Chimpanzees (sometimes called chimps) are an exclusive African species of extant great ape. Native to sub-saharan Africa, chimpanzees are currently found in the Congo jungle. The male common chimp stands up to 3.9 ft high and weighs as much as 150 lb, the female is somewhat smaller. When extended, the common chimp’s long arms span one and a half times the body’s height. In trees, both species climb with their long, powerful arms, on the ground, chimpanzees usually knuckle-walk, or walk on all fours, clenching their fists and supporting themselves on the knuckles. Its coat is dark; its face, fingers, palms of the hands, and soles of the feet are hairless. The exposed skin of the face, hands, and feet varies from pink to very dark in both species, but is generally lighter in younger individuals and darkens with maturity. A bony shelf over the eyes gives the forehead a receding appearance, and the nose is flat. Although the jaws protrude, a chimp's lips are thrust out only when it pouts. Anatomical differences between the common chimpanzee and the bonobo are slight, but social behaviours are markedly different. Chimpanzees make tools and use them to acquire foods and for social displays; they have sophisticated hunting strategies requiring cooperation. Recent research indicates the chimpanzee stone tool use dates to at least 4,300 years ago. Chimpanzee tool usage includes digging into termite mounds with a large stick tool, and then using a small stick that has been altered to "fish" the termites out. There have been occasional unsubstantiated or controversial reports of Chimpanzees using rocks or sticks as weapons. A recent study claimed to reveal the use of spears, which common chimpanzees in Senegal sharpen with their teeth and use to stab and pry Senegal bushbabies out of small holes in trees. Chimpanzees are also known to use stones as anvils and hammers in order to break open nuts. Before the discovery of tool use in chimps, humans were believed to be the only species to make and use tools, but several other tool-using species are now known. The chimpanzee is an omnivore frugivore. It prefers fruit above all other food items and even seeks out and eats them when they are not abundant. It also eats leaves and leaf buds. Seeds, blossoms, stems, pith, bark and resin, insects, and meat make up the rest of its diet. While the common chimpanzee is mostly herbivorous, it does eat honey, soil, insects, birds and their eggs, and small to medium-sized mammals, including other primates. Nest-building, sometimes considered as tool use, is seen in chimpanzees which construct arboreal night nests by lacing together branches from one or more trees. It forms an important part of their behaviour, especially in the case of mothers who teach this trait to infants. Nests consist of a mattress, supported on a strong foundation, and lined above with soft leaves and twigs, and are built in trees with a minimum diameter of 16 ft and may be located at a height 10 to 150 ft.