Okapis and giraffes

(Giraffidae)

Class Mammalia

Order Artiodactyla

Suborder Ruminantia

Family Giraffidae

Thumbnail description
Large to very large ruminants with high shoulders, sloping backs, long legs and neck, and two skin-covered horns. Very long, black, prehensile tongue; disruptive patterned coats for camouflage

Size
5–11 ft (1.5–3.3 m) shoulder height; up to 18 ft (5.5 m) to top of head; 460–4,250 lb (210–1,930 kg)

Number of genera, species
2 genera; 2 species

Habitat
Savanna and forest

Conservation status
Lower Risk/Conservation Dependent: 1 species; Lower Risk/Near Threatened: 1 species

Distribution
Sub-Saharan Africa

Evolution and systematics

Giraffes evolved relatively late, probably about 25 million years ago in the lower Miocene, from a branch of the even-toed ungulates, which was also to produce cattle, antelopes (Bovidae), and deer (Cervidae). Giraffids of various forms roamed Europe and Asia, benefiting from the climate change that saw subtropical woodland replaced by open savanna grasslands. This habitat change also allowed ruminants to spread and diversify into Africa. The most primitive form that can be distinctly classified as giraffes was Paleotraginae, which had a short neck and was about the size of red deer. They are generally considered the immediate ancestor of the modern giraffe. The okapi is very similar to this ancestral form of giraffe.

Physical characteristics

The most familiar of the two Giraffidae species, the giraffe (Giraffa camelopardalis), is the world's tallest mammal and largest ruminant. Males stand up to 11 ft (3.3 m) at the shoulder, but a very long neck of up to 8 ft (2.4 m) means the height of the top of their horns may be 18 ft (5.5 m) from the ground. The neck has only seven vertebrae, like most other mammals, but these are greatly elongated and strung with tendons and muscles anchored to a shoulder hump. A male giraffe weighs up to 4,350 lb (1,930 kg). Females are about 2–3 ft (0.7–1 m) shorter, and weigh up to 2,600 lb (1,180 kg). The giraffe's body is comparatively short, with high shoulders sloping steeply to the hindquarters. Legs are long, and the dinner-plate sized hooves are cloven. The giraffe's tail is hock length (up to 39 in [1 m]), with a long tassle.

The giraffe's head tapers to a point, eyes are large, and the tongue is black and very long (18 in [45 cm]). Both male and female giraffes have horns of solid bone covered with skin and up to 5 in (13.5 cm) long. Females' horns are thin and tufted, while males have thicker horns but the hair is worn smooth by sparring. Males also have a median horn and four or more smaller bumps. Giraffes are one of the few animals born with horns.

The giraffe's forest cousin, the okapi (Okapia johnstoni), has a number of features in common, including two skin-covered horns up to 6 in (15 cm) long (absent in females), a long,

prehensile, black tongue, and lobed canine teeth. But while its neck is long relative to most ruminants, it is not nearly so well developed as the giraffe's. Superficially, the okapi more closely resembles a horse. Its shoulder height is no more than 5.6 ft (170 cm) and its weight no more than 550 lb (250 kg). The okapi's body also slopes to its hindquarters, but its head is more horse-like, with large, flexible ears.

Both giraffe and okapi have patterned coats that help camouflage them in their respective habitats. The giraffe's coat varies from pale brown to rich chestnut, dissected by a tapestry of creamy buff lighter hair. Patterns not only vary among subspecies, but each individual giraffe has a unique pattern. The giraffe's scientific name, camelopardalis, means "camel marked like a leopard." The okapi's coat is dark, chestnut to chocolate brown in color, with distinctive creamy white stripes on the upper legs, white stockings on the ankles, and dark garters at the leg joints. The head is lighter colored than the body, with a black muzzle.

The giraffe's unique evolutionary design has required adaptations of its circulatory and respiratory systems. Unusually elastic blood vessels and a series of valves help offset any sudden buildup of blood when the head is raised, lowered, or swung rapidly, keeping the animal from blacking out. Arteries near the feet are thick-walled and less elastic, with thick, tight skin around the lower leg, decreasing downward blood pressure and helping to avoid edema.

