Can Trophy Hunting Alter Wildlife Genes?

Short answer: In small enclosures, yes. In the wild, only in theory.

For our purposes, let’s define “trophy hunting” as selectively shooting only the biggest males of a species year after year. If that’s done, what happens? An infamous article in Newsweek  (Jan. 12, 2009) claimed “trophy hunters” were degrading the gene pools of deer, sheep, and elephants by selectively killing the herd’s biggest males.

The evidence, however, then and now, argues that it’s nearly impossible for hunters to alter the gene pools of free-ranging wildlife unless these criteria exist:

• The herd lives in a small, geographically isolated area cut off from other herds.
• The herd is heavily hunted.
• Hunters, by choice or by rule, shoot only males carrying the largest horns or antlers.

Those criteria seldom occur jointly. In most cases, natural variables and obstacles protect gene pools from unnatural selection. Those factors include:

• Female wildlife contribute half the genes in their newborns, and there’s no way to reliably target or protect “top” females to capitalize on their age, genetics, or mothering traits.
• “Trophy hunters” make up a small segment of most hunting populations. Many hunters shoot the first legal male or first “satisfactory” male that offers a shot.
• The oldest or biggest bucks, bulls, and rams aren’t necessarily the herd’s most successful breeders.
• Herds or individual animals often disperse and migrate, sometimes into unhunted areas, forever adding or subtracting to a herd’s gene pool.
• Injuries, disease, starvation, and predation constantly change a herd’s composition.

In addition, many of those factors and others are hard to measure or assess. Bronson Strickland, a wildlife professor at Mississippi State University, also notes the varied breeding habits of big game animals further complicates comparisons. Elk, sheep, and pronghorns are “harem breeders,” while whitetail deer pair off for a day or two. Even so, individual bucks, bulls, and rams of breeding age often cut in on receptive females when the dominant male is absent or distracted.

And without tests to assess forage quality and availability, biologists can’t say with certainty whether it’s genes or nutrition that is increasing or decreasing antlers, horns, or body sizes. Forage availability and its nutritional values differ annually and seasonally. Hunters might assume a buck’s antlers grow consistently larger each year between ages 2 and 7, but poor forage doesn’t always allow it. As an early gamekeeper, William Twiti noted in “The Art of Hunting” in 1327, “The head grows according to pasture; good or otherwise.”

False Assumptions
So, where do we get these ideas that hunters can—or do—affect wildlife gene pools? Much of that 2009 Newsweek article was based on a 2003 research article, “Undesirable evolutionary consequences of trophy hunting,” about bighorn sheep on Alberta’s Ram Mountain. That study, which remains ongoing, initially found that shooting trophy rams reduced average horn sizes in the herd’s age classes.

Most wildlife biologists dismissed the findings, noting that Ram Mountain was a unique situation. It covers only 15 square miles, its sheep are semi-wild and isolated from other herds, hunting wasn’t restricted in the decades preceding 2003, a rams’ horns had to carry at least a 4/5 curl those years, and ram numbers varied annually from eight to 61 in the preceding decades. Ram Mountain’s sheep are also ear-tagged, and some are radio-collared. They’re corralled annually for scientific assessments, which provide data on each animal’s age and pedigree.

“Those are not conditions you find for most North American wildlife populations,” said Jim Heffelfinger, wildlife science coordinator for the Arizona Game and Fish Department, and a research scientist at the University of Arizona. “Ram Mountain’s sheep are managed like a captive population. Soon after that 2003 paper came out, managers restricted the harvest to full curl, which eliminated intensive selection. No one should extrapolate anything from that herd across North America, especially not for elk, deer, or other wildlife species.”

Heffelfinger references a 2019 study by Tayler LaSharr at the University of Wyoming that evaluated 25,000 harvest records for male bighorn sheep spanning 72 hunt areas in nine U.S. states and one Canadian province from 1981 through 2016.

“After addressing the effects of age and environment, horn size didn’t change in 50 (70%) of those units; but it increased in six (8%) and decreased in 16 (22%),” Heffelfinger said. “In the units where horn size declined, only seven had hunting conditions with potential for evolutionary change. That means 78% of the continent’s sheep units improved or didn’t change. That doesn’t indicate a widespread problem. Most units have low or no potential for harm, and we can change any possible problems through management. In Arizona, we offer 116 ram tags to hunt 6,000 bighorn sheep. Think of all the conservation dollars and opportunity hunters get while harvesting less than 2% of the population.”

Culling’s Failed Hopes
Hunters, however, also add to false claims of selective gene manipulation, but from the opposite spectrum. By culling “inferior” bucks or bulls, many hunters and wildlife managers have long hoped to genetically engineer bigger antlers. Those efforts always end in futility.

“Shooting small yearlings while protecting mature males to ‘improve’ the gene pool fails for the same reasons that shooting mature males while protecting young ones fails to ‘degrade’ the gene pool,” Strickland said. “There’s too many uncontrolled variables. Pens are the only places where you can manipulate genetics, because you must know the age and pedigree of each animal, control their nutrition, monitor their health, control which ones breed, and then choose their partners. You’ll never see those conditions or control them in the wild.”

Donnie Draeger, a biologist at the Comanche Ranch in Texas, worked with Texas A&M University on an aggressive, large-scale culling experiment on the ranch’s wild deer from 2006 to 2019. Using helicopters and gun-propelled drop nets, the researchers caught, aged, assessed, and strategically culled yearling bucks to learn if they could cause an evolutionary change in antler traits.

Draeger presented the study’s results at the annual Southeast Deer Study Group meeting in February, 2019, in Louisville, Kentucky.

