Giraffe

Built by Gravity’s Rules

The giraffe (Giraffa camelopardalis) is the tallest land animal alive. Bulls stand up to 5.7 meters (about 18.7 feet) from hoof to horn tip and can weigh as much as 1,930 kilograms; cows run smaller, topping out around 1,180 kilograms. A giraffe’s life span is 15 to 20 years. Holding all that height up takes a neck built from just seven vertebrae, each of which can be over 10 inches (25.4 centimeters) long.

A Heart Built to Fight Gravity

A giraffe’s heart is about 0.6 meters (2 feet) long and weighs roughly 11 kilograms (25 pounds), and it drives an arterial blood pressure near the heart that runs roughly double a human’s, the extra force needed to keep blood reaching the brain against gravity. Lower down, a tight layer of skin and vessels that narrow ahead of the capillaries do similar work, keeping blood and fluid from pooling in the legs.

A Blackout That Never Comes A giraffe’s head swings through a bigger change in height than any other animal’s when it drops to drink, and it never faints doing it. A mechanical model of that head movement found that cerebral perfusion pressure, the pressure driving blood through the brain, falls as the head moves from upright down to level, then partly recovers as it keeps tipping further down. The researchers suggest its rise as the head comes back up may be an important mechanism for keeping the giraffe from blacking out.

An 18-Inch Tongue and a 16-to-20-Hour Workday

A giraffe’s prehensile tongue runs up to 18 inches (46 centimeters) long and works alongside flexible lips to reach around a tree’s long thorns. The tongue’s dark color is thought to work like sunscreen, protecting it from sunburn while it reaches for leaves. Giraffes spend 16 to 20 hours of each day eating, taking in up to 75 pounds (34 kilograms) of food and chewing cud on the move. A zoo study that filmed giraffes over 152 nights found they slept about 4.6 hours in every 24, in short, broken bouts, some of them standing up.

Lions, Kicks, and an Unsettled Family Tree

Adult giraffes are well able to defend themselves, and big enough that they don’t need to hide from predators. Lions are their main predators, with leopards and hyenas also known to prey on giraffes, and crocodiles taking them at waterholes; most of their predators target the young, sick, or elderly. When it has to, a giraffe defends itself with a deadly kick delivered karate-style with its front hooves, backed by a sprint clocked at a record 34.7 miles per hour (56 kilometers per hour).

The IUCN Red List rates Giraffa camelopardalis as Vulnerable, but a 2007 genetic survey found at least six distinct giraffe lineages across Africa with little evidence of interbreeding between them, and a 2016 study using multi-locus genetic data went further, arguing the differences are large enough that giraffes should be recognized as four separate species rather than one. The IUCN’s own giraffe experts, its Giraffe and Okapi Specialist Group, have concluded there are four species: the northern, reticulated, Masai and southern giraffes.