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Pronghorn, Antilocapra americana

The pronghorn (Antilocapra americana) is native to the central areas of North America, where it is also known as the prong buck, or pronghorn antelope and antelope, although it only resembles true antelopes. The pronghorn is the only remaining species in the Antilocapridae family, which once held five other species. Its range stretches throughout the United States, and starts in Alberta and southern Saskatchewan in Canada. It holds five subspecies, including the Baja California Pronghorn, which is endangered.

The pronghorn was first described by Lewis and Clark, when they traveled through what is now the state of South Dakota. It is most often found in grasslands, but will reside in deserts or brush lands. One continuing study, conducted by the Wildlife Conservation Society and the Lava Lake Institute for Science and Conservation, shows that the pronghorn can migrate over 160 miles throughout these habitats, beginning the journey in the Pioneer Mountains, moving through Craters of the Moon National Monument, and ending at the Continental Divide.

The pronghorn can reach an average height of up to 41 inches at the shoulder, but males and female vary in body length and weight. Males can weigh between 79 and 150 pounds, with an average length of almost five feet, while females weigh up to 110 pounds. Both males and females bare only two hooves on each foot, and have an average body temperature of 100 degrees Fahrenheit.

The horns of the pronghorn are similar to horns of other species, but also show structural differences. Like the horns of species within the Giraffidae family, the pronghorn has skin covering the bony cores of each horn. However, the horns also develop a casing of keratin surrounding them, and this covering is shed every year. Although members of the Bovidae family also develop sheathes, these are not the same as the pronghorn’s forward angled horns.

These horns are more developed in males than in females, reaching a length of up to 9.8 inches, although they can reach 17 inches. Females’ horns are typically much smaller, reaching an average length of only 4.7 inches and do not usually curve to form a prong. Males bare a distinct patch of darker fur on the slant of the jaw, distinguishing them from females. Both sexes have tawny to reddish fur and a white underbelly.

The pronghorn is able to sustain high speeds for long periods, although the speeds vary between individuals. It is thought that this species is the second fastest land mammal on Earth, and the quickest in North America. It is thought that the pronghorn reaches such speeds in order to outrun predators, and this would have been important to populations co-existing with the extinct American cheetah.

This species is built for running, with a large heart and sturdy body, but it is not adept in jumping. Sheepherders throughout its range often erect fences with barbed wire, but because the pronghorn travel under these fences, groups like the Arizona Antelope Foundation are building safer fences, or removing the wire from current fences. The pronghorn is able to move about with 13 different gaits. Its common predators include the bobcat, wolf, and coyote.

The pronghorn will gather in herds that contain both males and females during the winter. These groups split when spring begins, with young males forming bachelor groups and females forming their own groups. Older males will live alone until winter returns. Both male and female groups will encounter groups of the same sex and may form larger groups when this occurs in the summer and fall. Within female herds, there is a prominent dominance hierarchy. Females may form a few close relationships, but the dominant females will not hesitate to chase off strange females when feeding.

Male pronghorns often mark a territory using a scent glands found on the sides of the head. However, this most often occurs when rain is abundant. In more arid conditions, males most often do not hold a territory, instead choosing to travel with a female harem group. When a male holds a territory, he may defend it by using vocalizations or by chasing other males off.

Females who are not currently within a harem group will “sample” male territories, moving between the areas during her estrous cycle. Outgoing females that do not switch territories will instigate a fight between males, and the females within her group will watch, and then choose to mate with the victor. Some females within a non-harem group that are not as outgoing will choose a male and remain with him in his territory.

When courting begins, a male will approach a female, waving his head from side to side and emitting soft vocalizations. If the female accepts the male, she will sniff his scent glands and permit him to mount her. After this occurs, in the middle of September, the female becomes pregnant for up to 235 days. Most births occur in late May, consisting of one fawn that weighs between 4.4 and 8.8 pounds. For up to the first 26 days of its life, the fawn will hide in thick vegetation, spending between 20-25 minutes a day with its mother and this continues even when the fawn joins a nursery.

Mothers take the responsibility of caring for the fawns, including protecting them from danger. Weaning occurs at different times for male and female fawns, with males being weaned two or three weeks before females. Although males reach sexual maturity at up to 16 months, most will not breed until three years of age. The typical lifespan of this species is ten years, with some individuals reaching 15 years of age.

The diet of the pronghorn consists of many types of vegetation, especially the types that domestic livestock do not prefer. However, these species do compete for certain types of food. Plant materials consumed include forbs, shrubs, grasses, and cacti.

In the 1920’s, the population of pronghorns was approximately 13,000 due to over hunting. However, these numbers have grown to between 500,000 to 1,000,000 because of hunting limitations and habitat conservation and protection. The blue tongue disease, which is transferred by sheep, has compromised a few local populations but it has not caused local extinction thanks to conservation efforts. Migration paths have been compromised by habitat fragmentation, and in one area, there is only a path that is 600 feet wide for the pronghorn to pass through.

At one point, the pronghorn outnumbered people in its northern Colorado and Wyoming ranges, but only until hunting of the species was legalized. With no major threats to the species as a whole, the pronghorn is hunted in western areas of its range for food and for population control. The Sonoran pronghorn, however, is declining in number because of illegal hunting and habitat destruction, but it is protected by law under the US Endangered Species Act. There are two other subspecies of pronghorn that are considered endangered. The pronghorn appears on the IUCN Red List with a conservation status of “Least Concern”.

Image Caption: Pair of pronghorn (Antilocapra americana). Credit: photogramma1/Wikipedia  (CC BY-SA 2.0)

Pronghorn Antilocapra americana


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