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Pronghorn Antelope (Antilocapra americana)



Pronghorn Antelope (Antilocapra americana)
Order: Artiodactyla, Family: Antilocapridae

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



I. GEOGRAPHIC RANGE
  • Occurs from southern Alberta and southern Saskatchewan, Canada through the western United States to Hidalgo, Baja California, and western Sonora, Mexico.
II. PHYSICAL CHARACTERISTICS
  • Mass: 36 to 70 kg.
  • The pronghorn antelope's horns are indeed pronged and consist of a permanent bony core covered by a keratinous sheath, shed annually. Males' horns extend past the tips of their ears. Females often bear horns, which are rarely pronged and no longer than their ears. Males' horns average 250 mm while those of females average 120 mm.
  • They have a long, woolly undercoat covered with coarse, brittle hairs. They are 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; females lack these black markings.
  • Head and body length ranges from 1000 to1500 mm, tail length from 75 to 178 mm, and shoulder height from 810 to 1040 mm. Males are, on average, 10 percent larger than females.
  • Females usually have four mammae, but six have been recorded in some individuals.
III. FOOD HABITS
  • As the pronghorn is fairly widely distributed over several habitat types, its diet depends on local resources.
  • Browse makes up approximately 80 percent 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 pronghorns 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 pronghorns eat more forbs and less browse than northern pronghorns. A study of Kansas pronghorns estimated that cactus makes up 40 percent of their diet, grass 22 percent, forbs 20 percent and browse 18 percent.
  • The pronghorn does not drink free water unless the forbs and other vegetation it consumes are low in water.
  • Pronghorns will dig through snow with their forefeet to obtain vegetation in the winter.
IV. REPRODUCTION
  • Pronghorn are polygamous, meaning that individuals mate with multiple partners.
  • In the northern part of their range, breeding occurs during a three-week period between mid-September and early October. In the southern part of their range, breeding begins earlier in the year, like late July.
  • Gestation lasts 252 days. Usually, females give birth to one young after their first pregnancy and to two young in subsequent pregnancies.
  • The weight of the newborn fawn ranges from 2 to 4 kg. The young have a gray pelage unlike that of the adults until they are three months old.
  • At four days the young can outrun a human. At three weeks the fawn consumes some vegetation but still suckles on the solid-rich milk produced by the mother. Young are sexually mature at 15 to 16 months.
V. BEHAVIOR
  • The pronghorn 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 pronghorns form large, loose herds of up to 1,000 individuals of all ages and sex classes. During the spring and summer the herd breaks up into smaller groups segregated by sex. At this point males over three years 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 males 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 competition for the best food sources between females and bachelor males.
  • After the mating season, horn sheaths are shed and hierarchical distinctions become unclear.
  • 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.
VI. HABITAT
  • The pronghorn is found from sea level to 3,353 meters in grassland and desert.
  • A 1964 study estimated the percentage of the entire species found on various vegetative communities and found that 62 percent lived on grasslands, 37 percent on grassland-brush land (mostly bunchgrass and sagebrush) and 1 percent on desert.
VII. ECONOMIC IMPORTANCE FOR HUMANS
  • Positive
    The pronghorn is the second most popular game animal in North America. 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.
      VIII. CONSERVATION
      • 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.
      IX. OTHER COMMENTS
      • Populations of pronghorn have been mixed through transplantation. More than 4,000 animals were transplanted in New Mexico between 1936 and 1957. Also, grassland herds in southern Arizona received transplants 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 pronghorn 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.



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