Your girlfriend or wife may tell you that size doesn’t matter, but apparently, it does for Bighorn sheep. A recent study conducted by a group of researchers has revealed that the size of horns on bighorn sheep can have an interesting effect on female reproductive success.
The study was led by Ph.D. candidate Samuel Deakin from the University of Alberta. Deakin and his team studied a whopping 45 years’ worth of data related to the bighorn sheep population on Ram Mountain.
Ram Mountain, located 30 kilometres east of the Canadian Rockies, is no place for mere mortals.
The mountain range is about 1700 to 2200 meters in altitude. While Ram Mountain features beautiful snow-covered peaks and vegetation, the weather there is unpredictable and dangerous.
But for the bighorn sheep in the area, Ram Mountain is home. Deakin’s findings are based on the Ram Mountain study that began in 1971. Since then, more data has been collected on these sheep, including population size, weight changes, reproduction, horn growth, and more.
Deakin had an absolute treasure trove of information to comb through.
Based on past research, it is already known that female bighorn sheep with larger body mass are more successful mates. Because of this, these female sheep tend to birth lambs earlier.
But Deakin’s research has found that the reproductive success of female bighorn sheep is also tied to horn size, not just body mass.
“Thus, larger horns correlate with higher reproductive fitness in both male and female bighorn sheep,” Deakin told Rocky Mountain Outlook.
For male bighorn sheep, this observation makes sense. A male bighorn sheep with larger horns is more likely to win a fight with another male with smaller horns. By winning, this male has a greater selection of female bighorn sheep to mate with.
On the other hand, the relation between horn size and reproductivity in female bighorn sheep isn’t as obvious. But Deakin believes a gene tied to a female’s horn size may influence reproductivity.
A male bighorn sheep with large horns passes down this gene through breeding. Long story short, a female lamb that inherits this gene will have larger horns and greater reproductivity.
To put things into perspective, Deakin found that long-horned females had their first lamb at the age of three. In comparison, short-horned females didn’t have their first lamb until the age of five.
When it comes to Ram Mountain’s bighorn sheep, size really does matter. But trophy hunting of male bighorn sheep is hurting this population.
“Trophy hunting and selective harvesting of males based on horn size couple deplete the inheritance of traits associated with greater female reproductive fitness in bighorn sheep,” said Deakin.
Hunters targeting male sheep with big horns reduce the number of offspring that receive this gene, including female sheep. More often than not, these males are killed before they make it to breeding season.
As a result, females have been experiencing a reduction in horn size over the years and are reproducing at a slower rate.
While Alberta’s bighorn sheep population is considered stable, Deakin fears trophy hunting will have an irreversible evolutionary impact on these majestic sheep.
In the last 40 years, the horn size of the Ram Mountain bighorn sheep population has decreased by two to three centimetres. This number is only going to increase with time. If something doesn’t change now, we will have a conservation issue in the future. Why wait?
