Pronghorn (Antilocapra americana)
|Also known as:||Mexican pronghorn, Sonoran pronghorn|
|French:||Antilocapre, Antilope Américaine|
|Size||Shoulder height: 87 cm (2)|
Head-tail length: 141 cm (2)
|Weight||47 - 70 kg (2)|
Classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix I of CITES (2). Subspecies: Antilocapra americana mexicana, Antilocapra americana peninsularis and Antilocapra americana sonoriensis are listed on Appendix I of CITES (2).
Despite being similar in appearance and behaviour to antelopes, the pronghorn actually belongs to its own unique family (2) (4). The horns are particularly remarkable in that like bovids, they consist of a keratin sheath on a bony core, but like deer (cervids), they are forked, and the outer sheath sheds annually from the unforked bony core (2) (4) (5). Both sexes have black horns, but the male’s are enlarged and have forward-facing prongs below backward-pointing hooks, while the female’s are comparatively small (2) (4). The pronghorn’s stocky body is supported on long, slim legs, which enable it to take massive eight metre strides at full speed (2). The upperparts are largely red-brown to tan, while the underparts, the rump and two bands across the neck are contrastingly white. The male also has conspicuous black patches on the face and on the sides of the neck, beneath the ears (2) (4) (6). Five subspecies, which differ slightly in appearance, are commonly recognised, with larger, darker forms living in the north, and smaller, lighter forms in the south (1) (2).
Endemic to North America, the pronghorn’s range stretches from the southern Canadian Prairies through the western half of the United States to northern Mexico (1) (2) (5).
The pronghorn inhabits grasslands, brushlands and deserts, from sea level up to 3,350 metres (1) (2) (6).
Renowned for its speed, the pronghorn is the fastest terrestrial mammal in the Americas, capable of reaching top speeds of up to 86 kilometres per hour, and maintaining cruising speeds of 70 kilometres per hour for several kilometres at a time (2) (6). It is active both day and night, with slight peaks just before sunrise and after sunset (6). Many plants feature in the pronghorn’s diet, including a variety of forbs, shrubs, grasses and cacti (1) (2) (4) (6). Although it will drink freely if water is available, sufficient hydration can be derived from succulent plants if necessary (6). Daily movements vary depending on the seasons, with distances travelled during the winter typically being four times as far as during the summer (2).
During autumn and winter, the pronghorn often forms large, loose groups comprising as many as 1,000 individuals of all ages and both sexes (4) (6). However, in spring and summer, these large herds segregate into much smaller groups segregated by sex. In wetter areas, where food is abundant, the mature males are territorial and, beginning in early March, will compete amongst each other for territories. To define a territory, males will scent mark with urine, faeces and secretion from glands behind the ears. Usually fights between territorial males will be resolved with a staring match and possibly some angry vocalisations and chasing, but when all else fails, rivals will resort to head to head fighting. During this time, the female groups, which may contain as many as 23 members, move freely between the territories of different males, whilst being pursued by bachelor herds of young males that move about on the edges of the areas controlled by the territorial males. However, when it comes to mating, which takes place during a period of about three weeks between July and early October, it is only the dominant males defending the most food-rich territories that sire offspring. In less productive, arid areas, the males dispense with forming territories, but instead attempt to defend groups of females in order to mate (2) (6).
During the first pregnancy, females usually give birth to a single young after a gestation period of around 252 days, but subsequently, will often give birth to twins (2) (6). Young at just two days old can already run faster than a horse, but do not have the stamina to keep up with the herd. As a result, for the first three to four weeks, the young remain hidden in vegetation, where they are safer from predators such as coyotes and golden eagles. Females continue to nurse and groom the young for four to five months, with both sexes reaching maturity at around 16 months old. Given that only dominant male’s breed, most will have to wait until they are three to five years of age before siring their first offspring (2).
Prior to the arrival of European explorers, there were an estimated 35 million pronghorns roaming the plains of North America (1) (6). However, the subsequent wave of hunting and habitat loss that followed colonisation of the continent saw the pronghorn population crash to less than 20,000 by the early 1920s (1) (2) (6). Owing to substantial conservation efforts since then, numbers have fortunately recovered to an estimated 700,000 today (1) (6). While there are no longer any significant range-wide threats to the pronghorn, certain populations and subspecies are more vulnerable than others. In particular, there are estimated to be less than 300 Sonoran pronghorn (Antilocapra americana sonoriensis) remaining in the United States and only 200 to 500 in Mexico. The perilous decline of this subspecies is thought to be attributable to a range of factors, including fragmentation of habitat, fencing, livestock grazing and illegal hunting (1).
The pronghorn occurs in vast numbers in several large and well managed protected areas including the Yellowstone National Park. The Sonoran pronghorn is protected under the US Endangered Species Act (1), which requires the implementation of a recovery plan for listed species, as well as further scientific research, public education and the protection and restoration of critical habitat (7) (8). All the Mexican subspecies are also listed on Appendix I of CITES which prohibits international trade (1) (3).
To find out more about the US Endangered Species Act, visit:
The US Fish and Wildlife Service – Endangered Species Program:
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- Bovids: A member of the family Bovidae, which includes hooved, herbivorous ruminants such as cattle, sheep, goats, antelopes, gazelles and buffalo.
- Keratin: A group of fibrous proteins that form the basis of hair, nails, wool etc in animals.
- Subspecies: A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
IUCN Red List (August, 2009)
- Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
- Burnie, D. (2001) Animal. Dorling Kindersley, London.
Smithsonian National Museum of Natural History (September, 2009)
- Nowak, R.M. (1999) Walker's Mammals of the World. Johns Hopkins University Press, Baltimore, Maryland.
- Taylor, M.F.J., Suckling, K.F. and Rachlinski, J.J. (2005) The effectiveness of the endangered species act: a quantitative analysis. Bioscience, 55(4): 360 - 367.
- Clark, J.A., Hoekstra, J.M., Boersma, P.D. and Kareiva, P. (2002) Improving U.S. Endangered Species Act recovery plans: key findings and recommendations of the SCB Recovery Plan Project. Conservation Biology, 16: 1510 - 1519.
CITES (August, 2009)