The Web of Life – Giraffes


A gentle giant and the world’s most graceful animal. ~Australian zoologist Julian Fennessy

The giraffe is an even-toed ungulate, native to the African savanna. There are 9 recognized subspecies, some of which may be separate species.

The giraffe is the tallest terrestrial animal and the largest ruminant. At a full-grown height of 5–6 meters, a giraffe neck may reach 2 meters, with legs equally long. Despite its long neck, a giraffe has the same number of neck bones (7) as most other mammals, albeit much longer.

Giraffes are especially fond of acacia leaves, which they can browse at heights other herbivores cannot reach. Giraffes generally like to eat with friends.

The mouth of a giraffe is extraordinary: thick, prehensile lips and a 50 cm prehensile tongue that can deftly grasp a branch and pluck away leaves while avoiding intervening thorns. Giraffes feed much of the day and often well into the night: consuming 34 kilos of leaves, shoots, and vines daily.

Giraffes are preyed upon by lions. Giraffe calves are savaged by wild dogs, spotted hyenas, and leopards.

Giraffe eyes are among the largest of land animals. Like other ungulates, giraffe have 2 eyelids, to protect and clean the eyes.

Giraffes have excellent trichromatic vision. Eyes are set laterally in their heads, providing such wide-angled peripheral vision that they can practically look behind themselves. This helps maintain herd cohesion and see predators at a distance.

Giraffes use visuals and subtle vocalizations to communicate. Staring is a favored form of communication. In spotting a predator, a steadfast gaze alerts other giraffes. A mother stares at other adults to warn them away from her calf.

Giraffes hum to each other at low frequencies using a rich vocabulary of notes at distinct durations, creating complex acoustic structures. (The giraffe vocal language is not at all understood; little research has been done on it.) Most giraffe humming occurs at night, when vision fails.

Giraffes also smell well enough, but a giraffe’s height distances it from the world of scents near the ground, where other mammals are immersed. Unlike most other ruminants, the giraffe has a dry nose and muzzle.

Good senses are something of a compensation for an unusual cardiovascular system. Being able to spot a predator far off saves running away.

The giraffe heart is 0.05% of body mass; roughly the same as a cow or mouse. To pump blood up its long neck, a giraffe’s heart pumps at 2–5 times the blood pressure of humans, beating 2.5 times per second (150 beats per minute). To accommodate the strain, the wall of the giraffe heart is 7.5 cm thick.

Giraffe blood vessels are thick to withstand the pressure and prevent leakage in the long passages to the head and hooves. Valves in the neck prevent a giraffe from fainting from excessive blood flow when it lifts its head from taking a drink.

For such a fast heartbeat, the volume of blood pumped is modest. This curtails distance running: the heart cannot deliver enough oxygen to power extended exertion. Giraffes can run faster than horses for a hundred meters or so.

A giraffe’s patchy coat offers some camouflage by blending in with the blotches of light and shade in the woods. An adult giraffe standing amid trees and shrubs is hard to see even a few meters away. While each giraffe has its own individual coat pattern, giraffes inherit their spot patterns from their mothers. This affords ready family identification.

The characteristic scent of a giraffe owes to at least 11 aromatic chemicals in the fur which act as parasite repellents. Males are more odorous than females. There probably is some sexual function to a giraffe’s scent.

Typical of mammals, adult female giraffes are more gregarious than males. Lady giraffes form close friendships that can last years. Females provide emotional support for each other.

Social cohesion in giraffe groups of 10–50 individuals is partly maintained by bonds between calves. Mothers and their young make for the most stable social groups, which may last for months.

Mothers with offspring move and browse together in nursery herds. A mother may sometimes leave her calf with a friend while she enjoys some time alone foraging. Adult males play no role in rearing the young, though they are friendly with calves.

Giraffes have a lifespan of up to 25 years. Few live that long.

Mothers grieve for the loss of their calves to predation. There is much to grieve. More than half of all calves are killed in their 1st year, even as mothers will valiantly fight for their young, with kicks powerful enough to break a lion’s jaw. Only about 30% of giraffes born survive to adulthood.

Males have a dominance hierarchy relating to mating rights. Bulls generally gain rank with age.

Into adulthood, the twin cones on the top of a maturing bull’s head thicken and lose their charming tufts. The middle of the forehead grows a bony mass. The neck muscles strengthen. A bull’s posture becomes more proudly erect.

Dominance clashes among bulls can be fierce. A male uses his massive neck as a sling to slam his head into a rival. This can break a rival’s neck and may even be lethal.

A giraffe’s neck is instrumental in maintaining balance. It assists in moving forward and is necessary in helping a giraffe stand up.

To get off the ground from lying down, a giraffe throws its head and neck toward its legs, using the force of momentum to bring it onto its stomach. Another throw – this time toward the tail – lets a giraffe stand up.

Like elephants and other large herbivores, bulls have unsynchronized rutting periods, but for much shorter durations. Thus, dominance among males is unstable.

Young bulls in their first rutting mimic the demeanor of their elders: heads held high, females pursued, prodded, and female urine sniffed for signs of estrus. Should a dominant bull saunter by, a young male drops its poses and tries to make itself looks small and innocent.