and most hunters and mangers don’t even notice it.
EFFECTS OF STRESS
In does, stress can result in difficulty conceiving, high fetal mortality and/or high fawn mortality. And this can occur anywhere. Even in the Midwest, where does traditionally have high conception and birth rates, fawn mortality during the first two weeks after birth can be very high. Couple this with high winter fawn mortality and you have poor recruitment, which leads to lower buck availability for harvest.
Stress also affects antler development. A pecking order develops when bucks are fawns, continuing until they either die or move to other areas. Bucks lower in the social structure don’t grow antlers as large as those at the top. Interestingly, releasing small-racked captive bucks into the wild results in their developing larger antlers. That’s due to reduced social stress.
RECOGNIZING STRESS IN DEER
The herd is happy to “tell” you if it’s stressed. For example, how many fawns do you see, on average, with each doe? Are older does the only ones with fawns several months of age? Low fawn survival is a tipoff to herd stress.
Also, ever notice that some deer change coats from summer to winter and winter to summer later than others? Molting takes more protein than any other seasonal activity, so a slow-molting deer is stressed. If over 10 percent of does still have red coats in October, there’s stress in the herd.
Further, if fawns still have spots abnormally late, or you’re seeing fawns of various sizes/ages at the same time, stress is in evidence. A healthy herd’s fawns are born in a very short period.
An intense, brief rut, resulting from a tight sex ratio, actually reduces stress on bucks. A herd’s natural sex ratio should be around a buck per 1.5-2 does. A ratio more skewed than this will lead to chronic buck stress, as they must seek does longer and travel farther to breed all those available.
Also, while yearling bucks can and do breed, they aren’t meant to contribute much to the fawn crop. Normal buck age structure reduces stress and creates order in the herd.
Our Turtle Lake work clearly showed that herds without significant stress are less susceptible to disease. So it follows that if you commonly see strange maladies, diseases and parasites in deer, they’re under stress.
A harvested deer offers a treasure trove of information. If it’s covered in ticks and/or keds (flightless flies), it’s stressed. Heavy rump fat, kidney fat and mesenteric (organ) fat are clear indicators of good health. A lack of kidney fat is the best indicator of stress, especially in late season. Fat might completely cover the kidneys in October but be absent by January — especially in bucks.
If you’re aging the bucks shot on the property, do their antlers seem to be smaller than they should? What about the growth pattern of the antlers themselves? If they have large bases but quickly taper down to half the basal diameters as you move up each antler, that’s a sure sign of nutritional stress. Also, if there’s a lack of small beads (pearls) distributed in rows between the burrs and the brow tines, the buck has been under nutritional stress.
BASIC SOLUTIONS TO HERD STRESS
Should your observations show the herd is stressed, what can you do? Apply the tenets of sound management: (1) proper doe harvest to control growth; (2) native and supplemental nutrition management; (3) protection of young bucks for a more natural social structure; and (4) habitat management to improve winter and summer cover. These practices all can lead to healthier deer.