Their upper body and back is pale tan to reddish tan, their sides, belly, inside of the legs and their rumpare white. They have two broad white bands across their throat. Bucks have a black band on the snout that extends from the nose down to a black neck patch. Both sexes have horns that are unique among the hoofed animals because the outer sheath of the horn is shed annually. The horns are black and curve backward and inward at the tips. They are between 12 and 20 inches long in males but, usually not more than about 4 inches long in females. The horn of males have a forward pointing, short branch called a “prong”, hence the name pronghorn. Pronghorns are somewhat small compared to other hoofed mammals; males weigh between 90 and 140 pounds 41-62 kg), females between 75 and 105 pounds (34-48 kg). Their large, white rump patch can serve as a danger signal when the long, white hairs are erected as danger is detected. This white patch can be seen from long distances. Their coat includes long outer, hollow hairs which provides great insulation against severe winter cold.
Pronghorns range from the southern Prairie Provinces of Canada (Alberta and Saskatchewan) east to western North Dakota, south through the intermountain Western U.S. through western Texas and Arizona to northern Mexico.
They are generally found on grasslands, shrub steppe, and foothills. They seem to prefer rangeland with vegetation less than 2 feet in height and wide open, expansive range. They are often found in low shrubs such as sagebrush, and grassy vegetation in arid regions with less than 10 to 12 inches of snow on the ground in the winter. This may lead them to upper, wind-swept slopes in the winter, or fairly long migrations between summer and winter range. They seem to need water within about 4 miles.
In the winter, northern populations depend heavily on browse, especially sagebrush. In the summer, forbs are the most important; they rarely utilize grasses. Southern populations use more forbs and less browse.
Their daily activity pattern varies seasonally. Alternating periods of feeding and resting occur throughout day, with fairly continuous feeding in early morning and late afternoon, and longer rest periods at night. An Idaho study found that major summer feeding peaks were in early morning and late evening; they spent 30% of the day feeding, and 65% resting or loafing. Their home range varies between 0.2-0.6 km2, but an Idaho study found summer home ranges averaged about 2000 ha. Home range of yearlings was 2 to 5 times greater than adults. Large herds form in the winter but disperse in spring and form separate bachelor and female-fawn groups in spring and summer. Males associate with females in late summer and early fall. In Idaho, pronghorns typically migrate to lower elevations in winter and move back to the heads of mountain valleys in the spring. Pronghorns have some unique adaptations for their existence in open country. They have tremendous vision accommodated by an eyeball up to 1.5 inches in diameter (the size of they typical horse eye). The rods and cones of their eye are spread on a horizontal plane providing for excellent sight on a flat plane corresponding to the horizon. Most mammals’ rods and cones are concentrated in the center of the eye. This does not provide for good eyesight above them, but are known to detect movement up to 4 miles out toward the horizon. Their heart, lungs and trachea are 2 to 4 times larger than similar sized ungulates (such as goats). Their blood is very rich in hemoglobin and their muscle tissue is densely packed with mitochondria . Their leg bones are estimated to be twice as strong as cow bones, which are twice as thick. Obviously, their bones are very dense. All of these adaptations allow them to be the fastest mammals in North America. They have been clocked at nearly 70 mph and they can obtain and maintain speeds of 30 to 45 mph for fairly long distances. The dense bone prevents injuries while running at fast speeds over very rough terrain, and certain the large heart and “rich” blood accommodate their stamina. Its been estimated that if a pronghorn raced a cheetah (the fastest known mammal), the cheetah would win in a short sprint, but the pronghorn would quickly outdistance the cheetah after the sprint. Pronghorns, at times seem playful, and have been known to race along vehicles driving on roads through their habitat, and even chasing their most common predator, the coyote. Bobcats are also predators of young. Historically, pronghorns were extremely numerous throughout the west, but agricultural development, cattle grazing and construction of fences drastically reduced their populations. Many pronghorn populations have not adapted to fences and their movements, and even seasonal migrations, have been blocked by fences. Some pronghorns do crawl under fences.
Pronghorns breed from mid-September to early October in their northern range, from late July to early October in the south. gestation lasts 240 to 250 days in northern range, and is shorter in south (e.g., 210-225 days in Texas), however, implantation of the fertilized egg does not occur for about a month after breeding. Births occur earlier in their southern range than in north; for example, in April and May in Texas, but late May and early June in the northern Rockies. Adult females usually give birth to twins but yearling females may produce only a single fawn. The unspotted young are weaned by 4 months, but continue to follow mother during first winter. High mortality in young is common, mostly from predation. In Idaho, a ratio of 75 fawns to 100 does is considered good. Males become territorial in mid-summer and “round up” harems of females, often up to 20. Territorial bucks mark their territorial by rubbing scent glands on the side of the neck behind the jaw on vegetation, and possibly by pawing the ground and urinating and defecating on the paw marks. They defend their territories with frequent loud “snorts”, various ritual displays, and occasionally battles and incredibly speedy chases of intruding bucks. In the wild there are few events more spectacular than two territorial bucks chasing each other at incredibly high speeds.
Important State References:
Autenreith, R.E. and E. Fichter. 1975. On the behavior and socialization of pronghorn fawns. Wildl. Monog. 42:1-111.