Giraffe

The giraffe is the tallest animal that has ever lived on land, and almost everything about its body is a solution to the engineering problem of being that tall — especially the problem of moving blood.

Overview

Giraffes browse the open savannas and dry woodlands of sub-Saharan Africa, feeding at a height no other animal can reach. Their height also serves as a watchtower: a giraffe can see a lion coming from a kilometre away, and other grazers keep an eye on the giraffes for exactly that reason. Depending on how you count, there are one to four species, distinguished by coat pattern and range.

The neck

A giraffe’s neck can be 2.4 m long, yet it contains the standard mammalian seven vertebrae — each stretched to a huge length. The neck is used for more than feeding: males fight by “necking,” swinging their heavy, horn-tipped heads at each other like clubs in contests that can knock an opponent unconscious.

The plumbing

Pumping blood two metres straight up to the brain requires the giraffe’s heart to generate blood pressure roughly twice that of a human. Several adaptations stop this from causing damage:

• A large, thick-walled heart — about 11 kg — with a small, powerful left ventricle.
• Tight, inelastic skin on the lower legs that acts like compression stockings, preventing blood from pooling and fluid from leaking out.
• A pressure-buffering network of vessels (the rete mirabile) at the base of the skull that absorbs the surge when the giraffe lowers its head to drink and prevents a blackout when it lifts it again.

Diet

Giraffes are browsers, not grazers. They eat leaves, shoots, flowers, and fruit — above all from acacia trees, whose thorns they navigate with a tough, mobile, 45-centimetre tongue and a groove in the roof of the mouth. A giraffe processes around 30 kg of foliage a day and gets so much moisture from leaves that it can go weeks without drinking, which is fortunate because bending down to a waterhole leaves it dangerously vulnerable.

Behaviour and life cycle

Giraffes live in loose, ever-changing herds with no fixed leadership. They are nearly silent to human ears but communicate with infrasound below our hearing range. They sleep very little — often just half an hour in a day, sometimes in brief standing “micro-naps.”

A calf is born after a 15-month pregnancy, dropping roughly two metres to the ground as the mother gives birth standing up. It can stand within an hour and run within a day, but the first few months are deadly — more than half of calves are killed by lions, hyenas, leopards, and wild dogs. Survivors gather in nursery groups called “calving pools” watched over by a rota of mothers.

Threats and conservation

The giraffe is Vulnerable and declining, with numbers down around a third in three decades:

• Habitat loss and fragmentation as savanna is converted to farmland and cut by fences and roads.
• Poaching for meat, hides, and tails.
• Civil unrest in parts of the range, which removes protection and increases hunting.

Conservation attention has lagged behind the scale of the decline — hence “silent extinction” — but dedicated giraffe organisations, translocations to rebuild lost populations, and community conservancies are beginning to turn some regional trends around.