Pronghorn

The pronghorn looks like an antelope and is often called one, but it is something rarer: the last survivor of a family of animals found nowhere else on Earth, and an athlete built for a race that ended 12,000 years ago.

Overview

Pronghorn live in the wide open country of western North America — shortgrass prairie, sagebrush steppe, and high desert — from the Canadian prairies to northern Mexico. They need long sightlines and room to run, and they are among the few large mammals that can make a living on sagebrush, a shrub so bitter and resinous that most animals leave it alone.

Built to run — and keep running

The pronghorn is the fastest land animal in the Americas, reaching 88–98 km/h. But raw top speed is the cheetah’s specialty; the pronghorn’s is endurance. It can cruise at 60 km/h for more than 20 km without stopping, a sustained pace no other large land animal comes close to.

The body is over-engineered for it:

• An oversized windpipe, lungs, and heart to move huge volumes of oxygen.
• Light, hollow bones and long, slender legs with extra cushioning in the pointed hooves to absorb the pounding.
• Large protruding eyes set high and wide on the skull, giving roughly a 320-degree field of view and vision about eight times sharper than a human’s — a pronghorn can spot movement 6 km away and start running long before a predator is close.

Evolutionary biologists explain the excess with a “ghost of predators past”: North America once had a cheetah-like cat and other fast pursuers. They died out at the end of the Ice Age, but the pronghorn’s adaptations to outrun them stayed, because there was never any cost to being too fast.

The strange horns

Pronghorn “horns” break the usual rules. Like true horns they have a permanent bony core covered by a keratin sheath — but the sheath is branched (the forward-pointing “prong”) and is shed and regrown every year, like a deer’s antlers. No other animal has horns that both fork and moult. Both sexes grow them; the bucks’ are much larger.

Behaviour and life cycle

Pronghorn form large mixed herds in winter and break into smaller groups in summer, when bucks defend territories or harems. They communicate danger by flaring the white rump patch, which flashes visibly across the plain and can be seen — and smelled, from a scent gland it exposes — by other pronghorn far away.

Females usually give birth to twins after an eight-month pregnancy. Newborn fawns lie motionless and nearly scentless in the grass for their first weeks, and by a few days old can already outrun a human.

Threats and conservation

The pronghorn is listed as Least Concern, with a stable overall population, but that hides an important problem: fences and roads. Because pronghorn go under obstacles rather than over them, standard livestock fencing fragments their range and, critically, severs the long seasonal migrations some populations make between summer and winter range — including the 240 km “Path of the Pronghorn” in Wyoming, the longest land-mammal migration in the contiguous United States. Wildlife crossings, fence modifications, and protected migration corridors are the main conservation tools. The Sonoran pronghorn of the Arizona–Mexico desert is a separate, Endangered subspecies down to a few hundred animals.