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  The Mammals of Texas - Online Edition

Pronghorn
Order Artiodactyla : Family Antilocapridae : Antilocapra americana (Ord)

Pronghorn (Antilocapra americana).Description. A small, deerlike mammal with black, pronged horns that reach beyond the tip of the ears in males; in females they are shorter and seldom pronged; only two toes on each foot (no dewclaws); rump patch, sides, breast, belly, side of jaw, crown, and band across throat white; chin and markings on neck black or dark brown; black patch at angle of jaw in males (absent in females). Dental formula: I 0/3, C 0/1, Pm 3/3, M 3/3 X 2 = 32. External measurements of males average: total length, 1,470 mm; tail, 135 mm; hind foot, 425 mm; females, 1,250-135-400 mm. Weight of males, 40-60 kg; females somewhat smaller, averaging about 40 kg.

Species distribution mapDistribution in Texas. Formerly distributed over the western two-thirds of Texas, as far east as Robertson County in the north, and Kenedy County in South Texas. Now restricted to limited areas from the Panhandle to the Trans-Pecos.

Habits. The fleet-footed, large-eyed pronghorn is an animal of the plains. Adapted for speed and for seeing long distances, it inhabits areas where both its sight and its running will be unimpaired by woodland vegetation. Water in the immediate vicinity is not a requisite because the pronghorn is so adapted physiologically that it can go for long periods without drinking. Apparently, it has the ability to conserve body water and to produce metabolic water.

Among North American mammals, pronghorns are the most fleet-footed. The top speed at which they can run probably does not exceed 70 km an hour, and certainly it varies with individuals. An interesting trait of pronghorns is their highly developed sense of curiosity. They insist on examining at close range any unrecognized object, particularly one that is in motion. Because of this, it is possible for man to lure the animals within close range by hiding behind a bush and waving a handkerchief or other object slowly back and forth. Indians, and sometimes our present-day hunters, have utilized this ruse in bagging them. Another peculiar trait is their disinclination to jump over fences or other objects. A low brush fence no more than a meter high will ordinarily turn the animals, and it is not uncommon for small bands to be reduced almost to the point of starvation within a fenced enclosure while plenty of food is available on the outside. They can jump over moderately high obstructions, however, when hardpressed. Ordinarily, they crawl under or between the wires of barbed-wire fences.

The pattern of daily activities in Trans-Pecos Texas varies considerably with the season, daily weather, and interruptions from enemies or man’s activities. Usually, the animals rise shortly after daybreak and begin a period of intensive feeding lasting from 1 to 3 hours, followed by a period of lying down to rest. Resting for about 1 hour is followed by a long period of feeding through most of the morning. Near midday, another extended period of lying down occurs, succeeded by one or two feeding periods during the afternoon. When the heat of the day is intense in spring and summer, little activity takes place. After about 5 p.m., pronghorns feed steadily until nightfall, at which time they recline for a long period of rest. The alternation of feeding and resting is repeated at night, with longer periods of lying down than during the day.

Pronghorns feed entirely upon vegetation, chiefly shrubs and forbs. In Trans-Pecos Texas, Helmut Buechner found that their summer forage consists of about 62% forbs, 23% browse, and 15% grasses. All parts of the plants were consumed including leaves, stems, flowers, and fruits.

Pronghorns have a particular fondness for flowers and fruits. The flowers of cutleaf daisy, white daisy, stickleaf, paper flower, and woolly senecio are consumed in large amounts. Although paper flower is poisonous to sheep and woolly senecio is poisonous to cattle, pronghorns apparently suffer no ill effects from either and consume large quantities of both. They do suffer from locoweed (Astragalus mollissimus), although few eat enough of it to die from its poisonous effects.

Autumn forage consists of about 59% forbs, 34% browse, and 7% grasses. More browsing is done in fall than in summer. Winter forage is the same as that in late autumn, with some variation when snow covers the ground, during which time pronghorns consume larger quantities of green woolly senecio; the dried stems and old flower parts of broom weed, stickleaf, and groundswell; old heads of grama grasses; dried leaves of goatweed; and browse species such as javelina bush, Mexican tea, and sacahuiste. Little attempt is made to paw away the snow to get these plants. Cedar is used throughout the winter where available in large quantities. Four of the most important winter foods are cutleaf daisy, paper flower, fleabane, and wild buckwheat. In late February, early annuals become available. Early spring flowers, which appear about the middle of March, are eagerly sought. More grass is taken when new green growth appears in spring.

The breeding season of the pronghorn in Trans-Pecos Texas extends from the last week in August to the first week in October. The most vigorous bucks gather small harems of two to 14 does. Young bucks frequently linger at the outskirts of the harem herd and at times attempt to steal a doe or even to interfere with a mature buck in his mating activities. The master of the harem has an endless task in keeping his does together and warding off intruding bucks. The gestation period is between 7 and 7 months. The young (usually two) weigh from 2 to 4 kg each and appear in May or June. The female hides her young ones, and at first the fawns are active only a small part of the day. The female goes to them three or more times a day so they can nurse. When about a week old, they are able to walk and run well and begin nipping at vegetation. When a month old, they graze readily on green vegetation. When the fawns are a month to 6 weeks old, does and fawns gather together in small herds which are maintained well into and sometimes throughout the winter season. Nursing continues until the fawns are about 4 months old, so that most of them are weaned about the time of the onset of mating activities.

Sexual maturity is reached at the age of about 1 year in both sexes. There is some indication, however, that young does may breed late in the year in which they are born, as is the case in white-tailed deer. The covering of the horns is shed shortly after the breeding season, beginning about the middle of October and ending in early November. New horn growth is rapid but the prong is not evident until about the first week in December.

An apparently satisfactory method of judging the age of pronghorns is one also used for domestic sheep. Fawns are born with only two lower incisors and develop four teeth (three incisors and a canine) on each side of the lower jaw by fall. At the age of about 15 months, the first middle incisors are being replaced by permanent teeth; at 2 years the second incisors are replaced; at 3 years the third incisors are replaced; and at about 4 years the pronghorn has a full set of permanent front teeth. After 4 years, age must be judged on the spread of the two middle incisors and the amount of wear on all of the teeth. The life-span under natural conditions may be as much as 12-14 years, but the average age attained is probably considerably less.

The pronghorn is one of our more desirable game species, but despite extensive management efforts it has been decreasing in numbers in recent years. The estimated statewide population in 1990 was 13,920 and the 1989 harvest by hunters was 543.

It is commonly believed that these animals compete seriously with livestock for available forage on the range. According to Buechner, the total amount of competition between cattle and pronghorns is approximately 25%. Competition with sheep is much more severe, reaching at least 40%, as determined by studies in Trans-Pecos Texas. Pronghorns are far more dependent upon weeds than are sheep, and where sheep have eliminated these plants on heavily stocked ranges pronghorns cannot successfully maintain themselves.