The Biology Behind QDM

By: Ted Wawrzyniak Biologist

By now, you have heard about the biological merits of QDM.  You have heard about how QDM creates a biologically sound and balanced herd.  So what exactly does that mean?  It is important that you know the answer to this question so you can help to spread the word about QDM.  To answer this question, let’s look at the two harvest strategies involved in QDM.  That is adequate doe harvest and restriction of the harvest of young bucks. 

Most importantly, QDM encourages adequate adult doe harvest.  Adult doe harvest accomplishes two things.  It is by far the most effective method of holding deer populations to a sustainable level and it balances the buck to doe ratio to a more natural level.  Adult does are the most productive segment of the deer herd.  They are the most likely to successfully raise one, two, and even three young the next year.  So by taking an adult doe, you take out 2-4 deer from next year’s deer population.  The harvest of a buck or a fawn only eliminates one deer.  On the surface, this may alarm some people.  You may anticipate a large decline in the population.  Some have asked, “What happens if we have a bad winter?”  This is exactly why we need to decrease the deer population.  Before I explain what I mean, let me give you a couple definitions.  The carrying capacity is the maximum level that a particular habitat can maintain.  This capacity goes up and down with certain conditions.  With recent mild winters, this capacity has increased steadily.  In some of the more agricultural regions, this capacity has increased even more than other areas.  I doubt that we are at that level because we would have to have virtually no hunting season to maintain this, however, we are likely very near that level.  This is why you see the liberal doe harvest limits.  Another level which is extremely important is the sustained yield.  This is a level in which the maximum number of fawns are born and survive.  This is a level in which deer are in the best condition, in which they have plenty of food, cover, and water.  Their weights going into winter are the highest and they show an increased resistance to stresses.  Now, I can go back to why we need to lower our deer population.  Currently, with the state of the deer herd, a severe stress such as disease or a bad winter could decimate the population.  With the population at this lower sustained yield, the deer will likely be more than adequately prepared to deal with any stress that it could face.  Deer populations will remain much more stable and predictable.  This makes deer populations much easier to manage.  When populations are near carrying capacity stresses such as bad winters can bring the population to well below sustained yield levels, possibly requiring the DNR to severely restrict harvest or even cancel the hunting season all together for a year or more.  The DNR tries to manage deer numbers closer to the levels of this sustained yield.  I have not been able to have a discussion with a DNR Biologist regarding what level they try to maintain, but it is generally 50-60 percent of the carrying capacity.  The DNR regularly evaluates what levels they would like to maintain in each area of the state based on a particular sustained yield and sets harvest regulations based on that level.  There is much more population dynamics that go into population levels being held near carrying capacity, but that goes beyond the scope of what I want to accomplish with this article.  You can increase the sustained yield level in your area by planting food plots and managing your habitat to provide food and cover.  These areas are covered in other parts of this and other newsletters.

A natural buck to doe ratio is about one buck for every doe (1:2).  It was proposed by Guynn (1991) that deer herds should be managed so that the natural structure of populations is maintained.  This goal ensures that the behavioral and biological mechanisms that shape deer populations are allowed to function.  The density, sex ratio, and age structure should mimic a population regulated by natural predators and hunting by the Native Americans.  Elder (1965) reported age composition of prehistoric Native American deer harvest based on mandibles from three sites in Missouri.  Age compositions from the sites are remarkably similar and suggest that the Native Americans killed few fawns (8 percent or less), many deer survived to older ages (20 to 26 percent was 6 ½ years or older), and longevity of deer was great (some deer were 10 ½ years or older).  Obviously, we are currently nowhere near this level with our harvest.

The other harvest management strategy that QDM promotes is a restriction in the harvest of young bucks (all of the yearlings and most or all of the 2 ½ year olds).  This will create a buck age structure that consists of many more mature bucks in the population.  This improved age structure, along with a balanced buck to doe ratio, is what we are talking about when you hear about a “natural or balanced” herd or population.  It is what QDM advocates consider a “biologically sound” herd. 

So what does this all lead to?  What does this create other than simply “larger racks”?  Of course, you see bigger and healthier deer all around (including does) that are able to maintain a steady population level through all the stresses that they may encounter (winter, drought, disease, etc.).  What you don’t see is that only the older, most dominant and genetically superior (and healthiest) bucks are doing the breeding.  This allows for natural selection to run its course.  You not only have genetically superior bucks, but you have genetically superior does as well.  In the presence of mature bucks, the testosterone levels of yearling bucks is suppressed, resulting in only the superior, mature bucks that win the right to breed to do the breeding.  Does are generally bred over the span of 30 days rather than 90.  Now you want to talk about a quality hunt.  The sight of a mature buck charging to your grunt call, doe scents, and rattling antlers is just about the most rewarding experience anyone can achieve (even if you don’t shoot anything).  Very few hunters in Minnesota even know what this feeling feels like, but when they do, they will never want to go back.  These 30 days will be the most intense period of time you could imagine.  This is in my opinion, a hunt of greater quality than anything that is possible right now.  And I’m not even talking about shooting anything yet!  At this point, it really doesn’t matter.  Remember, the sport is called hunting and not shooting.  I have had years where I did not shoot a deer and still had a great time while I was “hunting”.  Yes, it would be nice to have a nice buck on my wall, but the experience is what most QDM advocates are after.  In fact, I would have even a greater experience shooting does if I know that I may get to see a buck every time I go out and blow on my grunt call.  Maybe my wife would even quit yelling at me every time I came home smelling like doe pee, knowing that I actually have a chance of that stuff working.

The biggest complaint you hear from some people is that QDM is all about “large racks”.  This is a statement made only by the uneducated, because as you can see, QDM is a package deal.  No, there really is no detrimental effect of having a buck to doe ratio of 1:7 (as an example).  You can’t give a simple explanation of why it is wrong to have a messed up buck age structure in which 90 percent of all bucks are yearlings or less.  It is all tied in to a larger picture of which doe harvest is the cornerstone.  If you don’t believe that, than QDM is not for you.  If all you are trying to get out of QDM is “larger racks”, please move to Texas and practice what you truly mean to practice – trophy management.  QDM in Minnesota is going to be what it truly was meant to be.  That is something that focuses on the big picture.  Looking at the population as a whole and using sound biological principles to attain a hunting experience that is of the highest quality possible. Yes, larger racks are a product of a more natural population.  That is what gets all the attention because they are promoted on TV shows, magazines, and in hunting clubs.  Unfortunately, you don’t see too many pictures in magazines of the mature doe that someone shot during muzzleloader season.  It is human nature to want to get something that is bigger than everyone else’s.  I will admit that I dream of shooting “The Big One”.  But how can you not get excited about that.  We as deer hunters do not have to make any excuses about our passion for deer hunting and the quest for a trophy.  But anyone practicing QDM knows the importance of doe harvest and how it all ties into the big picture.  In addition to that, I haven’t even mentioned that QDM advocates often use does to fill their freezers with delicious meat. 

Make sure you make plenty of copies of this article, because next time you get a question like: “What is a balanced herd structure?” or “Why do you want a balanced buck to doe ratio?” or “Isn’t QDM only about bigger racks?”, simply tell them that QDM is a package deal.  It can’t really be explained in one part.  Give them this article.  I think it will help them to get a feeling of why we practice QDM in Minnesota.  They can email me at tedw@mnsporstmen.com if they have any more questions.  From time to time, I may adjust or add to this article, so please check our website (www.mnqdm.com) for the latest version.  I hope this article will influence they way you approach your hunting season this year.  If it does, please email me with how it changed your experience.  I always enjoy hearing about those sort of things.