Autumn heralds a dynamic phase in the annual cycle of Colorado’s wild, hoofed mammals—the fall rut, or breeding season. The pronghorn season is the first and the earliest, making September one of the best times of year for pronghorn-watching.
Pronghorn bucks will defend territories from March to October, defining their space by marking tall vegetation with urine and gland secretions, leaving piles of feces, and making scrapes in the ground. They will challenge intruding bucks with vocal displays, stare threats, approach and chase behavior, and occasional battles.
By late August, bucks begin to gather does into harems that they will maintain through September. Wildlife watchers at this time of year will notice pronghorn in groups of a single buck with several does and any fawns born that year.
After the end of the rut, another change happens to pronghorn—they lose their horns. The headgear of the pronghorn is unique among Colorado mammals. Like the horns of sheep and goats, the horns grow as a sheath over a bony core which is part of the skull. Like the antlers of a deer, they are shed every year. Underneath the old sheath, a new one is developing which will be fully grown by mid-summer. Also like sheep and goats, both the female and male pronghorn have horns, though those of the female are small, unforked and inconspicuous. (Among deer, elk, and moose, only males have antlers.) Another quirky thing about pronghorn horns—they are made of masses of fused hair.
Pronghorn are animals of prairies, mountain parks, and western shrublands. Watch for them along highways through open country across much of the state. If you see pronghorn, don’t approach them. They have telescopic vision and are extremely wary. They will see you coming a long way off and hightail it and all you’ll get to watch is their white rumps running off across the grass.