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Diversity of Living Giraffidae (Giraffe and Okapi)
The family Giraffidae is one of a number of families in the mammal order Artiodactyla (even-toed ungulates). There are just two living species, the Giraffe (Giraffa camelopardalis) and the Okapi (Okapia johnstoni). Giraffes occur in a patchy distribution in savannas across parts of sub-Saharan Africa. Okapi are endemic to the forests of DR Congo.
Giraffes are the tallest mammals in the world. At birth, they stand between 1.5 and 1.8 m; at maturity, females may reach 4.5 to 5 m and males 5 to 6 m. Body mass at birth is around 100 kg (less in captive animals). Body mass of mature females can reach 1100 kg and mature males can reach 1500 kg. Giraffes have very long necks although, like nearly all other mammals, they have just seven cervical vertebrae—their cervical vertebrae are very long (as are their lower leg bones). The neck is held upright when a Giraffe walks, but stretched forward when it is running or moving uphill. A variety of morphological and physiological adaptations related to blood flow prevent problems from arising when the Giraffe lowers and raises its neck (e.g., to drink).
Okapi are secretive forest-dwellers that have been known to science only since 1901 (although they were already familiar to local indigenous people). They share some evident similarities with Giraffes, but bear an overall resemblance to some of the larger antelope species. In contrast to Giraffes, Okapi females are taller and more massive than males.
Ecology and Behavior
The structure of a Giraffe herd is fluid and the same individuals rarely stay together for long. Females and young are usually found in a herd together; younger males may form bachelor herds. Mature bulls are generally solitary, although they may join a temporary harem of females. Unlike Giraffes, which are not territorial, Okapi of both sexes hold territories.
The Giraffe is one of just two ungulate species known to have a gestation period longer than a year (450 days). In the wild, females become mature at 4 to 5 years. When her young is born (usually just one), a female may produce 10 liters of milk each day. Giraffe milk is richer in fat and protein than that of dairy cows. The gestation period for Okapi is shorter than that of Giraffes, around 14 months.
Giraffes are almost exclusively browsers. Acacia leaves are a major component of Giraffe diets, as are Combretum trees. Giraffes favor food plants rich in calcium and phosphorus, which are important in building their large skeletons. Giraffes use their powerful prehensile tongues to pull shoots and twigs into their mouths, where leaves are stripped off between the lower teeth and the upper dental pad. The tongue is very rough and Giraffes are reported to munch fully hardened thorns, although they prefer to feed on vegetation without thorns. Okapi feed on plants in their forest habitat. They use their prehensile tongues to strip leaves from branches and bring them into the mouth. An Okapi's tongue is so long it can wash its eyelids and ears with it.
Although Giraffes are generally able to survive on the water content of their food, when water is accessible they tend to come to drink at intervals of three days or less. Drinking Giraffes, with head lowered and forelegs splayed, are particularly vulnerable to predators.
Within historical times, Giraffes were widely distributed throughout Africa, but never in the tropical rainforest of the Congo River, which is home to the Okapi. The Giraffe's current distribution is far smaller than it once was and very patchy, but Giraffes can be found in a range of dry savanna habitats, from scrub to woodland, and are closely associated with acacia thornveld, as well as deciduous woodland tree species.
Male Giraffes often fight, striking one another with their necks and heads. These bouts are generally highly ritualized in young males, causing no injury, but when they occur between mature bulls they tend to be more serious. Although it has been suggested that the long necks of Giraffes are a product of sexual selection in males, with longer and heavier necks being favored in the struggle among males for mating opportunities, necks of both sexes grow in length and mass at similar rates.
Communication among Giraffes seems to involve mainly vision and olfaction.
Conservation Status of Giraffes and Okapi
Although the Giraffe is listed on the IUCN Red List as Least Concern, it has declined dramatically over parts of its range, especially in West Africa. It is now extinct in many countries where it once occurred, including Burkina Faso, Eritrea, Guinea, Malawi, Mauritania, and Senegal (and possibly Mali and Nigeria). Some named subspecies are in trouble as well. The Okapi is listed by IUCN as Near Threatened, although given its secretive nature, an accurate population assessment is difficult. Habitat loss is a serious threat. Okapi were once present in Uganda (and possibly elsewhere) but are no longer believed to occur anywhere outside DR Congo.