Sweet giraffes and thorn trees

It had rained and the clouds were departing when we drove through an area of thorn trees that have a particularly sweet scent. You can smell the delicious aroma before you see them. Once amid the bright green leaves and yellow blossoms we saw a mother giraffe and her curious young calf. The calf was adorable and had long black tufts on his ossicones that were all wet and wavy from the rain. The ossicones of adult female giraffes have short black hair, while males are usually bald from sparring. However, all giraffes are born with long black hair on their ossicones.

Both mother and calf were relaxed and curious enough for us to step calmly off the vehicle and photograph them from ground level up, which is a good way to get perspective on their towering height.

Giraffes and sweet thorn trees have an intricate, evolving relationship. Giraffes are partial to their leaves and have evolved adaptations like long necks and tongues to reach and grab leaves, even around thorns. These thorn trees, in turn, have developed defence mechanisms, including thorns, tannins, and even ant symbiosis, to deter over-browsing by giraffes and other herbivores.

Let’s take a more detailed look at their interaction:

Giraffes have long necks and tongues to reach high into trees and access leaves that are otherwise out of reach for most other animals. They can use their tongues to pull leaves from branches, even those with thorns. They have thickened lips and hardened palettes that protect their mouths and throats from sharp thorns.

Thorn trees have their sharp, protective structures to deter many herbivores from eating the leaves. In addition their leaves also have tannins. These tannins have a bitter taste and can interfere with an animal's digestive system, making the leaves less palatable and even toxic in high concentrations.

Ethylene signalling is when a tree is being browsed, it releases a chemical signal (ethylene) that alerts neighbouring thorn trees to prepare for potential attack from herbivores by releasing more tannins.

Another interesting defence is that some thorn trees have a mutualistic relationship with certain ant species. The ants live in swollen thorns, feeding on nectar produced by the tree, and in return, they protect the tree by attacking any animal that tries to eat its leaves.

This interaction is a classic example of co-evolution, where the adaptations of one species (giraffe) have influenced the evolution of another (Vachellia thorn trees). Giraffes have adapted to overcome the tree’s defences, while the tree has continuously evolved new defences in response. This ongoing process shapes the distribution and abundance of both species in their environment.

Knowing a little about what’s going on in the background to a sighting like this of a mother teaching her calf how to browse on the trees makes the scene that much more special. However, I think there was another silent game at play here – that of the fluffy-topped baby giraffe stealing everyone’s hearts!