Antilocapra americana
pronghorn

Antilocapra americana occurs from southern Alberta and southern Saskatchewan, Canada through the western United States to Hidalgo, Baja California, and western Sonora, Mexico.

The pronghorn is found from sea level to 3353m in grassland and desert.

Antilocapra americana, the only species within the family Antilocapridae, is unique in its form. Its horns are distinct; they are indeed pronged and consist of a permanent bony core covered by an annually-shed keratinous sheath. The long, woolly undercoat is covered by coarse, brittle hairs. This animal is reddish-brown or tan above and white below. The neck bears a short black mane and two white stripes across its anterior portion. The rump is white. Males have a black mask and black patches on the sides of the neck. Their horns extend past the tips of their ears. Females lack these black markings and often bear horns; these are rarely pronged and are not longer than the ears. The horns of males average 250mm, those of females average 120mm. Head and body length ranges from 1000 to1500mm, tail length from 75 to 178mm, and shoulder height from 810 to 1040mm. Males are, on average, 10% larger than females. Females usually have four mammae, but six have been recorded in some individuals.

Antilocapra americana can reach speeds of over 86 km per hour, making it the fastest New World mammal. Pronghorn are both diurnal and nocturnal. They show minor activity peaks just after sunset and before sunrise. Daily movement is resource-dependent; in the spring and summer pronghorns move 0.1 to 0.8 km each day as they forage. Fall and winter foraging require that herds cover 3.2 to 9.7 km each day. Deep snows may cause herds to shift their ranges as much as 160 km.

In the fall and winter pronghorn form large, loose herds of up to 1000 individuals of all age and sex classes. During the spring and summer the herd breaks up into smaller groups segregated by sex. At this point males over 3 year old compete for territories and female herds travel freely between territories. Territories are 0.23 to 4.34 square km, contain a water source, and are often bounded by physical barriers thought to help the male keep female groups inside. Males scent-mark their territories. Intruding males are challenged with an intense stare, signifying aggression. If the invader continues to trespass, an injurious fight may ensue. Bachelor males form groups that wander about in the "no man's land" between territories. They often chase and harass both receptive and non-receptive females. The territories of the dominant males actually serve as a haven to the females, protecting them from bachelor males and eliminating competetion for the best food sources between females and bachelor males. After the mating season, horn sheaths are shed and hierarchical distinctions become unclear. The loose aggregation reforms.

Several vocalizations and visual signals are common among pronghorn: Calves bleat when separated from their mother, mothers grunt when seeking their calves, males roar during fights, males and females blow through their nostrils when angered, and the hairs of the white rump patch are erected in warning.

As the pronghorn is fairly widely distributed over several habitat types, its diet depends on local resources. A 1964 study estimated the percentage of the entire species found on various vegetative communities and found the following: Sixty-two percent lived on grasslands, 37% on grassland-brushland (mostly bunchgrass and sagebrush), and 1% on desert. Browse makes up approximately 80% of the winter diet of northern pronghorns. When browse is not available these animals eat winter wheat. Grassland does not provide enough nutrition for northern pronghorn in the winter. Forbs are the main food source in the summer; in dry years browse is eaten in summer as well as in winter. Southern pronghorn eat more forbs and less browse than northern proghorn. A study of Kansas pronghorn estimated that cactus is 40% of the diet, grass 22%, forbs 20%, and browse 18%. Antilocapra does not drink free water unless the forbs and other vegatation it consumes are low in water.

Pronghorn will dig through snow with their forefeet to obtain vegetation in the winter.

The pronghorn is of economic importance for several reasons. It is the second most popular game animal in North America. In addition, its ability to consume noxious weeds makes it important in range management. One researcher estimated that one cow eats as much as thirty-eight pronghorn. Thus, it may prove economically beneficial to convert selected areas of pastureland to rangeland from which pronghorn can be harvested .

The Mexican populations of the Pronghorn are listed as CITES Appendix I. Antilocapra americana peninsularis and A. a. sonoriensis are listed as U.S. ESA and IUCN Endangered. It is estimated that the size of the pronghorn population prior to the arrival of Europeans was 35 million. These animals were distributed from eastern Washington and southern Manitoba to Baja California and northeastern Mexico. The 1920 count estimated that fewer than 20,000 pronghorn remained. Conservation attempts and proper range management have increased this number to 500,000 in the United States and Canada, but the Mexican population, victim to poaching and habitat destruction in the forms of oil explorations and strip mining, remains dangerously small. Approximately 1200 animals remain.

Populations of pronghorn have been mixed through transplantation. More than 4000 animals were transplanted in New Mexico between 1936 and 1957. Also, grassland herds in southern Arizona received tranplants from northern Arizona, and herds in Washington were transplanted from Oregon and Nevada. As a result, distinctions between subspecies are unclear over much of the pronghorn's current range. The taxonomic position of the pronghorn has long been debated. Its placement in the family Antilocapridae is based upon several characters that set it apart from the bovids, such as the annual shedding of its horn sheaths. Some mammalogists argue that distinctions based on sheath-shedding are invalid and that Antilocapra belongs in a subfamily within Bovidae because there is at least one species within each of the subfamilies of Bovidae that sheds the outer sheath of its horns. However, the way in which Antilocapra sheds its horn sheaths is very different from the way in which bovids shed theirs; bovids shed their sheaths in fragments whereas pronghorn sheaths are shed whole.

Fossil data from the proghorn date back to the Miocene. Antilocapra is the sole surviving member of a family that included at least thirteen genera in the Pliocene and Pleistocene.