The High Life: Giraffes

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These lanky browsers are ever popular with readers and here we present a stunning portfolio by the husband and wife team of Michel and Christine Denis-Huot. Accompanying these studies of giraffes, all taken in Kenya's Samburu National Reserve, are notes on the behaviour and biology of these fascinating mammals compiled from Richard Despard Estes' comprehensive work The Behavior Guide to African Mammals.

Growing tall gave the giraffe access to a two-metre band of foliage beyond reach of all other large browsers but the elephant. Aided by a 45-centimetre tongue and modified neck joints that enable the head to tilt to the vertical, a giraffe can feed on the crowns of small trees. Big bulls can reach up to 5.8 metres, nearly a metre higher than cows. Where a choice exists between high and low browse, there is a clear ecological separation between the sexes, the bulls browsing high while females concentrate on regenerating trees and shrubs below two metres. The sexes of distant giraffes can usually be predicted by whether the animals are feeding high or bending low.

Differences in feeding ecology as well as lower vulnerability to predators (based on size and absence of parental responsibility) allow males to enter taller and denser woodland more readily than females, leading also to a measure of spatial separation of the sexes.

Apart from its size, shape and markings, one of the most distinctive features of the giraffe are its stubby, tufted horns. Unlike all other horned mammals, the giraffe has the main pair of horns present even in the embryo. They are formed of cartilage from a layer of skin unattached to the skull and lie flat, presenting no obstacle to birth. Within a few days, however, they stand erect and appear prominent, mainly because of terminal tufts of long hair. While growth proceeds from the base, bone deposition begins at the tips and proceeds downward. Fusion with the skull occurs at 4-4.5 years in males and after seven years in females.

Rather than attaching to the frontal bones, as in deer and antelopes, the giraffe's main pair of horns take root further back in the parietals. Male horn growth continues through a unique process whereby bone of skin origin is deposited over the whole surface of the skull except where muscles attach. Gradually the male's head becomes a massive knobbed club which is used to gain the dominance that spells reproductive success.

Position in the male dominance hierarchy is largely a function of seniority and between peers is decided usually before maturity through contests in the bachelor herds. The challenge to a duel begins with an apparently nonchalant approach. When close, the challenger raises his head and stands in the erect posture facing his opponent. If the other responds in kind, they then stalk forward stiff-leggedly and stand parallel, or they may march in step with necks extended horizontally, looking straight ahead. At low intensity, they proceed to rub heads and necks gently together and may lean heavily against each other with ears flapping and rub shoulders or flanks - probably assessing their comparative weight and strength.

If the contest becomes more intense, blows begin to be exchanged, aimed at the rump, flanks, or neck. Before giving or receiving blows, a giraffe braces himself and then draws his neck sideways and swings upward and backward over his shoulder to strike his opponent with the parietal horns, thereby concentrating the blow in a small area. But blows seldom land solidly, for each does his best to avoid being hit by moving his neck away at the last moment, meanwhile getting ready to return the blow.

Movement and counter-movement appear rhythmical and synchronized, imparting the sinuous grace of a stylized dance. There may be long pauses between blows when the animals stand motionless.

The force of a solid blow is literally staggering. The heavier the skull and the wider the arc of the swing, the harder a giraffe can hit - hence the advantage of age, height and weight. Mature bulls know their place in the hierarchy and normally avoid confrontations, even when an oestrous female is at stake.

A serious fight is apt to be brief but violent and involve a stranger with the top male in the local hierarchy. After a few heavy blows, one gives up and runs away. In one case a bull was knocked senseless and lay stretched on the ground for 20 minutes before recovering.

Even when eating up the ground at 50-60 kilometres an hour, the giraffe is so long-legged that it appears to be moving in slow motion. In fact, the giraffe has only two gaits, an ambling walk and a gallop. When walking, the entire weight is supported first on the left legs, then on the right legs, as in a camel. Otherwise, the long limbs on the short trunk would interfere with one another. The neck moves in synchrony with the legs and helps the giraffe maintain its balance. At a gallop, forefeet and hindfeet work together in pairs as in a running rabbit, the hindfeet landing outside and ahead of the forefeet.

The giraffe is not only physically but also socially aloof, forming no lasting bonds with its fellows and associating in the most casual way with other individuals whose ranges overlap its own. Giraffes rarely group closely, except when browsing the same tree, when the approach of a predator makes them nervous, or in large numbers in open tree grassland. Even at rest they stay more than 20 metres apart. A dozen feeding giraffes may be spread out over an area greater than a kilometre - can such a collection of individuals be called a herd?

There is no leader and a minimum of co-ordination in their movements. Yet even widely dispersed giraffes may well maintain visual contact, thanks to their lofty vantage point. Rival bulls recognize and react to one another from a long way off, demonstrating the capability of long-distance communication.

Except when guarding a newborn offspring, females are rarely sighted alone and usually there are other females somewhere within view. Mothers with small calves are most likely to associate. The tendency of calves to cluster together in crèches anchors mothers to the same locality. In addition, females return faithfully to particular calving grounds. Even so, giraffe herds are so fluid that a Serengeti cow who was seen on 800 consecutive days was only twice found with a group whose composition remained unchanged over a 24-hour period.

The fact that a few adult individuals are regularly found associated can probably be explained as the occasional continuation of social bonds between mothers and daughters, which typically remain within their natal home range. Though behavioural interactions between females are rarely observed, the existence of some sort of hierarchy is indicated when one cow yields its feeding place at the approach of another.

Males tend to associate in bachelor herds beginning at puberty (three years), and to emigrate outside their natal ranges. As males mature they become increasingly solitary, dividing their time between feeding and monitoring the reproductive status of the females within their core ranges. These tendencies, like the males' preference for more heavily wooded habitat, promote sexual segregation of adults. However, males in herds or alone frequently mingle with females and young. Consequently, giraffe herds may contain almost any possible combination of sexes and ages at any given moment - and will almost certainly not remain in the same configuration for many hours. In living the high life, variability is the only rule.

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