At Home in Nature

  (Agate, Colorado)
TwoInTents Blog

Posts tagged [pronghorn]

Antelope seen! (Or were they?)

Another exciting day today in Elbert County!  I saw pronghorn today ambling across an open field.  Pronhorn have been clocked traveling as fast as 86 miles per hour, and are the fastest animals in North America (who don’t drive cars) but today, while pausing to sample the local salad bar, they seemed dissatisfied with the greens and continued on their way at  slow walk.

Though not an antelope, it is often known colloquially in North America as the Prong Buck, Pronghorn Antelope, or simply Antelope, as it closely resembles the true antelopes of the Old World and fills a similar ecological niche due to convergent evolution.  It is the only surviving member of the family Antilocapridae: during the Pleistocene period, 12 antilocaprid species existed in North America.  About 5 existed when humans entered North America about 13,000 years ago; all but A. americana are now extinct.  University of Idaho zoologist John Byers has suggested that the Pronghorn evolved its running ability to escape from extinct predators such as the American cheetah, since its speed greatly exceeds that of extant North American predators.

Each horn of the Pronghorn is composed of a slender, laterally flattened blade of bone that grows from the frontal bones of the skull, forming a permanent core. As in the Giraffidae, skin covers the bony cores, but in the Pronghorn it develops into a keratinous sheath which is shed and regrown on an annual basis. Unlike the horns of the family Bovidae, the horn sheaths of the Pronghorn are branched, each sheath possessing a forward-pointing tine (hence the name Pronghorn). The horns of males are well developed.

Males have a prominent pair of horns on the top of the head, which are made up of an outer sheath of hairlike substance that grows around a bony core; the outer sheath is shed annually. Males have a horn sheath about 12.5–43 cm (mean 25 cm) long with a prong. Females have smaller horns, ranging from 2.5–15 cm (average 12 cm), and sometimes barely visible; they are straight and very rarely pronged.

Males are further differentiated from females in that males will have a small patch of black hair at the angle of the mandible. Pronghorns have a distinct, musky odor. Males mark territory with a scent gland located on the sides of the head. They also have very large eyes, with a 320 degree field of vision. Unlike deer, Pronghorns possess a gallbladder

Pronghorns were brought to scientific notice by the Lewis and Clark Expedition, which found them in what is now South Dakota, USA. The range extends from southern Saskatchewan and Alberta in Canada south through the United States (southwestern Minnesota and central Texas west to coastal southern California and northern Baja California Sur, to Sonora and San Luis Potosí in northern Mexico.

Pronghorns form mixed-sex herds in the winter. In early spring the herds break up with young males forming bachelor groups, females forming their groups and adult males living a solitary life.  There are female bands which share the same summer range and bachelor male bands form between spring and fall. Females form dominance hierarchies with few circular relationships.  Dominant females will aggressively displace other females from feeding sights.

Adult male pronghorns employ two different mating strategies during the breeding season. A pronghorn male will defend a fixed territory that females may enter or it might defend a harem of females. A pronghorn may change mating strategies depending on environmental or demographic conditions. In areas that have high precipitation, adult male pronghorn tend to be territorial and maintain their territories with scent marking, vocalizing and challenging intruders.  In these systems, territorial males have access to better resources than bachelor males. [20] Females also employ different mating strategies. “Sampling” females visit several males, remain with each male a short time, and switch between males at an increased rate as estrus approaches. “Inciting” females behave as samplers until estrus; then they move away from the male, inciting fights and other aggressive competition. Inciting females watch the competition, and they always mate immediately with the winning male. “Quiet” females move to an isolated, peripheral location occupied by a single male, and remain with that male throughout estrus. 

All three female mating behaviors have advantages for the herd, and have helped to make the Pronhorn a strong survivor of the post-ice age thaw.

Pronghorns have a gestation period of 235 days, longer than is typical for North American ungulates. They breed in mid-September, and the doe carries her fawn until late May. This is around six weeks longer than the white-tailed deer. Newborn Pronghorns weigh 2--4 kg, most commonly 3 kg. In their first 21-26 days, a fawn spends time hiding in vegetation.  Fawns interact with their mothers for only 20-25 minutes a day and this continues even when the fawn joins a nursery. The females nurse, groom, distract predators and lead their young to food and water.  Males are weaned 2-3 weeks earlier than females.  Sexual maturity is reached at 15 to 16 months, though males rarely breed until 3 years old. The longevity is typically up to 10 years, rarely 15 years.

Pronghorn were nearly destroyed by humans, who also were partially responsible for the destruction of many other ice-age creatures.  By the 1920s, hunting pressure had reduced the Pronghorn population to about 13,000.  Protection of habitat and hunting restrictions have allowed their numbers to recover to an estimated population of between 500,000 and 1,000,000. There has been some recent decline in a few localized populations, due to blue tongue disease which is spread from sheep; however the overall trend has been positive since conservation measures were put in place.

Pronghorn migration corridors are threatened by habitat fragmentation and the blocking of traditional migration routes. In a migration study conducted by Lava Lake Institute for Science and Conservation and the Wildlife Conservation Society, at one point the migration corridor bottlenecks to an area only 200 yards wide.

Pronghorns are now quite numerous and outnumbered people in Wyoming and parts of northern Colorado until just recently. It is legally hunted in western states for purposes of population control and food, the meat is rich and lean. There are no major range-wide threats, although localized declines are taking place, particularly to the Sonoran Pronghorn, mainly as a result of, among others, livestock grazing, the construction of roads, fences and other barriers that pose barriers to historical habitat, illegal hunting, insufficient forage and water, and lack of recruitment.

Three subspecies are considered endangered in all (A. a. sonoriensis, A. a. peninsularis), or part of their ranges (A. a. mexicana). Populations of the Sonoran Pronghorn in Arizona and Mexico are protected under the US End

angered Species Act (since 1967), and a recovery plan for this subspecies has been prepared by USFWS (U.S. Fish and Wildlife Service 1998).  Mexican animals are listed on CITES Appendix I. Pronghorns have game-animal status in all of the western states of the United States, and permits are required to trap or shoot pronghorns

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