Age, nutrition and genetics are the key factors that determine how big a buck’s head gear will grow.
As deer hunters, our hunger for bigger and bigger antlers seems insatiable. Barrels of ink have been emptied as writers write about and researchers research ways to grow bigger antlers. There is much we stand to learn, but we have already amassed an impressive amount of knowledge about the things that contribute to large antler size. At the most basic level, we know there are three building blocks in the trophy antler equation: age, nutrition and genetics.
Age is the most obvious and easy to understand portion of the equation. We learned long ago that antler size increases with age through the years of peak antler growth (generally 5 to 7 years). If we don’t let bucks grown old, we are not going to see big antlers. Almost as important as age is nutrition, which supplies the building blocks of antler material. Realizing that there was a relationship between antler size and diet quality, William Twiti in 1327 remarked, “The head grows according to pasture, good or otherwise.” Nearly 700 years ago they knew that deer needed good nutrition to grow good antlers.
That brings us to the third factor in our equation. Each buck has a different genetic potential for antler growth. Captive bucks of the same age, fed the same diet, show antler shapes and sizes that are very different from one another. Some bucks will be superior to others at the same age and some will never have large antlers, just as some humans never reach 6 feet tall regardless of diet or age. Every population has some individuals that have genetic potential for antler size that is far above or below average for that population. It is tempting to blame small antlers in an area on “poor genetics” because it’s such an easy scape- goat for explaining the lack of big bucks. There is much talk in some circles about how hunters and deer managers can affect the gene pool.
MEET THE GENE POOL
When it comes to deer populations, our interest in genetics usually revolves around what effect humans might have on the gene pool — either positive or negative. To alter the gene pool we would have to cause a shift in the percentage of animals that carry genes for a certain trait.
Of course, this is most often related to big racks. We have the potential to alter the gene pool anytime we influence which deer remain to do the breeding for the next generation. This includes selectively harvesting trophy bucks, culling undesirable bucks, establishing harvest restrictions based on antler size and translocating deer. While it might seem obvious that we could change the gene pool, a closer look reveals it is much more complex.
To impact the genetics of a population, antler traits must first be strongly inherited. If the biggest-antlered bucks don’t consistently produce sons with above average antlers, then there is nothing we can do to change the proportion of “good” antler genes in the population.
Early work with pedigreed captive herds illustrated that individual deer have a wide range of different genetic potentials for antler size and shape. It has been shown that a buck’s antler size and shape are related to those of his father or grandfather and so we know antler characteristics are inherited to some degree. This means we at least have the potential to influence antler size by altering which bucks are doing the breeding.
The second element that is necessary to affect the gene pool is selection. Selection refers to anything that removes future breeders from the population based on some characteristic rather than at random. Anytime we shoot a trophy buck for the wall, shoot a spike or cull buck, or let a legal animal walk away from our stand, we are engaged in the selection of future generations of breeders. The fact that we are selecting is not as important as how intensive the selection is. Obviously, shooting a big buck in your area doesn’t mean there will be any change in the future ability of that population to grow big deer.
THE DIFFICULTY OF ALTERING ANTLER GENES
Captive studies on antler inheritance and selection were important first steps to learning if we even have the potential to influence the gene pool of wild populations. Years ago, Texas whitetail enthusiast Stew- art Stedman introduced an important concept he called the “Corral to County Continuum.” Stedman said what you can accomplish in captivity (a corral) is difficult to reproduce at the county level. In the case of genetics, everything hinges on how intensively you are selecting for or against superior antler traits.
We have to think of selection intensity in relation to all of the other things that are removing deer from the population and determining who will be next year’s breeders. In most populations, factors such as malnutrition, coyotes and disease take more than half of each year’s fawn crop. If all these removals by other mortality factors are at random in relation to antler size, that is going to dramatically dilute any effect hunter harvest has on the gene pool. There are, in fact, many obstacles that stand in our way of positively or negatively changing the gene pool in terms of antler quality. A few that have been identified are:
• Trophy hunters usually shoot the oldest deer they see, not the most genetically superior in that age class.
• As many as 30 percent of the fawns can be fathered by yearlings and 2 1⁄2-year-old bucks, not by the most genetically superior trophy bucks in the area.
• Does contribute half of the genetics to the antler quality of her male offspring and all of those does can’t be selected for antler quality genes (and does make up 80 percent of the gene pool when you have a 1:4 buck:doe ratio).
• The same deer might be a cull buck in a poor nutrition year and one to “let walk” during a good year — and none of those decisions would be based on genetics.
• Late-born fawns have a higher proportion of spike antlers when 1 1⁄2- year-olds because they are behind in body development regardless of genetics.
• The nutrition of the doe while she is pregnant can have lifelong effects on the antler quality of her offspring.
• Genes related to antler quality can be linked to other genes that have a stronger connection to whether they live or die.
In recent years, there has been an increasing number of academics criticizing trophy hunting as being bad for the gene pool. In other words, they charge that the removal of big bucks is leaving only inferior bucks to breed and thereby ruining the genetics of the herd. This argument is based on speculation that hunters are selecting genetically superior animals intensively enough to overcome all of the obstacles listed above.
