These gentle herbivores feed on plants growing within the water, and occasionally on the leaves of mangroves hanging over the water's edge (2), using their flexible flippers and bristly lips to push the vegetation into their mouths (6). African manatees consume such vast quantities of aquatic vegetation, maybe around 8,000 kilograms each year, that they have even been suggested as a natural method of aquatic weed control! (2). The large intestine of manatees is suitably enormous, sometimes up to 20 metres in length, in order to digest these great quantities (6). Even though the African manatee shares its habitat with sharks and crocodiles, humans are its only known predator (2). The social structure of the African manatee is little-known; it was once believed to be a monogamous animal, living in groups of an adult pair with their calves; however now it is thought more likely that the only strong bond is between a female and her calf (2). Like other manatees, the African species is believed to form large mating herds, consisting of a female in oestrus and several males, remaining together for up to a month. Within the month, the female is only receptive to mating for a day or two, during which time the males will shove and push each other in an effort to mate with the female, and the female will mate with several males (6). The African manatee gives birth to a single calf at a time, in a weedy swamp or shallow lagoon (2). The metre long newborn remains with its mother, swimming close by her side, for the first one to two years of its life (6).