Other palaeosubspecies are known, including those belonging to C. elaphus rianensis from the Middle Pleistocene of Italy, C. elaphus siciliae from the late Middle and Late Pleistocene of Sicily. Behaviour Mature red deer (C. elaphus) usually stay in single-sex groups for most of the year. During the mating season, called the rut, mature stags compete for the attentions of the hinds and will then try to defend the hinds they attract. Rival stags challenge opponents by belling and walking in parallel. This allows combatants to assess each other's antlers, body size and fighting prowess. If neither stag backs down, a clash of antlers can occur, and stags sometimes sustain serious injuries. Red deer are among the mammals exhibiting homosexual behavior. Dominant stags follow groups of hinds during the rut, from August into early winter. The stags may have as many as 20 hinds to keep from other, less attractive males. Only mature stags hold harems (groups of hinds), and breeding success peaks at about eight years of age. Stags two to four years old rarely hold harems and spend most of the rut on the periphery of larger harems, as do stags over 11 years old. Young and old stags that do acquire a harem hold it later in the breeding season than those stags in their prime. Harem-holding stags rarely feed and lose up to 20% of their body weight. Stags that enter the rut in poor condition are less likely to make it through to the peak conception period. Male European red deer have a distinctive roar during the rut, which is an adaptation to forested environments, in contrast to male American elk stags which "bugle" during the rut in adaptation to open environments. The male deer roars to keep his harem of females together. The females are initially attracted to those males that both roar most often and have the loudest roar call. Males also use the roar call when competing with other males for females during the rut, and along with other forms of posturing and antler fights, is a method used by the males to establish dominance. Roaring is most common during the early dawn and late evening, which is also when the crepuscular deer are most active in general. Breeding, gestation and lifespan Female red deer reach sexual maturity at 2 years of age. Red deer mating patterns usually involve a dozen or more