Size:
Pronghorn are the smallest of North American ungulates. They weigh between 75 pounds for a small female or doe and up to 150 pounds for a buck.
Diet:
Pronghorn are mixed foraging herbivores, consuming both herbaceous vegetation and woody plants. Despite having high-crowned teeth, only around 12% of their diet is grass. During the summer, they primarily feed on young forbs. However, due to their limited ability to dig through snow to access food, pronghorn rely heavily on Sagebrush (Artemisia tridentata) in the winter months. Sagebrush can constitute up to 60% of their diet during this period, distinguishing pronghorn as one of the few animals that actively forage on this plant in snowy seasons.
Breeding:
The mating season for pronghorn is September and October. Unlike many of our ungulates, breeding often occurs en route to or on their winter range. Even more unique to ungulates is that they shed the sheaths from their horns after the rut! Pronghorn are among the more fecund ungulates, regularly producing twins and, on occasion, triplets. Much like elk calves, pronghorn fawns demonstrate a strong “fawn response” during their first two weeks of life.
Population:
The GYE population of pronghorn relies on a number of migratory herds. Both the Paradise Valley herd and the Sublette herd have between 500-800 individuals during any given year. A recent harsh winter dropped the sublette herd by 88% and a fence trapped another 45 individuals the following summer, causing the population to drop and stunting its recovery. Estimates of pronghorn county-wide run just over a million, with 60% of those located in Wyoming. This is down for the 35-100 million that once roamed the Americas
America’s Fastest Land Mammal:
One of the fastest mammals in the world, the pronghorn is an animal evolved purely for speed. Reaching speeds up to 60 miles per hour, this speed demon coevolved alongside the American cheetah. This spurred an evolutionary arms race, a back-and-forth of which animal could be the fastest. The pronghorn won by default, but not before sacrificing everything that wasn’t speed-related. This evolution went so far that the pronghorn's morphology is such that they cannot jump more than a few feet (impala can jump more than 10 feet for comparison). Tragically, they also lost their dewclaws in the effort to outrun the cheetah. This may seem like a minor loss, but in the deep snow of Wyoming, this has led to mass casualty events during harsh winters. The sublette herd in the southern GYE lost nearly 90% of individuals in the winter of 22/23.
Evolution:
Pronghorns are a distinct group native exclusively to North America, having originated in the early Miocene period, roughly 20 million years ago. Despite their long evolutionary history, they never expanded into South America, likely due to ecological barriers such as dense forests that limited their dispersal.
Early members of the pronghorn family, scientifically known as Antilocaprids, exhibited a remarkable diversity in head ornamentation. While some species bore a single horn, others displayed large, moose-like paddle-shaped structures. Interestingly, one genus developed asymmetrical horns, a unique trait within the group. Additionally, variations extended to horn coverings: some had horns sheathed in skin, as indicated by rough bone textures, whereas others possessed keratin sheaths similar to those found in modern pronghorns.
Key anatomical features defining the pronghorn clade include large eyes positioned far back on the skull, an enlargement of the auditory bulla relative to their ancestors, which likely enhanced their hearing capabilities, and the absence of digits 1, 2, and 5 on their limbs. This digit loss means pronghorns do not have dew claws, distinguishing their limb structure from many other ungulates.
Underrated survival story:
100,000,000 million down to as low as 13,000 in 1915, now back up to 1 million
