At four days the young can outrun a human. At three weeks the fawn consumes some vegetation but still suckles on the solid-rich milk produced by the mother. Young are sexually mature at 15 to 16 months. Males generally do not mate until they are three years of age. Behavior Antilocapra americana can reach speeds of over 86 km per hour, making it the fastest New World mammal.
Pronghorn are both diurnal and nocturnal.
They show minor activity peaks just after sunset and before sunrise. Fall and winter foraging require that herds cover 3.2 to 9.7 km each day. Deep snows may cause herds to shift their ranges as much as 160 km. In the fall and winter pronghorn form large, loose herds of up to 1000 individuals of all age and sex classes. During the spring and summer the herd breaks up into smaller groups segregated by sex.