The Pronghorn is the fastest North American land animal, capable of sustained speeds of 40-50 mph and sprints up to 60mph. Speed is its main defense and no predator can catch a healthy adult pronghorn on the run. They are most at risk from predation as newborns when their mother hides them in the tall vegetation and guards them closely. Even so it is estimated some 30-40% of newborns fall victim to predators. At about three weeks of age the youngsters come out of hiding and begin foraging with several females, their offspring, and yearling females in nursery herds.
Often mistakenly called antelope, they are not of that family which is native to Africa and Asia. It is probably a tag that dates from observations noted during the Lewis and Clark expeditions. Once close to 40 million roamed North America, but the settlement of the west decreased their numbers to about 20k at the turn of the century. About 5000 reside in the Yellowstone area today.