Reprinted from an Oct 29, 2006 column in Morgantown Dominion Post, plus material in "Whitetail Advantage" found elsewhere in this website.
It is almost the time of the rut, when bucks mate does. For bowhunters, this is an exciting time, because we get to see all kinds of behavior and listen to vocalizations not heard at other times of the year. Things are happening. Bucks fight, bucks chase does, they call, and they mate does.
Growing up I learned that it was the mature, biggest, baddest bucks that did the breeding. They were dominant and the smaller bucks understood that and stayed out of the way. Most hunters believed this was reality, but is that really what happens?.
A few years ago, DNA studies were conducted on penned does and bucks to determine what bucks did the breeding. Bucks 3 ½-years-old and older were put in pens with does, and sure enough, in most cases, the 5 1/2-year-old bucks did a high percentage of the breeding. However, in some instances the 3 ½-year-old bucks were dominant and did most of the breeding, even over 5 ½-year olds. That’s interesting. Why would those younger bucks mate does when older bucks were present? One researcher speculated that the weight of the bucks was more important than age when it came to dominance and breeding. Sounds logical and that appears to be the case.
In another experiment yearling bucks were put in pens with 2 ½-year-old bucks, and in almost every instance, the 2 ½-year-old bucks did the breeding.
That is what happens in pens, but what goes on in the wild, especially in our part of West Virginia? There are several factors that need to be discussed as we attempt to determine who mates does. First, the number of does in an area will impact who does the breeding. In much of West Virginia the sex ratio is probably around 6 adult does for every adult buck. Does this mean that mature, older bucks mate all these does? Not really. They can’t.
Consider that the peak of breeding takes place between November 10-15 in our region (and most of the northern whitetail habitat in the United States). Not all does come into estrus during that period, but most do. So, if only older bucks bred does, they would have to get it all done (or most of it) during this one week period. Consider also that when a buck finds a hot doe, he stays with her for around two days before breeding takes place. Knowing this it is obvious that mature bucks can’t mate all the does.
Add to this the simple fact that there are not many mature bucks in our region. We harvest around 80 percent of all harvestable bucks every year, and that means that at the most, only 20 percent of our bucks live to 2 ½ years of age. Even fewer live to age 3 ½. So, with the sex ratio mentioned, and a relatively small window of receptivity, it is obvious that older bucks cannot mate all does in our region, and it turns out that they don’t in other places either.
Even when there are mature bucks living in an area, yearling bucks and 2 ½-year-old bucks will do some breeding. They find a hot doe and mate her, and then an older buck comes along and mates her too. We know this happens because DNA studies show that some twin fawns have different fathers, and in every case, one father was a yearling or 2 ½-year-old buck and one father was an older buck. You also have the situation where a mature buck is with an estrus doe. Other estrus does in that area will then be mated with young bucks, simply because the mature buck is already busy.
In a normal, healthy herd, the doe to buck ratio should be 1 to 1 or 2 to 1. Even 3 to 1 isn’t bad, but we don’t have that in most whitetail range because hunters don’t, can’t, or won’t, harvest enough does. Any farmer can tell you that his farm fields can support only so many healthy animals. Put more in there and the habitat suffers and the animals lose weight. Same for deer.
A habitat can only support so many quality deer. Let’s assume that the adult sex ratio is 4 adult does to every adult buck. Lets further assume that the habitat in an area can only support 100 deer. In this scenario, 80 will be does and 20 will be bucks. But if you harvested more does and got the sex ratio down to 2 to 1, you could have around 35 bucks. And if you got the sex ratio to 1 to 1, then you would have 50 does. Obviously if you had that kind of sex ratio in an area, older bucks would mate more of the does, simply because there are more older bucks and fewer does.
There is also some new research that mystifies most hunters. Several studies show that a few older bucks --- the biggest, baddest bucks in the area --- don’t sire any fawns. They just do not participate in the rut. Hmmm. What the heck is that all about? For deer hunters it is just another part of the puzzle that we will probably never understand. But it is so much fun being out there and trying to piece that puzzle together.