The giraffe's heart is enormous, 2 ft (60 cm) long and weighing 25 lb (11 kg). Beating up to 170 times a minute, it pumps the highest known blood pressure of any mammal, more than twice that of humans. Yet blood pressure in the giraffe's brain is similar to most other large mammals. Giraffes also breathe rapidly, around 20 times a minute, as the long neck contains partially inhaled and exhaled air that must be cleared.

Distribution

Both Giraffidae species are confined to sub-Saharan Africa. In historic times, the giraffe was found throughout arid and dry savanna zones, wherever trees occurred. That range has now been halved, and the giraffe has disappeared from most of West Africa (apart from a residual population in Niger). Elsewhere it remains fairly common, and is not confined to reserves. Okapis have a much more restricted range in rain-forest in the Democratic Republic of the Congo (Zaire).

Habitat

Giraffes inhabit arid and dry savanna zones where there are adequate feed trees. Okapis, thought of as forest giraffes, require a quite different habitat of dense, moist, tropical lowland forest. They prefer secondary forest, near water, and are usually found at altitudes of 1,600–3,200 ft (500–1,000 m).

Behavior

Giraffes and okapis exhibit very different forms of social behavior. Giraffes are sociable, living in loose, open, unstable herds of up to 20 animals, with individuals joining and leaving the herd at will. Herds can be all female, all male, females with young, or of mixed genders and age. But in general, females are more sociable than males. A female giraffe is only likely to be out of sight of another female when calving, whereas mature males wander more widely in search of estrous females. Giraffes are non-territorial, but do have home ranges that can vary enormously in size, from 2 to 252 mi² (5–654 km²), depending on food and water availability. Giraffes have been known to cover 580 mi² (1,500 km²) in the Sahel of Niger looking for food in the dry season.

Okapis live mainly solitary lives, or in mother-offspring pairs, although ephemeral groupings are occasionally seen feeding together at prime food sites. Okapis have individual, overlapping home ranges of about 1–2 mi² (2.5–5 km²), with estimated population densities of 0.25–1 animals per mi² (0.1–0.4 km²).

Both species appear to have a dominance hierarchy among males. Sub-adult male giraffes spar to establish this hierarchy. Sparring may involve the animals standing stiff-legged in parallel, marching in step with necks horizontal and looking ahead, rubbing and intertwining necks and heads, and leaning against one another to assess each other's weight. Most dramatic is "necking,", in which two giraffes, standing side-by-side, swing their heads at one another, using their horns to aim blows at the rump, flanks, or neck of their opponent. The animals rock to dampen impacts, but a hard blow can knock down an opponent.

Mature bulls that have established their dominance rarely resort to violent conflicts, but when they do these can be serious. The head of a giraffe bull gets heavier throughout its life, as it develops protective bony deposits, and can weigh 66 lb (30 kg) by age 20. A heavy blow to the underbelly of an opponent can cause considerable damage. Giraffes have a very thick hide as a first line of defense against the severe blows they can receive from other giraffes' armored heads.

Little is known of the okapi's behavior in the wild. However, captive studies suggest a dominance hierarchy. A dominant male displays by holding his head high and neck straight, while a subordinate signals submission by placing head and neck on the ground.

The fluid nature of giraffe society reflects their need to spend a lot of time feeding and to move independently between variable-sized trees. Their height and acute eyesight allow giraffes to maintain visual contact at long distances, and herds may disperse widely, only clustering at a particularly good food tree, or if bothered by lions.

Giraffe cows spend over half of their day browsing. Bulls spend less time feeding (43%), but more time walking (22% as against 13% for cows) in their perpetual search for females to mate with. Nights are mostly spent lying down, ruminating. Okapis are also most active during the daytime, but tend to follow well-worn paths through the jungle when feeding. In such a dense habitat, scent is believed to be important in locating breeding partners—okapis have glands on their feet, and have been observed urine-marking bushes.

Both species have a similar ambling gait, walking with their weight supported alternately on their left and right legs, like camels, while their necks move synchronously to maintain balance. The name giraffe may come from the Arabic zarafa, or xirapha, meaning "one who walks swiftly" or "graceful one." Giraffes can run at up to 35 mph (60 kph), with their hind legs swinging simultaneously ahead of and outside the fore legs, like a rabbit.

