Next time you admire a bighorn sheep ram with full curls winding around the sides of his face – thank the big guy’s mom. It’s her nutrition that planted the necessary roots to help him grow that large, according to a recent paper by Kevin Monteith, an assistant professor at the University of Wyoming’s Haub School of Environment and Natural Resources and five other researchers.
Genetics played a role in his size, sure, but not as much as the food he ate and the health of his loving mother.
“The nutritional status of a mother and her ability to provide that offspring through gestation and weening sets the trajectory of a male not just through the first year of its life, but potentially life lasting,” Monteith said. “Even if the male gets healthier at 2 or 3, it won’t become the male that was offered the silver spoon early in life.”
The paper, called “Horn Size and Nutrition in Mountain Sheep: Can Ewe Handle the Truth?” was published in January in The Journal of Wildlife Management. It challenges the common perception that large horns – and also big antlers in other large game – are purely a product of genetics, and as a result can be eliminated from the gene pool because of hunting. It also raises the at-times controversial opinion that the best way to improve the health of females, and the health and size of the males, could be to hunt female bighorn sheep.
“Part of the thrust of the paper was to strive to communicate some realities,” Monteith said. “We usually think we need a lot of females because they reproduce and that’s how our populations grow. That is true, but they do much more than that.”
The issue with genetics
Monteith calls it our “hornographic culture.” It’s a term he coined, a play on words representing society’s love affair with big horns and antlers. It’s also often the driving force behind how hunters and wildlife viewers would like herds to be managed.
“Our culture and society has become fixated on large and elaborate hornlike structures,” Monteith said. “We care about them, but at the same time they are biologically important. They are used as tools in male-male combat, and they are used to indicate how robust an animal is.”
In a quest to produce larger horns, or at least maintain current sizes, people began looking at a bighorn sheep study from Alberta for answers. The work followed a small, isolated population where an unlimited number of ram tags were given out for any sheep that had horns that curled more than four-fifths of the way around.
The result was that most rams that reached that size were killed, which meant that smaller, slower-growing rams had more opportunity to reproduce and lived longer.
“In that population, they observed a 20 percent decline in horn size over time,” Monteith said.
The study essentially showed that hunting large rams out of a population over a period of years affected the presence of genes that made trophy-sized animals. The data was then used across North America to argue that removing big bucks, bulls or rams eventually creates smaller animals.
But it was more nuanced than that, Monteith said, particularly because bighorn sheep tags in places like Wyoming are very limited.
A series of studies he and his co-authors either conducted or reviewed from other researchers show that nutrition and mother health play a much greater role in how big a ram grows. Indeed, the best genetics in the country still won’t create a large ram if he or his mother doesn’t eat enough healthy food.
It makes sense, said Doug McWhirter, wildlife supervisor for the Wyoming Game and Fish Department in Jackson.
“Where you have limited quota hunting like our sheep harvest is done here, there’s no changes in horn size through time and no evidence of this deleterious impact of harvesting older age class rams,” he said.
Focus on the females
The main goals of a female bighorn sheep are to survive and reproduce – in that order. That means if they’re unhealthy or underweight, they won’t conceive.
If they do, the lamb is born smaller than its peers with healthier moms. And equally important, the lamb requires milk from its mother to survive for the first half a year. If the ewe is undernourished, her body won’t produce enough milk and the lamb will either die or stay little.
And they won’t likely ever grow as large as they may have otherwise.
Monteith used an unhunted population of bighorn sheep in the Sierra Nevada range as an example of this. The population had sheep in six different areas with similar genetics but different nutrition. Without fail, herds with the fattest females produced the largest males. Herds with the skinniest females made the smallest males.
“We’re a male dominated philosophical society and we keep overlooking the importance of females,” said Steve Kilpatrick, executive director of the Wyoming Wild Sheep Foundation.
Monteith admits that writing a paper focused largely on the importance of females may sound a bit out of place with one of his primary recommendations: consider hunting more ewes.
If ewes are so important, conventional wisdom goes, then wildlife managers should continue to protect them and allow only rams to be hunted.
But that ignores the other critical factor in growing big rams, he said, which is nutrition.
If a ram doesn’t have access to good food, he won’t grow as big. Similarly, if an ewe doesn’t have access to good forage, she won’t grow as big. Operating in a world where food is limited, the more ewes on the landscape, the more competition there is for groceries, Monteith said.
The professor cited the same Alberta study that tracked a bighorn sheep herd for about 10 years after all ewe hunting stopped. While the herd population nearly doubled, the number of rams available to hunt – those with a curl that went four-fifths of the way around – stayed the same.
“The proportion of males that were legal went from 66 percent and dropped down to 34 percent after they stopped shooting females,” Monteith said.
There were simply more animals on the landscape with less food to go around.
Neither McWhirter, the Game and Fish biologist, nor Kilpatrick were surprised by the findings. They understand the role nutrition plays in all mammals on the landscape.
Kilpatrick likened habitat – essentially the food available to eat – to the foundation of a house.
“We drive around the countryside and we see this beautiful log house with a gorgeous fireplace and surrounding setting and we drool at that log house thinking I wish that was mine, but do we stop to think, what is the foundation under that house? The cement and rebar and how well is the draining system?” he said. “That is the habitat that underlies every wildlife population out there. The rebar and cement is equivalent of the habitat, what keeps a wildlife population upright.”
Ewe hunting is still controversial in some hunting and nonhunting circles. It has only been legal in Wyoming since 2009. But the times ewe tags were made available, they’ve been popular, McWhirter said. The first year they were issued, in 2012, 600 Wyoming residents applied for 15 ewe/lamb tags in one hunt area.
Monteith’s paper did not delve into the issues bighorn sheep have with disease — pneumonia outbreaks have decimated some herds – but if nutrition improves in males and females, it’s only logical that better nutrition could improve their ability to tolerate disease.
“If you want big males, you need mature or older animals for them to possess large horns,” he said. “And those horns or antlers don’t come for free. They require a lot to grow.”