When it comes to body size, those Maine, Saskatchewan and Alberta whitetails seem to win hands down. We’ve read for years about the 300-pound bucks from Maine, and we’ve seen the big-bodied bucks from Saskatchewan and Alberta on television hunting shows. The reverse is true for body weights of deer from the South. The subspecies in Mexico, Texas and Florida, on average, are quite small compared to their Northern relatives.
A lot has been made about something called Bergmann’s Rule, which states that the body size of a species increases with latitude. The theory is that bigger bodies can conserve more body heat in regions where it is cold because there is a relationship between body size and body surface area; the bigger the body, the relative less surface area there is. This means that bigger animals radiate less body heat per unit of body mass, thus conserving energy. Conversely, in hot and dry climates, the higher surface-area-to-volume ratio means more heat loss through the skin, and this helps cool the body. That’s Bergmann’s Rule. Bigger body size for the species in the North, smaller body size for the same species in the South. That’s the theory, but does it hold up for whitetails?
The answer is “yes,” Bergmann’s Rule seems to hold for whitetails, because the farther north you go, the bigger the body of the animals. That being said, why are there variations? All those Northern bucks aren’t big, and all those Southern bucks aren’t small. Perhaps the reason we can always find some bigger-bodied bucks throughout whitetail range is because body size is affected by two things — how much food is available, and how many other deer are out there competing for that food.
Take Texas, for example. No question that, in general, Texas deer are smaller (in body size) than deer from the North. There are regions in Texas where there are very high numbers of deer, relatively little hunting pressure, and small body sizes. If harvest increases in those areas, deer body weights will most likely increase. The bottom line is that in most places, the more food produced for deer to eat, the bigger the body size of those deer. Given enough food, you can still get heavy deer even if population density is high. That isn’t generally the situation, but it can happen.
We know that Bergmann’s Rule holds pretty well for deer, and we understand that there are variables that also affect body weight, but what about antler sizes? If body size of bucks is bigger in northern regions, are antler sizes also bigger? Conversely, if the bodies of more southerly bucks are smaller (which they are), are the antlers smaller there too?
I took a quick look at the Boone and Crockett 1999 record book for typical whitetails and found that in the top 20 bucks, there were three from Saskatchewan, Minnesota and Michigan (each), two from Alberta, Missouri, Illinois and Iowa, and one each from Kansas, Wisconsin and New York. I looked at typical whitetail bucks harvested by bows in the Pope and Young Club 2011 record book and found six from Iowa, three from Illinois, two each from Ohio, Minnesota and Kansas, and one each from Saskatchewan, Alberta, Colorado, Michigan and Manitoba. No question, the farm country of the Midwest and more northerly provinces such as Saskatchewan and Alberta has some great bucks. My quick look at the top 20 bucks was a small sample, so has anyone collected hard data that looked at antler sizes in different geographical areas?
Turns out that there have been two studies that looked at this phenomenon. Sadly, only one has some data from Canada, and even that one has no data from the big-buck provinces of Alberta and Saskatchewan. Even so, there is good data from both studies, so here is a summary of both.
The first study was done by Joel Helmer, a professor in the geography department at Oklahoma State University. He mapped more than 5,000 Boone and Crockett record-book entries into county maps for the entire United States. To make it more interesting, he divided the entries into those bucks taken from 1830-1979, and those bucks taken from 1980-2001.
He had 1,489 entries from 1830 to 1979, and the top states were Minnesota, Wisconsin and Texas. One might have expected Iowa, Illinois or other Midwest farm states to be in the top three, but they were notably absent. The probable reason was because deer were relatively rare there in the early years, and deer numbers in the Midwest just started to get going in the early 1980s. The forested areas of Minnesota and Wisconsin held better deer numbers throughout that period when compared to the farmed areas of the Midwest. Texas is in the top three because south Texas always had some good bucks on the private, well-managed ranches there. They obviously still do.
