The horn and antler sizes on big-game trophy animals have grown slightly smaller over the past 100 years, with evidence pointing to the selective harvest of males as a possible cause, a new study has found.
The findings were released this month by six researchers from the University of Montana, Idaho State University, Arizona Game and Fish and the California Department of Fish and Game.
The team reviewed 22,000 Boone and Crockett Club records and found a roughly 2 percent decline in the size of horns and antlers in 25 trophy categories of North American big-game species. The decline has occurred over the past 108 years.
“The Boone and Crockett Club is the oldest conservation club in the U.S. and the second oldest in the world,” said Paul Krausman, the Boone and Crockett professor of wildlife conservation at UM. “They maintain a record of horns and antlers and it’s the biggest record we know of.”
Krausman said the Boone and Crockett records – kept at the club’s headquarters in Missoula – reflect the overall and long-term health of North America’s wildlife populations. The record is extensive and dates back to around 1905, though it had never been analyzed before now.
The record includes 15,778 listings for antlered game and 6,526 for horned game. The study found the reduction in horn and antler size had occurred in 11 of 17 antlered species and three of eight horned species.
“The decrease is statistically significant – it really is a change,” said Krausman. “But biologically, it doesn’t make a whole lot of difference.”
Several species protected by more conservative hunting regulations, including bighorn sheep and bison, did not exhibit the same reduction in horn size. Pronghorn showed a significant increase in horn size over the last century, Krausman said.
Krausman attributes the horn and antler reduction in other species to the focused harvesting of males. The study suggests that, over time, it has lowered the age structure, allowing fewer animals to reach trophy status prior to harvest.
“The main thing that supports the decrease was harvest, but that doesn’t mean hunting is ruining the genetic stock in these animals,” Krausman said. “Conservation is benefited so much by hunting for all it does. It far exceeds this miniscule decline in horn and antler size.”
Historically, Krausman said, conservationists recognized the need for laws to protect large, hoofed mammals across North America from unregulated hunting in the late 19th and early 20th centuries.
Leading the conservation effort was President Teddy Roosevelt, who in 1887 founded the Boone and Crocket Club. The club sought to “work for the preservation of the large game of this country, and, so far as possible, to further legislation for that purpose, and to assist in enforcing the existing laws.”
The club also looked to establish a baseline against which future trends in the size of trophy animals could be compared. Early measurements included a simple look at the skull’s length or the longest antler or horn.
But in 1949, a committee formed to develop a standardized method of measuring large North American mammals. Adopted in 1950, the system remains the universal standard for quantifying antler and horn size.
“We took that 108-year-old data set to determine if horns and antlers were changing,” Krausman said. “We looked at those in relation to habitat, climate change, hunting pressure, sociological issues and genetics.
“After we looked at everything, we found no shift in some species that are conservatively harvested. But in other species, they did indeed show decreases in horn and antler sizes.”