Lions are the main predator of giraffes, but hyena, leopard, and wild dog can also take young animals; up to 75% of calves die in their first year. Giraffes rely on their height and vision to spot predators and will defend themselves by kicking, but a pride of lions can take even a mature, healthy bull. Giraffe meat represents a substantial portion of lions' diet in some locations. Male giraffes are more vulnerable, because being more often alone they lack the benefits of group vigilance; in lion-rich areas, the giraffe population can be heavily skewed toward a majority of females. The okapi's main predator is the leopard.

Both giraffes and okapis are usually silent, but do have a range of vocalizations. Giraffe calves bleat or make mewing calls, and cows seeking lost calves bellow. Courting bulls may

cough raucously. Alarm snorts, moaning, snoring, hissing, and flutelike sounds have also been heard. Research suggests giraffes may communicate with infrasonic sound, as do elephants and blue whales—which suggests their social system may be more complex than once thought. Adult okapis may cough softly during rutting, and young okapis are noisier, with a repertoire of coughs, bleats, and whistles.

Feeding ecology and diet

The giraffe's unique physical form has evolved to exploit a 6 ft (2 m) band of foliage beyond the reach of any other browser except the elephant. A large bull giraffe, with a neck joint that allows its head to be extended vertically, can reach foliage 19 ft (5.8 m) high. Giraffes are almost pure browsers, feeding mainly on broad-leaved deciduous foliage in the rains and on evergreen species near watercourses at other seasons, and only occasionally eating grass, herbs, and fruit.

The giraffe's diet includes 100 species of tree but, in any one area, 40–60 will be utilized, with acacia and combretum being favored. They are selective feeders, using their narrow muzzles, flexible upper lip, and long, prehensile tongue to select the most nutritious leaves. The animal's molars crush acacia thorns, while smooth shoots are stripped of leaves by pulling them through a gap between the molars and canines. A male giraffe may consume 145 lb (66 kg) of food a day, but can survive periods of poor-quality fodder on as little as 15 lb (7kg). Giraffes are ruminants with a four-chambered stomach, and, unusually, they can chew cud while walking, which maximizes feeding opportunities. In mineral-deficient areas they sometimes chew on bones, and even carcasses, though this carries a risk of disease.

Okapi have also been recorded feeding on more than 100 species of plant, some of them poisonous to man. They also use their prehensile, 12-in (30-cm) tongue to pluck buds, leaves, and branches (used as well as for grooming). Okapis range about 0.6 miles (1 km) per day as they forage, and regularly eat sulfurous clay found along river banks to supplement their mineral intake.

Giraffes drink every two or three days if water is available, but extract much of their requirement from foliage. Their characteristic splay-legged, bent-kneed pose when drinking was thought to be necessary because of their long necks, but okapis adopt a similar pose, which suggests this is not the explanation. Drinking does make giraffes vulnerable to predators, and one animal will often keep watch while another drinks.

Reproductive biology

Giraffes are polygynous and breed year round, with a conception peak in the rainy season. Bulls always check the reproductive status of cows when they meet, by tasting their urine. Females reach sexual maturity at four to five years. Males compete for mating rights from age seven, but older, larger males have a strong advantage, and by the time a female in estrus is ready to mate, the local dominant male has usually asserted his rights without having to fight.

A male giraffe follows an estrous female closely, keeping other males away. The male's courtship behavior includes urine testing with a pronounced lip curl (called "flehmen"), rubbing his head on the female's rump and resting it on her back, licking her tail, and lifting his foreleg. After initially proving evasive, the female will circle, hold her tail out, and stand in a mating attitude to invite mounting.

Gestation lasts about 15 months, before a single calf (very rarely twins) is born, often in a favored calving ground. Giraffes have very long gestation periods compared to other ruminants, and bear—relative to the mother's body mass—very large young. These are very precocious, getting to their feet quite quickly. Giraffe milk is rich in fat, suggesting rapid growth of the calf. Mothers give birth standing up or even while walking, so the baby is dropped 6 ft (2 m) to the ground. A newborn calf is 6 ft (2 m) tall and weighs 110–120 lb (50–55 kg). In its first week, a calf lies out half the day and most of the night, guarded by its mother, which usually stays within 75 feet (25 m), but may leave to go to water. An absent mother always returns before dark to suckle the calf and stay with it overnight. After a few weeks, calves form nursery groups. Young start browsing after only one month, but are not weaned until one year, and may stay close to their mother until 22 months. Cows will usually conceive again about five months after calving. Young males remain in maternal herds until about three years old, after which they join bachelor herds and eventually leave the area. Females tend to remain in the range. Life expectancy is 20–25 years.

