One of the distinguishing characteristics of a giraffe is its long neck. The neck has several important roles and specific functions:
With the aid of its long neck, a giraffe is able to reach leaves, fruit and flowers high up in Vachellia or Senegalia (formerly Acacia) and other sought after tree species. Giraffe are thus equipped to exploit a band of foliage beyond the reach of all other terrestrial browsers, except for elephant. Their 45 cm long tongue combined with a modified atlas-axis joint that lets the head extend vertically, further increases the height advantage. Giraffe can browse the crowns of small trees; big bulls can reach higher than cows. Giraffe feed mainly on broad leaved deciduous foliage in the rains and on evergreen species in other seasons.
Bulls, although also cows have been observed, have developed an elaborate ritualised fight called ‘necking’ that helps to most likely establish dominance. They repeatedly swing their long neck to deliver powerful head-butts to their rival’s body and underbelly. A reinforced skull usually absorbs the impact of these blows, but occasionally an animal is knocked unconscious and very rarely even dies during such a fight.
The giraffe’s height also helps it to keep a sharp lookout for predators across the wide expanse of the African savanna, essentially a tall ‘sentinel’.
A giraffe’s heart, which can weigh up to 11 kilograms, has to generate almost double the normal blood pressure of other mammals in order to maintain blood flow to the brain against gravity. In the upper neck, a complex pressure-regulation system called the rete mirabile prevents excess blood flow to the brain, when the giraffe lowers its head to drink. Conversely, the blood vessels in the lower legs are under great pressure (because of the weight of fluid pressing down on them). In other animals, such pressure would force the blood out through the capillary walls. Giraffe, however, have a very tight sheath of thick skin over their lower limbs which maintains high extravascular pressure in exactly the same way as a pilot’s G-suit.
Surprisingly, even with its long neck, the giraffe has the same number of vertebrae in its neck as humans and other mammals. Giraffe have seven cervical vertebrae, but each one can be about 25 cm long.