Feeding choices and impacts of extralimital giraffe on two keystone tree species in the Kgalagadi National Park

Giraffes may choose easier thorns over richer leaves. Along the Auob River in the Kgalagadi Transfrontier Park, introduced giraffes fed heavily on grey camelthorn, even though neighbouring camelthorn offered more protein. The difference between the trees’ defences suggested that reaching a meal could matter as much as its contents.

Edmund February, Eleanor Shadwell, Storme Viljoen and Dawood Hattas compared areas with different giraffe densities. They counted tracks and dung, photographed 36 trees to measure canopy damage, and analysed leaves and fresh dung for chemical signatures indicating diet. They also compared leaf protein, defensive chemicals and the length, thickness and spacing of thorns.

The isotope model attributed roughly four-fifths of the diet to grey camelthorn. Its canopy suffered more damage where giraffes were common, while ordinary camelthorn had stronger physical defences despite its higher leaf protein. This supports, but does not experimentally prove, the idea that tougher thorns discouraged feeding. The team found no clear corresponding reduction in young-tree establishment. The immediate lesson is about selective pressure: giraffes introduced for tourism do not spread their browsing evenly, and their preferred trees can bear a disproportionate share of the damage.