March 17, 2011
By Dr. James C. Kroll
I am closing in on my fourth decade of whitetail research and management. A great deal has changed in those years, but nothing more striking than the concept of doe harvest. As a teenage hunter, there was one thing you just would not do -- shoot a doe!
When I came to eastern Texas in 1973, if someone saw a deer track it would be the topic of conversation for at least a month. By the end of that decade, leasing and formation of hunting clubs was leading to more deer, and by 1980, I was becoming worried about the future.
I gave a talk at a Noon Lion's Club meeting near Nacogdoches, Texas, around that time, and I turned to the concept of doe harvest with plans to make my point. An old woman near the back of the room picked up a dinner roll and threw it straight at me. Her aim was deadly as it bounced off my forehead. "Who is your mother?" she yelled. The audience erupted in laughter and applause.
Today, although most hunters fully understand the need to control deer populations through doe harvest, there still are pockets of folks who do not support the practice. Still others are confused about how many and which does to shoot. I'd like to clear up some of the confusion and misconceptions, hopefully simplifying things a bit for you.
I hear a lot of ideas kicked around about what is the perfect sex ratio for whitetails. Professional biologists have not made things any more clear due to the way they refer to herd demographics (sex and age structure of a population). For some time I have been critical of the way some states manage their herds, primarily in relation to sex ratios. Many states claim a balanced harvest or even one weighted in favor of "antlerless" harvest. That is the problem. The term antlerless does not equate to "doe." Buck fawns often are counted into these estimates, but that's not what I'm talking about when it comes to sex ratios.
The sex ratio I use is calculated by dividing the number of does that are 18 months or older ("long-yearlings") by the number of bucks of the same age. In order to be counted in the sex ratio, a buck has to have some bone on its head. The reason I exclude buck and doe fawns in these estimates is that mortality is high in this age class, and you cannot count them in the breeding population until at least one year of age. Given this, every study I have done suggests the "natural" sex ratio for whitetails is between 1.5 and 2 does per antlered buck. I feel strongly that was the sex ratio encountered by the first humans reaching North America. The reason is, just like humans, the males lead a more stressful life and have higher early mortality rates.
The mythical 1:1 ratio probably seldom happens. Furthermore, as you approach a more equal sex ratio, antler breakage and mortality increases dramatically. So, in most instances, if I can achieve a 1:3 buck to doe ratio, I feel pretty good about the management program. That ratio represents a compromise between lager numbers of mature bucks and hunter success. A good age structure for a managed deer herd resembles a pyramid, with the oldest individuals at the apex. Buck mortality is additive, and the abundance of bucks surviving their first three years -- even without hunting pressure -- declines.
WHICH DOE TO HARVEST?
For years I have heard old time biologists, especially in the Great Lakes states, assert you need older does to successfully reproduce. The problem lies in that these professionals have spent their entire careers studying deer living in stagnant herds! Yes, if we have old doe age structure and skewed sex ratios, it does indeed take a doe three or more years to successfully reproduce. Yet, if that same herd is brought into line with the productive capacity of the habitat, we suddenly see young (two- and three-year-old) and even yearling does reproduce just as successfully.
In my deer management seminars, I often say tongue-in-cheek, "Men, in deer management, it is a perfect world -- old bucks and young does!" What we are after demographically is just that -- older bucks and younger does. The reason is nature meant for bucks to have to fight their way up the ladder to maturity. That guarantees stronger, more adaptable individuals. When you have a situation in which 70 percent or more of the antlered bucks taken each season are yearlings, it is mathematically impossible to have older bucks! In such a case, untested and immature individuals father most of the fawns. When you add in a stagnant herd, in which only the old does successfully recruit a fawn, genetic stagnation is the end product. My observations and experience clearly point to the fact that such conditions result in smaller antlers and lower fitness levels.
When you have younger does successfully recruiting offspring, genetic diversity goes up and antler size increases. But, is this natural? In pre-human times, whitetails lived in forests which eventually grew older and closed up their canopy. The resulting low light conditions significantly reduced forage production, in turn reducing the number of deer the area would support. Age structure increased as recruitment declined. Then suddenly a catastrophic event such as a tornado, hurricane or wild fire opened up the forest, releasing nutrients for lush forage growth. For the first 5-7 years, reproduction increased, producing a herd with young age structure. The survivors (notably bucks) from poorer conditions ultimately produced the most offspring. It has been my experience -- and I cannot tell you why -- that a doe's first three sets of offspring will include her largest antlered sons.
So, to answer the above question, you should focus harvest strategy in such a way to decrease average doe age. This can be done in two ways. The first is to target older does, requiring you to learn to age live deer. This is not all that difficult. An older doe is not always the largest in the group, especially under good management. Rather, she is the one with the "mulie" appearance and dominating demeanor.
The best way, in my opinion, to reduce doe age structure is to harvest enough does from your land to accomplish this mathematically. When I begin a management program on a new property, my first direction is just harvest "some" does. A general rule-of-thumb is to harvest one doe per 100 acres minimum.
The metric I use goes as follows: If the percentage of does harvested that are 2 1/2 years or younger is greater than 50 percent and less than 60 percent, you are harvesting the right number of does. If one of the other situations occurs (less than 50 percent or more than 60 percent), you either are not harvesting enough does or you're taking too many does. Lastly, if you are taking does in the 5 1/2-year-old or higher age class, I promise you are under-harvesting your does! I strive to truncate my doe age structure at 4 1/2 years.
Finally, I often am asked about "culling" does. Obviously, there is nothing about the outward appearance of a doe giving any indication of her genetic quality. Yet, it is indeed possible to manipulate genetics through doe harvest. If you are managing for a young doe herd and protecting older bucks, in effect you are genetically selecting your deer. After all, if there are some older bucks that make it through the season, their experience will permit them to breed more of the young does.
It all boils down to managing your herd to maximize productivity. To accomplish this goal, you must keep your habitat highly productive, your herd beneath saturation level, and demographics that promotes genetic diversity.