It is common to see from one to seven males resident with a pride at any given time. If resident males are defeated by new males, they leave the pride and typically never return. Females have to defend their pride range against other females approximately every four days. Males probably have to defend less often against other males because nomadic males are relatively rare. In the Serengeti, the time of year makes a big difference.
Males probably encounter strange males more frequently in the wet season.
This is because nomadic males often follow the migrating wildebeest up north during the dry season and return to the Serengeti in the wet season. Surprisingly, there is still no sure answer to the question of why lions have manes. In the past people thought that the mane acted as protection in fights against other males. But lions often fight by biting each other on the back. Another possibility is that the mane acts as a signal to other lions.