Also called the lesser apes or small apes, gibbons differ from great apes (chimpanzees, bonobos, gorillas, orangutans and humans) in being smaller, exhibiting low sexual dimorphism, and not making nests. Like all apes, gibbons are tailless. Unlike most of the great apes, gibbons frequently form long-term pair bonds. Their primary mode of locomotion, brachiation, involves swinging from branch to branch for distances up to , at speeds as high as . They can also make leaps up to , and walk bipedally with their arms raised for balance. They are the fastest and most agile of all tree-dwelling, nonflying mammals.