Stories in South Dakota

September Nature Notes

For many mammals, fall is the time for courtship.

Closeup of a pronghorn in a field of golden grasses.
Pronghorn Pronghorn don’t have antlers—they have horns with a forward-facing fork, or prong, as their name suggests. © Harvey Payne/TNC

Spring is the season most often associated with courtship, but for many mammals, that’s an activity for fall. Their offspring do best if born soon after winter has ended, when they have time to grow before the return of harsh weather. As a result, mating must take place in the fall for births to occur in the spring after months of pregnancy.

This fall breeding season for hoofed mammals is called the rut. This is the time of year when antlers and horns become essential—males use their headgear when they compete for females. Spectacular clashes can occur; bull elk, for example, lock antlers in a contest to see who will prevail and get to mate with a nearby female. The rut begins at different times in the fall for different animals. Pronghorn are among the first; their rut begins in mid-September and can last well into October.

Two pronghorn stand in a field of golden grasses.
On the Plains This uniquely North American mammal can still be found in South Dakota. © Bob Gress
A pronghorn stands facing away from the camera and turns its head to look back over its shoulder.
Unique horns Unlike antlers, the horns on a pronghorn are not shed and regrown each year. Only the outer sheath is shed and regrown. © Michael Forsberg

Pronghorn don’t have antlers—they have horns with a forward-facing fork, or prong, as in their name. Antlers are bone and so are horns, but unlike antlers, horns aren’t shed. Horns have a bony core that is covered with a nail-like sheath; in pronghorns, that sheath is formed by fused hair that grows to become the outermost tips of the horn. Both males and females have horns, but a female’s horns are much smaller, typically not forked and only a few inches long (a male’s horns can be a foot or longer in length).

The horns are mostly for show but can become weapons if two males are closely matched. Bucks establish territories in March, long before the rut begins. They select the best grazing lands that will attract does—many does—and ultimately a harem that they will defend against other males in September. Usually, all that is needed is a snort, a stare or a brief chase to discourage a potential rival. But animals of similar fitness may come to blows, clashing their horns until one of them leaves. Young males or old bucks past their prime are rarely able to claim a harem.