In the early 1980s, deer range expanded and numbers started to grow. Within 10 years, many deer were found in farm country. That population explosion of whitetails was not just in the Midwest. Deer numbers jumped from New Jersey to Montana and most parts in between. With the expansion of range and the huge increase in deer density, hunters had the luxury of being able to focus on bigger bucks. Thus, more bucks were entered in the record book, and for the period of 1980 to 2001 we started to see more and more bucks from Midwestern farm states being put into the record books. Overall the top states were Illinois, Iowa, Wisconsin, Minnesota, Missouri, Kentucky, Kansas, Ohio, Texas and Indiana. Minnesota was still in the mix, but now the bigger bucks were coming from the farmland in the southern part of the state.
There is no question, if you want to shoot big bucks, the Midwest is the place to do it. Of course, south Texas was and still is a great place to go, simply because the private ranches there provide great feed, restrict shooting younger bucks, and spend lots of money to manage their valuable resource. Body weights might not be as high as far-northern bucks, but big antlers will always be found on south Texas ranches, regardless of Bergmann’s Rule.
The second study was more recent and was done by Drs. Bronson Strickland and Steve Demarais, wildlife professors and researchers at Mississippi State University. I know both of these men, and better deer researchers would be hard to find. Their study appeared in Quality Whitetails magazine and centered on antler beam sizes for yearling bucks. They didn’t use Boone and Crockett scores simply because few states take such measurements at deer check stations. It just takes too much time. But some states and a few provinces (but not Alberta or Saskatchewan, and that’s a shame because it would be nice to have that data here) do collect data on antler beam diameters.
So Strickland and Demarais asked state and province wildlife agencies for antler beam diameter data. They received 74 sets of data, and although they got little data from the Canadian provinces, they found that Bergmann’s Rule just did not explain antler beam diameter for yearling bucks (see Figure 1). Antler beam sizes from areas in New Brunswick and Maine were the same as antler beams in parts of South Carolina and Louisiana.
Overall, the data sets with the largest antler beam sizes came from the farm country in the Midwest. If latitude doesn’t explain variation in antler beam diameter, then what does? What are the variables that explain why you get bigger antlers in some places, and smaller antlers in others?
There are several factors, not the least of which is the soil. Remember that calcium and phosphorus make up one-third of the weight of antlers. Those minerals are very important to antlers, and the growth of antlers and what deer eat is very important relative to getting enough calcium and phosphorus. Those minerals, and the plants containing them, are best found in moist well-drained soils found along major rivers.
The Midwest farm country is great for raising crops, and one reason is good soil. In fact, farming along rivers is very productive, because rivers flood — and this puts more good soil on the lands bordering rivers. Good for crops and good for forbs that deer love to eat.
Even better for big antlers are Midwestern farms that also have some forest cover along the river bottoms. Those forests provide some cover for deer, and they also provide acorns. Combine this with the nutritious farm crops growing along rivers and you get big antlers. No question, the Mississippi, Ohio and Missouri rivers, as well as their tributaries, are major reasons we find bigger antlers in the Midwest.
There are lots of other variables that impact antler sizes. Areas with high deer densities tend to have smaller-antlered bucks. States that allow multiple buck kills (and thus more yearlings harvested) tend to have smaller-antlered bucks. There are exceptions, but it’s a good rule of thumb. Consider that Indiana and Kentucky both had major jumps in antler size in the past 20 years when they lowered the number of bucks a hunter could harvest in one year.
Where the rifle season takes place relative to peak rut will also impact the number of bucks harvested. If the gun season falls before or after peak rut, then bucks are less vulnerable and more can reach mature size. The fact that many south Texas ranches do not allow bucks less than 4 or 5 years of age to be harvested is one of the reasons that area produces some really good bucks year after year. Managing bucks so that you get older age classes is one reason that, relative to antler size, Bergmann’s Rule falls flat in Texas. Management trumps latitude.
Throughout deer range, soils and good feed explains antler size more than Bergmann’s Rule. Hunters, leasers, land owners and land managers can do a lot to get healthier and heavier bucks and does on their properties, no matter where they are. Managing habitat and the deer is why we find big bucks and healthier deer scattered all over whitetail range.