But even trying to define what a trophy is, can be problematic. One trophy hunter might be satisfied with a buck that another hunter has already passed up in her search for what she feels is a trophy. If one hunter’s trophy is another’s reject, how can we meaningfully discuss the genetic effect of removing “trophy” deer, especially when trophy hunters are mostly just taking the oldest deer, not the most genetically superior.
Any deer population is made up of a mixture of small, medium and large antlered deer of varying ages. Many analyses have shown that there is too much overlap between whitetail antler size and age class for a hunter to tell an exceptional 3 1⁄2-year-old from a poor 6 1⁄2-year-old. In reality, trophy hunters usually just take the largest bucks they encounter within rifle range, during the season, during daylight hours and while they are in the field (if they don’t miss!).
CULLING GENETICALLY INFERIOR BUCKS
Some hunting clubs and intensively managed properties are attempting to improve the gene pool by setting harvest rules with the intent of removing genetically inferior animals from the population. This is obviously complicated by the inability to know the age of the deer you are selecting as a cull. The most familiar form of culling is the practice of removing spikes from the population. The preponderance of evidence from both captive and free-ranging herds indicates spikes do always remain a little behind their forked yearling cousins in the antler department. With this knowledge, it seems like a reasonable way to remove “inferior” animals from the gene pool, but there’s a lot of non-genetic factors that contribute to a yearling buck having spikes rather than forked antlers. Nutrition is the most obvious, but all of the obstacles that keep us from harming the gene pool also keep us from trying to improve it.
At least three well-designed studies have attempted to improve the genetic potential of a deer population through culling of bucks with below average antlers. In one study, they captured more than 5,000 bucks during a 10-year period and culled more than 1,000 of them because their antlers measured below average for their age. This is much more intensive than any recreational harvest scenario and more than all but the most intensely managed herds. In all cases, researchers found no evidence of a genetic response to their selective removal. It is becoming clear that culling does not work in free-rang- ing deer populations at Stedman’s “county” end of the spectrum.
ANTLER-BASED HARVEST RESTRICTIONS
One increasingly common harvest structure is harvest restrictions based on antler size, where the deer must have a certain number of points or minimum inside spread. This creates a situation where a disproportionate number of older deer are removed compared to hunters taking deer at random. Antler-based restrictions are usually implemented when managers have a high number of hunters and they want to limit harvest to allow bucks to reach an older age.
Although some hunters see all of these restrictions as a trophy management scheme, the purpose was really just to allow the age structure to mature somewhat. In many cases, depending on the criteria used, these restrictions mostly just allow yearlings to survive another year. In heavily hunted areas, most bucks are removed as soon as they reach the minimum criteria.
Some have expressed concern these harvest restrictions could high-grade the bucks and remove the best genes. In the yearling age class, a large proportion will be spikes and some will have branched antlers. If you establish antler restrictions so that bucks must have forked antlers to be legal, the best yearlings of each fawn crop are removed. This is a much more intensive selection scenario, but is it enough to affect the gene pool?
All of the obstacles listed above make it extremely difficult for hunters to exert selection intensive enough to change the genetic make-up at the population level. If the intensive culling research was not able to make a detectable genetic change it is doubtful antler restrictions on less intensive recreational harvest could degrade the gene pool in any meaningful way.
A REALISTIC LOOK AT THE ANTLER GENE
As of yet, no one has located “the antler gene,” and it is doubtful anyone will because the relationship between genes and physical characteristics is rarely that simple. There are probably many genes that act together to determine the shape, size and mass of a white-tailed buck’s antlers. The expression of these genes is related to a buck’s ability to efficiently process his nutrient intake and survive to a ripe old age.
The high genetic diversity in deer, along with all the other mortalities that are unrelated to antler size, work to “reshuffle” the genetic card deck, preventing a noticeable change in the overall antler quality of a deer herd. Hunter harvest is not the only thing removing deer from the population, nor is potential antler size the main criteria for removal. If you want to increase the proportion of “good” genes in the herd during a person’s lifetime, your selective removal has to be persistent and the overwhelm- ing influence in who breeds next year.
When a deer population lacks a reputation for having big bucks, the blame often falls to poor genetics. It is difficult to prove or disprove such theories, but genetics is unlikely the reason a population isn’t producing as many Boone and Crockett bucks as we would like. A relatively young age structure, too many deer, and generally low nutritional level of the habitat are the most likely culprits. Age structure is simply an issue of buck harvest intensity and very easy to adjust, but improving nutrition requires a deer density reduction or improvement in habitat quality. We would be doing deer a favor if we spent more time keeping the deer populations at an appropriate level for the habitat and didn’t spend so much time worrying about the gene pool.
— Jim Heffelfinger is a certified wildlife biologist who has worked as a biologist for the federal govern- ment, state wildlife agencies, univer- sities and in the private sector in Texas, New Mexico and Arizona. Jim has authored or co-authored more than 200 magazine articles, dozens of scientific papers, and 19 book chapters in regional, national and international publications, including his book, “Deer of the Southwest.” He is an adjunct professor at the University of Arizona, Professional Member of the Boone and Crockett Club, and currently works as Wildlife Science Coordinator for the Arizona Game and Fish Department.