Harvesting Cull Bucks – Pitfall or Panacea?

Hunters use many terms to describe them including cull bucks, scrub bucks and junk bucks, but their message is always the same – you should remove them from your deer herd because of their inferior genetics. On the surface, their logic appears sound – if bucks with poor quality antlers are allowed to breed, the local “gene pool” will be negatively impacted and the buck’s undesirable antler traits will be perpetuated. But, is this logic based in Whitetail Science?

Before discussing the research, let’s review basic genetics. First, when is the genetic code for antler development established? That’s right, at the time of conception. As simple as that sounds, I’m constantly surprised by hunters who, after harvesting a buck with malformed antlers clearly resulting from a body or antler injury, take great pride in removing a buck with “bad genetics.” Bottom line, anything that happens after birth that causes a buck to have malformed antlers is not genetically based. In fact, the vast majority of bucks with “messed up racks” are not the result of bad genetics, but rather an injury to the buck’s body, skull or growing antlers.

Second, which parent – the doe or the buck – most influences the antler potential of their male offspring? Based on research by Dr. Harry Jacobson and others, the doe has a greater influence than the buck, though only marginally. This begs the question of how hunters could ever identify a genetically-inferior doe?

Third, a recent study by Dr. Randy DeYoung has shed new light on genetics in wild deer populations. Armed with modern DNA techniques, Dr. DeYoung examined buck breeding success, or the number of fawns that each buck sired, in three distinct deer populations. One population was on the famous King Ranch in south Texas that is managed under strict trophy management guidelines where nearly half of all bucks are at least 4.5 years old. Another population was on a private property in Oklahoma managed under Quality Deer Management guidelines where about one-third of bucks were at least 3.5 years of age. The third population was on a public hunting area in Mississippi where few bucks survived beyond age 2.5.

On all areas, researchers extracted DNA from deer harvested, captured or found dead to recreate a “family tree” revealing which fawns were sired by which bucks. Surprisingly, on all three areas, they found that the average buck only sired 1-3 fawns annually, with the top breeder only siring 12 fawns over an 11-year period. Admittedly, researchers believed that they assigned paternity (you know, who’s your daddy?) to about half the fawns on each study area because not all fawns were captured. However, even doubling these figures would result in a low level of genetic contribution by an individual buck.

Initially, this finding was surprising, especially in the Texas and Oklahoma herds which featured high numbers of mature bucks. Previously, it was believed that mature bucks dominated breeding duties while suppressing breeding in younger bucks. However, when you consider the breeding ecology of the whitetail, this picture becomes easier to understand. Unlike a herding deer species like elk in which a dominant bull gathers up several cows and defends them against all comers, whitetails work solo. Whitetail bucks have to find a doe in or near estrus and then tend her for 24-36 hours just to have a chance of spreading his genes through her offspring. Given that in most whitetail herds about 75 percent of all does breed during a two- or three-week period, there are relatively few chances for an individual buck to pass on his genes. This task becomes even tougher when you realize that researchers also have recently discovered that multiple paternity occurs in around 25 percent of all sets of twin fawns. In other words, around one in every four sets of twin fawns has different fathers! This is the result of a doe being receptive to more than one buck during her 24-36-hour estrus period.

Given the above information, it’s not difficult to see the many challenges associated with impacting genetics in wild deer herds through culling. But, let’s assume that you could identify bucks with “bad antler genes” and that you could effectively remove all of them over a long period of time across thousands of acres of private land. Surely culling would provide positive benefits in this situation, right?

Luckily, this study was recently conducted by Dr. Mickey Hellickson in south Texas. Dr. Hellickson and his fellow researchers examined the impact of culling on two adjoining 10,000-acre sections of the King Ranch over an 8-year period. On one area (treatment area), stringent antler criteria were established for each age class of bucks from age 1.5 to full maturity. Essentially, a buck had to be a superstar at each age or it was removed. On the control area, existing harvest guidelines were continued which allowed for minimal harvest of trophy bucks. In total, over 130 cull bucks were removed from the treatment area, while less than 10 total bucks were removed from the control area. What did Dr. Hellickson find following 8 years of intensive culling on 10,000 acres? Absolutely no difference! That’s right, the antler size of the bucks remaining on the treatment area was the same as both the control area and the treatment area prior to culling.

The lack of any detectable difference in antler size was likely due to several factors including the size of the treatment area, duration of the study, and yearling buck dispersal. While few hunters have the luxury of hunting a 10,000-acre property, this is extremely small from a genetic standpoint. Likewise, while 8 years is a relatively long period of time to humans, it’s not even a blip on the screen from a genetic change perspective. Finally, given that previous studies have shown that around 70 percent of all yearling bucks disperse from the areas in which they were born and travel 2-5 miles to set up a new home range, it’s likely that many of the male offspring from the treatment area dispersed off the area while being replaced by young bucks from other areas. Regardless, the take home message is that hunters have about as much chance of impacting genetics in wild deer herds as they would altering the salinity of the ocean by adding a cup of fresh water!

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So, next time you and your hunting buddies discuss the merits of culling bucks to improve genetics, you will be armed with the latest Whitetail Science to help them make more informed decisions. Are there bucks that will never produce quality antlers? Sure, and there are even some legitimate reasons to take them, but genetic improvement is rarely one of them. Simply put, culling is generally used by hunters as an excuse to harvest more bucks and therefore is far more often a pitfall than a panacea.

Brian Murphy is an avid hunter, wildlife biologist and CEO of the Quality Deer Management Association (www.QDMA.com). He has worked exclusively in deer research and management for 25 years during which he has presented more than 600 lectures and authored more than 125 popular and scientific articles, book chapters and other educational materials designed for deer hunters and managers.