Okapi are believed to be polygynous, though courtship and mating rituals are known only from zoos. Females, sexually mature at two years old, remain in estrous for up to a month, advertising themselves by urine marking and calling. When a male is attracted, the two animals circle, sniff, and lick each other. The female is initially aggressive, while the male asserts dominance by extending his neck, tossing his head, and thrusting one leg forward. Male courtship displays include flehmen and showing his white throat patch. Mating then takes place.

A single calf is born between August and October after a gestation period of 14–15 months. It weighs 30–65 lb (14–30 kg) at birth, has a small head, short neck, long, thick legs, and a conspicuous mane. Mothers retreat into dense forest to give birth, after which the calf lies hidden for several weeks. It may spend 80% of its first two months in a hidden nest, growing

rapidly and avoiding predators. Calves are weaned after six months, but may continue to suckle for more than a year. They reach adult size after three years. Longevity is over 30 years in captivity.

Conservation status

Neither giraffes nor okapis are considered under immediate threat, but some giraffe subspecies are subject to intense pressure. The giraffe is classified as Lower Risk/Conservation Dependent by the IUCN. It is still common in east and southern Africa, but populations have fallen dramatically in West Africa, through over-hunting and habitat degradation. It used to be found from Senegal to Lake Chad, but is now only present in parts of Niger, where its conservation has been made a priority. Elsewhere, giraffes have survived where other large mammals have disappeared, perhaps because their height allows them to compete for food with domestic animals. The okapi is classified as Lower risk, Near Threatened, but accurate assessments of population size and trends are difficult because the animal lives in dense forest. Driven to extinction in Uganda in the early twentieth century, the okapi has been protected in the Democratic Republic of Congo since 1933. Habitat loss due to deforestation and poaching are its biggest threats.

Significance to humans

The giraffe has been revered by African cultures for millennia—it is depicted in early cave paintings and in ancient

Egyptian art. A captive giraffe was recorded in Rome in 46 b.c. Giraffe tails were highly prized by the ancient Egyptians and later cultures, being used as good-luck bracelets, fly whisks, and thread for sewing. Tourist demand for giraffe-hair bracelets continues to account for giraffe poaching even today, though meat and hide are more common motives. Giraffe are an important tourist draw in game reserves of east and southern Africa, and in southern Africa this has encouraged private game ranchers to introduce the species to land previously farmed for cattle. Giraffe have also been reintroduced to their former range in the southern Kalahari by conservationists. They also do well in zoos throughout the world.

The okapi was unknown to Western science until 1900. Henry Stanley heard of the okapi living in the dense Congo forests in 1890, but conjectured it was some kind of African donkey. Explorer Sir Harry Johnston journeyed into the Congo in 1899 and also heard about the animal, assuming it to be a species of forest zebra. Examination of skin samples at the British Museum led to mistaken announcements of the discovery of a new species of zebra. After obtaining a complete skin and two skulls, it was finally ascertained that the new species was a forest giraffe. Excitement over this "new" animal, which quickly assumed unicorn-like status, led to a rush by zoos to obtain specimens but there was a high mortality rate during translocation, and it was not until air shipment was introduced in the second half of the twentieth century that okapis could be moved with reasonable success. Many zoos now breed okapi successfully.

Species accounts

List of Species

Giraffe

Giraffa camelopardalis

taxonomy

Cervus camelopardalis (Linneaus, 1758), Sudan. Up to nine sub-species, but taxonomy is not fully agreed, and some subspecies hybridize. The reticulated giraffe (Giraffa c. reticulata) of north Kenya is most distinctive with a latticework of thin pale lines separating large chestnut-colored square patches. The larger Baringo, or Rothschild's, giraffe (Giraffa c. rothschildi) of western Kenya and eastern Uganda has chestnut patches separated by broader white lines but no spotting below knees. The Masai giraffe (Giraffa c. tippelskirchi) of East Africa has the most irregular pattern of star-shaped brown or tan spots. Other races include the West African giraffe (Giraffa c. peralta) in Niger, Kordofan giraffe (Giraffa c. antiquorum) of western Sudan, Nubian giraffe (Giraffa c. camelopardalis) in eastern Sudan and Eritrea, Thornicroft giraffe (Giraffa c. thornicrofti) in Zambia, the Angolan giraffe (Giraffa c. angolensis) in southern Angola, northern Namibia, and western Botswana, and the southern giraffe (Giraffa c. capensis) of South Africa, Zimbabwe, and Mozambique. Some authorities synopsize Kordofan and West African, Nubian and Rothschild's, and Angolan and southern giraffes, respectively.

