Fertilization occurs by contact transfer without intromission, similar to some lizards. These structures make it harder for males to achieve intromission. The stimulation following intromission causes the female to be immobilized. The male pronghorn usually ejaculates immediately after intromission. Intromission only lasted a few seconds. Intromission lasts between 10 and 20 minutes. Also, they may evolve shield over their genital openings to prevent intromission. A pup may be mounted by its abductor, but intromission does not occur. In many species, for a LH surge to occur, little intromission is required. Intromission usually occurs in trees on horizontal limbs about off the ground.