Lions are unique among cats in that they live in a group, or pride. The members of a pride typically spend the day in several scattered groups that may unite to hunt or share a meal. A pride consists of several generations of lionesses, some of which are related, a smaller number of breeding males, and their cubs. The group may consist of as few as 4 or as many as 37 members, but about 15 is the average size. Each pride has a well-defined territory consisting of a core area that is strictly defended against intruding lions and a fringe area where some overlap is tolerated. Where prey is abundant, a territory area may be as small as 20 square km (8 square miles), but if game is sparse, it may cover up to 400 square km. Some prides have been known to use the same territory for decades, passing the area on between females. Lions proclaim their territory by roaring and by scent marking. Their distinctive roar is generally delivered in the evening before a night's hunting and again before getting up at dawn. Males also proclaim their presence by urinating on bushes, trees, or simply on the ground, leaving a pungent scent behind. Defecation and rubbing against bushes leave different scent markings. There are a number of competing evolutionary explanations for why lions form groups. Large body size and high density of their main prey probably make group life more efficient for females in terms of energy expenditure. Groups of females, for example, hunt more effectively and are better able to defend cubs against infanticidal males and their hunting territory against other females. The relative importance of these factors is debated, and it is not clear which was responsible for the establishment of group life and which are secondary benefits.
