young bull who is seeking a mate from among his group, and expel him, but this is not a common practice. Herds change composition continually, so females are available for any young bull who comes along, and if they are willing, he can mate with them.
Giraffes are sexually mature at three to four years of age and reproduce sexually. Because of their individualistic nature and the fact that they do not form stable herds, giraffes are polygamous through their lifetime. Females usually mature earlier than males, and reach full height by five years. Females can calve from age five on, up until about 20 years of age. A sexually mature cow comes into heat every 12 to 15 days. Giraffes breed throughout the year, but mating tends to reach seasonal peaks in different regions of Africa. The gestation period for a giraffe is 15 months. Occasionally, twins are born, but more often just one calf. More than half the calves born die during the first year of life, usually as they fall prey to predators, such as lions (Lavine, p. 57).
Male giraffes are sexually mature at four and a half years, but do not reach their full height until seven years of age. Two unusual behavior patterns are associated with mating in giraffes: flehmening, and use of the
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