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At What Age Is A Buck Mature? Pt. 2


Dr. Kroll stated emphatically that in a properly managed herd, a whitetail buck is physiologically mature at 4 1/2 years of age. While there are always exceptions to the rule, generally speaking a 4 1/2-year-old buck will have 90 percent of the antler growth that he will ever have at any age. To some, it might seem that by letting a 4 1/2-year-old buck live another year, that 10 percent additional growth could turn a 150-inch buck into a 165-inch buck. Dr Kroll's studies have shown that this is not always the case, however.

In fact, some bucks often have smaller antlers at 5 1/2 years of age than at 4 1/2. This is due to the heavy toll that breeding takes on the bodies of 4 1/2-year-old bucks. Studies have shown that bucks often have their best racks at ages 6 1/2 and 7 1/2. After age 7 1/2, antler growth goes downhill, often very quickly.

Dr. Kroll's studies have proved time and time again that the majority of breeding is done by mature bucks 4 1/2 and 5 1/2 years old. This is true even in herds containing bucks older than 5 1/2. Keep in mind that we are talking about a well-balanced deer herd in terms of sex and age structure. Tests have shown that bucks 4 1/2 and 5 1/2 will have stronger and more viable sperm than bucks that are older or younger.

RELATED: At What Age Is a buck Mature, Pt. 1

In poorly managed herds, younger bucks are often forced to become physiologically mature ahead of their time. They actually engage in breeding even though their bodies are not yet fully developed. I found it very interesting that in Dr. Kroll's tests with captive whitetails, 2 1/2-year-old bucks that were placed in pens with does and allowed to be the primary breeders soon became physiologically mature. They even started looking and acting like older bucks because of their increased libido and testosterone levels.



Not surprisingly, the young bucks in these tests were significantly impacted in terms of antler growth in subsequent years. This is a perfect example of how the genetic makeup of a poorly managed herd is never truly displayed. In other words, if young bucks are doing the majority of the breeding, even those few that make it to older-age-classes will likely never express their true antler potential.

Another emphatic point that Dr. Kroll makes is that in properly managed herds, the mature breeding-age bucks actually breed very few does. Whitetails simply were not 'designed' to do a lot of breeding like some 'harem' animals. The scrotal circumference of a whitetail buck is actually small in relation to his body size when compared to other species such as elk or domesticated cattle.

Dr. Kroll says that the differences in a 3 1/2-year-old buck and a 4 1/2-year-old buck are startling. 'It's almost like talking about two different species,' he explains.

At 4 1/2 a buck's body is physically mature and he becomes 90 percent nocturnal, even in non-hunted herds. Another significant change occurs when bucks reach 6 1/2 or 7 1/2 years of age. These bucks still breed, but their libidos are significantly reduced and they are not as active as they were at 4 1/2 or 5 1/2. Dr. Kroll compares bucks in this age class to middle-aged men.


When it comes to his own hunting goals, Dr. Kroll practices what he preaches. Although his research has shown 4 1/2-year-old bucks to be physiologically mature, he always tries to shoot bucks that are 5 1/2 years old or older. In fact, last season he shot one buck that was 10 years old and another that was 7. Although Dr. Kroll does not seek to force his goals on other hunters, he does try to get others to see the benefits of a well-managed herd with a balanced age and sex structure. And even though one of the obvious benefits of a balanced herd is a higher number of trophy bucks, the driving force behind Dr. Kroll's passion to maintain a well-managed herd is that it is an ecologically sound approach.

Dr. Kroll probably has as much experience in whitetail management as any man alive. As reported in the October, November and December 2006 issues of North American Whitetail, he and Ben H. Koerth conducted an 11-year research project beginning in the mid-1990s in which over 7,000 buck fawns and yearlings were caught and tagged in South Texas. Many of those animals were recap tured when they were 4 1/2 years old, and their 4-year racks were compared to their first-year racks. The conclusion? A buck's first rack has absolutely no bearing on the size of the rack he will grow as a mature 4 1/2-year-old. The study clearly showed that numerous 'inferior' 1 1/2-year-old spikes grew beautiful 130- to 140-class racks when they reached 4 1/2.

As a result of this landmark study, Dr. Kroll became a strong proponent of not harvesting yearling bucks, even if they wear only spikes. His experience has taught him that the best way to limit buck harvest is to apply a no-take rule on deer having less than an outside spread minimum of around 14 inches. This allows practically every yearling buck in the herd to survive and it also protects a portion of the 2-year-old bucks in any given population.


My driving force for writing this article was to address the fact that many hunters use the term 'mature' when describing bucks they shoot. In reality, however, the bucks in question are not mature at all. I see this all the time in magazine articles, on TV shows and hunting videos, and in conversations that I have with other hunters. In fact, just last summer I ran into a man who hunts not far from a property that I hunt in Illinois.

