Although not strictly nocturnal, hippopotamuses typically forage for food at night, and spend the day digesting their food, sleeping and socialising (2) (8). Diet mainly comprises grass, although isolated incidence of scavenging on carcasses has been observed (4) (9). On land, hippos disperse individually to forage, with the exception of mothers and dependent offspring (2). Water habitat is partitioned into individual mating territories by mature bulls (2). Herds within these territories typically number 10 to 15 individuals, but vary from 2 to 50 and can number in the hundreds at highest density when standing water availability declines. The groups are primarily made up of females and their young and are headed by a dominant male, although some subordinate, non-breeding males may also be tolerated in the group (2) (7). Adult males vie for control of these herds with intense aggression, using their long canine teeth in threat displays and as weapons (8). Losing males are forced to retreat and live in bachelor herds or alone in marginal habitat (2) (8). Although capable of breeding year-round, seasonal birth peaks coincide with peak rainfall (8). After a gestation of around 240 days, the cow gives birth to a single calf, generally underwater (4) (8). Young remain with their mother for many years, with cows being observed with up to four successive offspring. However, small calves are also often left in 'creches', which are guarded by one to several cows while the mothers forage (2). Males reach sexual maturity at between seven and nine years of age, whilst females attain maturity at eight to ten years (9).