other common names

French: Girafe; German: Giraffe; Spanish: Jirafa.

physical characteristics

13–18 ft (3.9–5.5 m) tall; weight 1,200–4,350 lb (550–1,930 kg). Large eyes and long black tongue. Male and female have

skin-covered horns. Coat is pale brown to chestnut patterned with lighter creamy buff.

distribution

Africa, south of the Sahara.

habitat

Arid and dry savanna with trees.

behavior

Gregarious, in loose-knit herds of up to 20 animals. Not territorial, but males have dominance hierarchy based on seniority.

feeding ecology and diet

A browsing ruminant that feeds selectively on leaves of more than 100 trees and shrubs, especially acacia and combretum species.

reproductive biology

Polygynous. Single calf born after 15 month gestation. Females pregnant in fourth year, then at least 16 months (usually 20) between births.

conservation status

Lower Risk/Conservation Dependent (IUCN). Largely eliminated from former range in western Africa, but common in suitable habitat in eastern and southern Africa. Population estimated at 141,000 (IUCN, 1998).

significance to humans

Hunted, often illegally, for meat, skin, and good luck charms. Translocated to stock game farms and zoos. Darting and translocation carries high risk of heart attack in older animals, so younger specimens preferred.

Okapi

Okapia johnstoni

taxonomy

Equus johnstoni (P. Sclater, 1901), Zaire.

other common names

French: Okapi; German: Okapi; Spanish: Okapi.

physical characteristics

Shoulder height 5–5.6 ft (150–170 cm); weight 462–550 lb (210–250 kg.). Females slightly taller than males. Long, black tongue. Male has skin-covered horns. Coat is dark chestnut to chocolate-brown with creamy white stripes on upper legs and white stockings.

distribution

Rainforest in northeastern Democratic Republic of the Congo.

habitat

Dense, moist tropical lowland forest near water, especially secondary forest.

behavior

Mainly solitary, except mothers with calves or mating pairs. Rarely forming temporary groups when feeding. Overlapping ranges, not territorial, but male dominance hierarchy.

feeding ecology and diet

A browsing ruminant utilizing well-trodden paths linking favorite feeding areas.

reproductive biology

Likely polygynous. Single calf born August–October after 14–15 months gestation. Females sexually mature at two years.

conservation status

Lower Risk/Near Threatened. Estimated at 30,000 in wild. Populations are highly localized but relatively common where they occur.

significance to humans

Okapi is a corruption of the native name, o'api. Historically, subsistence hunting using noose traps, pitfalls, and (rarely) driving animals into nets was probably at sustainable levels. Okapis are now protected, but poaching for bush meat poses a threat to long-term survival. An okapi breeding reserve was established in Epulu, Democratic Republic of Congo, to supply okapi with fresh genes for zoos and breeding centers, but the program was disrupted by war.

Resources

Books

Estes, Richard D. The Safari Companion: A Guide to Watching African Mammals. White River Junction, VT: Chelsea Green, 1999.

Lindsey, S. L., M. N. Green, and C. L. Bennett. The Okapi: Mysterious Animal of Congo-Zaire. Austin, TX: University of Texas Press, 1999.

Mills, G., and L. Hes. Complete Book of Southern African Mammals. Cape Town: Struik, 1997.

Periodicals

Bodmer, R. E., and G. Rabb. "Okapia johnstoni." Mammalian Species 422 (1992): 1–8.

Henk, P., H. van der Jeugd, and H. T. Prins. "Movements and Group Structure of Giraffe (Giraffa camelopardalis) in Lake Manyara National Park, Tanzania." Journal of Zoology 251, no. 1 (2000): 15–21.

Le Pendu, Y., I. Ciofolo, and A. Gosser. "The Social Organization of Giraffes in Niger." African Journal of Ecology 38, no.1 (2000): 78.

Ann and

Stephen B. Toon