The sight of a giraffe browsing on the leaves of a majestic acacia tree is synonymous with Africa. Giraffes have a fondness for the tree that is unrivalled by any other, and this fondness results in a fascinating ‘to and fro’ relationship between fauna and flora.
Giraffes can eat as much as 29 kilograms of acacia leaves and twigs daily. Herds of three or more giraffes spend hours browsing in acacia thickets, greedily gobbling up as much of the delicious foliage as they can. They don’t have it all their own way however…
Over time, the acacia tree has developed several clever defence mechanisms to prevent giraffes from munching on them unabated. As I’m sure most travelers to Africa can attest to (after painfully stepping on a fair few), the acacia does not mess about when it comes to thorns. Taking their name from the Greek word for thorns – akis – some species grow thorns that are as long as 8-10cm, and sharp as a knife.
The wily giraffes have developed a counter to this though, by way of their incredible tongues. The giraffe’s tongue is about 45cm in length and highly prehensile. This allows the animal to successfully negotiate the bigger thorns and pull the leaves from the branch. Coupled with tough lips and palate, the giraffe has seemingly overcome this particular hurdle. But the acacia trees have a plan B.
Just in case their thorny perimeters are breached, which they often are, the acacia trees have developed a further defense – the release of tannins. Tannins are water soluble, carbon based compounds found in plants that are very important to man. Their chemical and physical properties allow the binding of alkaloids, gelatine and other proteins in the making of leather, or tanning. They are also used in food processing, fruit ripening and the making of wine and cocoa. But they’re no good to giraffes!
Besides tasting awful, tannins inhibit digestion by interfering with protein and digestive enzymes and binding to consumed plant proteins making them more difficult to digest. What’s even more amazing is that acacia trees within 50 yards react to the release of the tannin by their neighbour and jump on the bandwagon by emitting their own. The simultaneous tannin release by all nearby acacias essentially thwarts the greedy giraffe(s), who must now travel upwind to trees that have not yet ‘caught wind’ (irresistible really!) of his insatiable appetite.
So next time you see a giraffe browsing on an acacia, using his amazing tongue to navigate the devilish thorns, bare in mind the ace up the acacia’s sleeve – it’s only a matter of time before it’s played.