This well-intentioned hunter was telling me about his previous season, in which he'd shot a 'real heavy 12-pointer that was so old he was going downhill.' I asked to see a photo. When he produced it, I didn't have the heart to tell this man that his 'over-the-hill' buck was in truth a 2 1/2-year-old youngster that I had passed on shooting several times. I also had numerous trail camera photos and some video footage of this young buck. This buck would have had a lot of potential if he'd been allowed to 'grow up.'

I've found that this misinformed hunter is not alone in his beliefs. I've seen countless 2 1/2-year-old bucks portrayed as 'mature' by hunters who are supposed to be 'experts.' It is even more common for many 3 1/2-year-old bucks to be mistakenly referred to as 'mature,' even though they clearly are not.

Most average hunters cannot properly age wild whitetail bucks on the hoof. Even with the considerable experience I've had in hunting mature bucks, I find it very difficult to age a buck after he reaches 4 1/2 years of age. The only way that I can do it with any degree of accuracy is if I have watched him grow up. However, I do believe that I can age bucks up to 3 1/2 years with about 95 percent accuracy.

With so much misinformation out there in print and on TV, it's little wonder that many hunters are confused about aging bucks on the hoof. However, Dr. Kroll believes that most hunters are capable of learning how to age bucks to the exact year with about 85 percent accuracy after taking a one-hour course that he gives on that subject.

Although it's great to see more hunters getting educated in this area, I have to wonder how much the 'average' deer hunter really cares about a buck's age and how many would even take the time to become educated at aging bucks if given the chance? It seems to me that antler score is still much more important to most hunters.

Even so, I hope that as the whitetail hunting community matures, we will see more and more hunters consider using age instead of score as a yardstick for harvesting 'mature' bucks. The bottom line for me is this: I think it's a shame for an experienced veteran hunter to harvest a 3 1/2-year-old buck, no matter what the rack scores.


As deer hunters, we all go through a maturing process. Some of us continue on that journey to the extreme limits while others stop and 'settle in' somewhere along the way. Practically all of us have shot young bucks when we first started deer hunting. There is nothing wrong with that. But how far you progress up the ladder is up to you and the effort you put forth.

As I strive to become better at hunting mature whitetails, I'm always looking for ways to take my game to a higher level. For the past few years, my goal has been to tag bucks that are 4 1/2 years old or older. Just like Dr. Kroll, I consider that age to be 'mature.' But what about top hunters like Tim Walmsley and Bobby Worthington who are convinced that we should wait for a buck to reach 5 1/2 before hunting him?

I think the answer is obvious. Bucks are individuals, just like people. Tim and Bobby have seen some real-life examples of bucks that put on significant antler growth after age 4 1/2. On the other hand, I've killed bucks each of the past two seasons that I'm certain were 4 1/2 years old because I watched these bucks grow up and I got them both on video as 3 1/2-year-olds. In my case, both of these bucks grew very little between 3 1/2 and 4 1/2 years of age. I had high hopes that each would be over 160 inches or even 170 inches as 4-year-olds, but both were barely over 150 inches at 4 1/2. And this was within a few inches of what they were at 3 1/2.


Just keep in mind that bucks are as individual as people; some reach their peak growth earlier than others. Most fit into the profile explained by Dr. Kroll and represent the 'average,' while others are outside the norm.

When I started working on this series, I had my own ideas about the age at which a buck becomes 'mature.' After interviewing three top whitetail hunters and a whitetail biologist who is in a class by himself, I have found that this project has been an honest learning experience for me. A lot of my ideas have been reinforced, and yet I'm left with as many questions as answers when it comes to my approach to hunting monster whitetails. For example, do I let a 4 1/2-year-old buck walk and take a chance that he will get bigger?

While I've been happy to shoot 4 1/2-year-old bucks for the past few seasons, I think I am now ready to take my goals to an even higher level. That is, I may still shoot a 4 1/2-year-old buck, but I will probably be a lot more selective in making that decision. I hunt a couple of properties where I feel confident that each season I can kill the biggest buck there no matter what his age. On those particular farms I might be more inclined to let a buck live past the age of 4 1/2.

On other properties where I know heavy hunting pressure is an issue, any chance I get at a 4 1/2-year-old buck may well be the only chance I get at filling a tag. In that situation, the buck is more likely to get shot. Each of us has to set his or her own goals. However, I can say without a doubt that the higher you set your goals, the better a whitetail hunter you will become. When you are sitting in your stand this fall, your 'buck of a lifetime' may waltz by wearing only his second or third rack. Take him now and you may never realize whitetail hunting's ultimate prize -- a mature buck wearing a world-class rack. Good luck!

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