In all, the research teams captured 2,937 bucks, some more than once, and “sacrificed” 1,333 that didn’t have at least six points as 1-year-olds, or eight points when 2 or older. Only 6% of the bucks carried six or more points as yearlings. The “sacrificed” bucks were donated to food programs. Draeger said the researchers also used DNA samples to match 963 deer to their sires.

They conducted three simultaneous studies for comparisons:

• An intensive cull on 3,500 acres where bucks of all ages were culled based on antler criteria,
• A moderate cull on 18,000 acres where males age 3 and older were culled,
• A “control” area of 5,000 acres where no bucks were culled.

Your Gut Can Lie
“All that work, all that culling; it didn’t do any good,” Draeger said. “The average score of the standing ‘crop’ of bucks did not improve; it did not change. That shocked me as a hunter and guide. I thought we were making a difference. Most deer I saw had the ear notch, which told us we had our hands around that herd. My gut said we were having an impact. Well, empirical evidence doesn’t lie, but my gut apparently does.”

Draeger said the study’s early results looked promising until they analyzed the “control” pasture. “The bucks there were doing the same thing; achieving the same results,” he said. “That suggests the improvements we saw were environmental, and had nothing to do with genetics. It’s the same ol’ thing: A high tide raises all ships. If you have a culling agenda, but you don’t have a ‘control’ pasture for comparisons, you don’t have anything.”

Draeger said the study confirmed that buck and doe appearances are deceiving. “We’ve known a long time that you can’t selectively cull does,” he said. “They all look alike. Based on appearances alone, we don’t know what antlers they’ll produce in their offspring. Well, the same thing can now be said for bucks. What they display on their heads is not correlated enough to predict what their offspring will be, or what they’ll be themselves down the road.”

One buck, for example, scored 190 inches on the Boone and Crockett Club’s scale as a 6-year-old in 2010. Later, one of its offspring measured only 117 inches at age 6, and another measured 110 inches at age 5.

“So, what does that tell us about culling?” Draeger asked rhetorically. “The best reasons to cull a herd is to control the population, and improve its food quality and availability. If you see improvements in antlers and body sizes, it’s probably not a genetic change.”

What About APRs?
If it’s impossible to harm or improve a herd’s genetic profile through hunting, how come some antler-based restrictions can “high-grade” a herd’s young bucks each year? That is, some antler-point restrictions, or APRs, remove bucks that would likely produce the herd’s biggest racks two or three years later.

Those restrictions and their outcomes don’t affect the gene pool, Strickland said. “All you’re doing is changing the composition of that herd’s annual buck crop, not its genetics,” he said. “As soon as you drop the APR, the herd will go right back to where it was before.”

Strickland said the number of antler points on a rack often doesn’t correlate with age, and yearling bucks can carry anything from 2-inch spikes to 10-point basket racks. Mississippi replaced its original APR years ago because it exposed bucks to harvest if their rack carried four or more points. Bucks in Mississippi’s soil-rich Delta region must now have a minimum 12-inch inside spread or a 15-inch main antler beam. Bucks elsewhere in Mississippi must have at least a 10-inch inside spread or 13-inch main beam.

Strickland said time provides the true test of genetic change. “If we could kill off all those ‘bad 8-point genes’ by shooting every 8-pointer in the herd, you’d never see 8-pointers decades from now,” he said. “Yes, some years you might shoot so many 8-pointers that all you see by the end of the season is 10-pointers. But next fall, you’ll just start over, shooting 8-pointers. A 130-inch 8-pointer is a standard mature Southern buck. That’s not going to change.”

On the opposite extreme, hunters in Wisconsin, Michigan, and Pennsylvania commonly shot 90% of their states’ annual buck crop when those 1½-year-olds were carrying their first spikes or fork-horns. Some hunters claimed the heavy mortality rate “shot out the herd’s genetics,” but indiscriminate shooting is just another version of random selection.

“They weren’t selecting for any trait,” Strickland said. “They were just taking the first antlered buck that offers a shot. Random selection won’t change any genetics.”

Nature Unwinds Artificial Springs
Perhaps the most intentional attempts to alter wildlife genetics occurred in some Southern states where landowners used artificial insemination or captive breeding to selectively produce big bucks. Some of those “test-tube” bucks ended up in the wild, purposefully or accidentally.

“We’ve all seen some of those Frankenstein deer,” Heffelfinger said. “They can produce 150- and 170-inch yearlings. Anything is possible when you control every aspect of when and what they eat and breed. But none of that is sustainable in the wild.”

Professor Steve Demarais, a colleague of Strickland’s at Mississippi State University, said such results would be miracles in the wild.

“When you roll the dice in Yahtzee, the best you can get is straight 6s,” Demarais said. “Now consider the odds of getting all 5s and 6s when you roll 10 or 20 dice at once. Those are about the odds of producing a Boone and Crockett buck in the wild, but it happens. In a pen, generations of selective breeding increase the number of 5s and 6s you throw.”

Once a mega-buck goes free on the landscape, however, nature quickly swamps its artificially packaged genes. “When you manipulate genetics, it’s like winding a spring tighter and tighter,” Demarais said. “As soon as you put that tightly wound spring—that big, excellent buck—out in the wild, those genetics unwind real fast when he starts breeding normal does.

“Let’s say you start with a buck that’s 100 on the genetic scale and wind his spring to 200. He breeds a doe carrying the genes of a 50, and she produces deer that are 112.5 on average. Then that 112 buck breeds another doe that’s 50, and the offspring are about 82. That 82 breeds another 50, and within four generations what have you changed?

“That’s just a hobby,” Demarais continued. “That’s not wildlife management.”

Feature image via Matt Hansen.