Figure 1.The pronghorn antelope (Antilocapra americana) is the rarest and least-known hoofed-mammal classified as a game species in the state of Washington.
The pronghorn antelope (Antilocapra americana) is the rarest and least-known hoofed-mammal classified as a game species in the state of Washington. (Woodland caribou, Rangifer tarandus caribou, are rarer, but are classified as Endangered under both Federal and Washington’s state endangered species statute). Although often called simply “antelope”, pronghorns are not true antelope at all; most authorities consider them the sole modern member of the family Antilocapridae, whereas all other horned-ungulates (mammals with hooves) in North America belong to the family Bovidae.
Pronghorns are rather small ungulates, measuring from 1 to 1.5m (3 to 5 ft) from head to tail, and from 0.8 to 1.0m (2.5 to 3 ft) at shoulder height. Adults weigh from 35 to 70 kg (77 to 154 lbs). As their name implies, males (and occasionally females) carry black horns that consist of a sheath made of keratin overlaid atop a permanent, boney core. Female horns, if present, are little more than protuberances, but those of males have a distinctive shape, with a sharp, backwardly tip and a forward-point “prong”. The horn sheaths of males are shed after rut, and re-grown each year. Both males and females feature a cinnamon-brown coat on their back, with white- under-side pelage, as well as 3-4 white-colored bands on the under surface of the neck.
Supremely adapted to open, relatively flat grasslands and shrublands, pronghorns are great travelers, and some populations migrate large distances annually. They are generally considered the fastest land mammals in North America, sometimes referred to as “speed-goats”. Pronghorns typically live in groups (larger in winter than summer), although breeding males will separate themselves into small territories in autumn to which they attempt to entice adult females.
Pronghorn females typically give birth – often to twins – on about their 2nd birthday. When on a high nutritional level, pronghorn populations can thus increase rapidly. Pronghorn fawns, however, are susceptible to coyote predation, starvation, and other sources of mortality. Pronghorns do not tolerate deep snows well, and thus populations can decline severely during harsh winters, particularly if they are unable to migrate to areas with less snow. Although their anatomy enables them to sprint with ease, they are poor leapers, and do not easily jump over fences the way deer and elk do. Instead, pronghorn typically crawl under fences when wishing to cross, but poorly constructed fences can impede normal migratory movements and cause mortality.
Washington represents the northwestern extent of historically occupied pronghorn range. Pronghorns declined greatly throughout their range in the 19th century, at which time they were extirpated from Washington. This may be the reason some books and references continue to show their native range as excluding Washington. That said, pronghorns were probably never numerous in the state; rather, their populations ebbed and flowed with large-scale climate changes and migrations. Historical records are clear, however, that pronghorns did at least occasionally occupy much of the central portion of the state, between the Cascades and the forested northeast and Blue Mountains.
The Washington State Game Department (the predecessor agency to the current WDFW) attempted to establish pronghorn populations by reintroduction on three separate occasions, none of which could be termed successful. In the late 1930s, pronghorns from Nevada were introduced to what is now the Yakima Training Center, after first being kept in captivity. In 1950, a separate attempt was made to introduce pronghorns in Adams County, near Ritzville. In 1968, a small number of pronghorns were released in Kittitas and Grant Counties. Although many animals survived, reproduced, and moved widely, no animals were known to have survived past the mid-1980s.
In January 2011, the Yakama Nation reintroduced 99 pronghorns from Nevada onto the Yakama Reservation, with financial and technical assistance provided by Shikar SCI and Safari Club International Chapters in Washington State. Nineteen of these wore VHF radio-collars (all of which had ceased operating by autumn 2014). Reproduction has been documented, although the exact number and distribution of these pronghorns is not known. Some of these animals have evidently moved off the Reservation, particularly to the south and east. WDFW occasionally receives reports of small groups or individual pronghorn, east as far as Pasco and south as far as the Columbia River. Separately, a group of three bucks and a doe were observed in Asotin and Garfield Counties in 2013. Their origin in not known with certainty, but biologists suspect they originated from adjacent Oregon. As of autumn 2014, the doe had evidently died or dispersed, and the three bucks were last seen headed south back into Oregon. The Confederated Colville Tribes have expressed interest in reintroducing pronghorns to the Colville Reservation, and begun planning efforts. With outside funding, WDFW completed an assessment of habitat suitability for pronghorn in a number of eastern Washington locations in 2006. However, to date, no comprehensive plans exist for reintroducing pronghorns outside of tribal lands.
Pronghorns in Washington are classified as a game species. There are currently no hunting seasons authorized by the Washington Fish and Wildlife Commission, and thus all pronghorns outside tribal lands are legally protected.
See: Summary report: Pronghorn antelope abundance survey in south-central Washington February 25-26, 2015
Pronghorns are occasionally observed on private lands within Washington. It is useful, therefore, to understand some of the important aspects of their biology that are relevant to coexistence.
Food habits. With their small mouth and specialist teeth, pronghorns are selective feeders. Diets vary depending on geography and availability, so it is difficult to characterize a universally preferred forage. In general, however, pronghorns have been found to prefer forbs over grasses and shrubs over herbaceous material. Pronghorns are known to eat cactus, and many populations subsist largely on sagebrush. However, when available, pronghorns will enter fields of alfalfa, winter wheat, and other cereal crops, causing local damage. At least one study in Kansas, however, suggested that even when present in fields, pronghorns may not forage on winter wheat. Damage is more likely to alfalfa and hayfields. Because of their preference for open spaces where they can detect and escape from predators, they are unlikely to enter orchards, vineyards, or areas with tall crops (e.g., corn, sunflowers). Similarly, they generally avoid both riparian zones and forested areas.
Diseases.All wild animals must cope with naturally occurring pathogens and parasites. Die-offs of pronghorn attributed to the blue-tongue virus have occurred. They are also susceptible to the closely-related epizootic hemorrhagic disease virus. Such disease outbreaks were likely related to exposure of pronghorns to livestock (transmission has apparently not occurred from wild pronghorns to livestock). Individual pronghorns have been documented as succumbing to pneumonia, rabies, and caseous lymphadenitis. Importantly, because pronghorns often live near domestic livestock, they have not been documented as susceptible to (or carriers of) brucellosis, bovine tuberculosis, bovine anaplasmosis, or leptospirosis.
Avoiding or minimizing conflicts:Because of their small size, their ‘dainty’ dietary habitats, and their frequent movements, pronghorns are rarely considered a major agricultural pest. However, in specific circumstances and in local areas, pronghorns can cause damage, particularly to alfalfa fields and stockpiled hay. According to Schemnitz (1994), a number of preventative measures can be taken to reduce pronghorn damage to agricultural crops. These include:
- Installing woven wire fences of 8-inch mesh, 48 inches high near agricultural fields;
- Installing electric fences with two wires spaced at 8 to 10 inches and 3 feet above the ground;
- Installing a single strand of electric wire painted with molasses as an attractant and 30 to 36 inches above the ground;
- Planting tall crops, such as corn, as a barrier between rangelands and small grain fields;
- In cases of temporary damage, using propane or acetylene exploders to repel or deter pronghorns.
Suggested reference:Schemnitz, S. 1994. Pronghorn antelope. In Prevention and Control of Wildlife Damage — 1994. Cooperative Extension Division, Institute of Agriculture and Natural Resources, University of Nebraska – Lincoln.