Giraffes are one of the world's tallest mammals. They are well known for their long necks, long legs, and spotted patterns. Giraffes have small "horns" or knobs on top of their heads that grow to be about five inches long. These knobs are used to protect the head in fights. Giraffes are non-territorial, social animals. They travel in large herds that are not organized in any way. Herds may consist of any combination of sexes or ages.Female giraffes typically give birth to one calf after a fifteen-month gestation period. During the first week of its life, the mother carefully guards her calf. Young giraffes are very vulnerable and cannot defend themselves. While mothers feed, the young are kept in small nursery groups.