Giraffe , tallest of all animals. Giraffes inhabit dry, tree-scattered terrain south of the Sahara. The male averages 5.3 m (17 ft) in height, and with its 40-cm (15-in) tongue is able to reach high into acacia trees, the leaves of which are one of its main foods. The giraffe, like most mammals, has only seven neck vertebrae, which are greatly elongated to support its extremely long and muscular neck. Due to the great distance between the animal's heart and head, its vascular system is equipped with valves so that sufficient blood reaches the brain. Both sexes have two or four short, blunt, skin-covered horns. The long, flexible tongue and long, muscular upper lip are used to rip leaves from branches. Giraffes have chestnut brown blotches against a buff background, markings that blend with the dappled shadows of tree branches. As giraffes age, their color grows a darker brown. Each animal has a unique set of markings. A giraffe's life span is up to 26 years in the wild and up to 36 years in captivity. Giraffes have a keen sense of smell and hearing and an outstanding sense of sight. They congregate in loosely organized herds of two to ten members, with individuals often joining and leaving again. Each herd is led by an adult bull and consists of cows, calves, and sexually immature males. Giraffes gallop with the hind feet reaching in front of the fore feet and the neck swinging widely, giving the appearance of slow motion, although they can actually reach 56 km/h (35 mph). When walking they pace, moving the two feet of one side forward simultaneously. Due to their great weight, which averages 800 kg (1800 lb), they are unable to traverse boggy swamps or riverbeds. On dry, hard land, however, they range widely and are found hundreds of kilometers from water. Unlike many grass-eating herbivores of Africa, giraffes do not migrate during dry seasons because they get their food and most of their moisture from leaves. They can go for more than a month without drinking, and the few times they do drink, they must spread their long forelegs widely to reach the water. For this reason giraffes rarely graze grass. When giraffes vocalize, they emit moans or low notes. They usually sleep in standing positions. They protect themselves by kicking with their large, heavy hooves. Lions are their chief predators. During mating season males vie for females by butting with their heavy necks and heads. After about 15 months the cow bears a single calf, 1.7 to 2 m (5.6 to 6 ft) high, which can stand 20 minutes after birth. Calves come to sexual maturity in about four years. Once heavily hunted for their thick, leathery skins, giraffes are now protected .