As whitetail hunters have matured over the past 10 to 15 years, the bar has been raised on what constitutes a 'trophy buck.' One thing is clear. If you continually shoot 130-class 3 1/2-year-old bucks, you're unlikely to get a chance at a true 5 1/2-year-old bruiser. Photo by Bill Kinney.

Last month in Part 1 of this series, I talked to three top whitetail trophy hunters and reported on their opinions concerning the age at which whitetail bucks become fully mature. Adam Hays, Bobby Worthington and Tim Walmsley agreed across the board that, in their opinion, a buck is not fully mature until he reaches 5 1/2 years of age. 'Mature' in this sense means adult body and maximum or near maximum antler size.

While these three whitetail fanatics each have slightly different goals that they take to the woods with them in the fall each year, they've all helped reinforce some ideas that I've developed concerning mature bucks. This month, in an effort to get a little different insight from a professional biologist who has spent a lifetime studying white-tailed deer, I'll discuss this same issue with North American Whitetail's own Dr. James C. Kroll.

Certainly Dr. Kroll needs no introduction to the readers of this magazine or to the viewers of North American Whitetail Television. After our interview, I quickly realized that you can't possibly get a real idea of this man's knowledge and passion for whitetails until you actually talk to him. What's more, his ideas are not merely theories developed from limited deer sightings in a localized region. Dr. Kroll spends many days each year working and hunting in different whitetail ranges all across North America. In fact, when I spoke to him about this article, he had just returned from a whitetail hunt in Nueva Leon, Mexico.

INSIGHTS FROM DR. DEER
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.

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.

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