The Impala ( Aepyceros melampus ) rams weigh around 55kg. Only the males have the beautiful lyre-shaped horns. The males are only territorial during the rut in autumn, during which they vigorously defend the territory against trespassers, by vocalising, chasing and other displays, such as snorting, strutting, head bobbing, horn clashing and head pushing. This may lead to short bouts of serious fighting during which it is not uncommon for one of the rams to lose a horn, followed by roaring which, to the uninitiated often sounds like a lion. Antelope do not regrow horns that have broken off.