Giraffes and the browse line

STAFF REPORTER for Namibian Sun

WINDHOEK

During the last few months of 2021, several farmers contacted Wildlife Vets Namibia about the fact that only a few giraffe calves make it to adulthood.

The veterinary company says giraffes are predominantly browsers; they mainly eat leaves and buds from trees and shrubs, and, during spring, herbs, flowers and fruit.

Giraffes are selective feeders, and their main food source are usually the Acacia, buffalo thorn, shepherd’s tree or witgat. Giraffes prefer to browse at a height of between 1.8 and 4.8 metres, which gives them little competition from other browsers.

“Unlike the elephant, giraffes are not well researched as being habitat engineers, but they certainly can have a devastating effect on certain tree species and can decrease species diversity, supress growth and kill trees.”

On the other hand, there is also evidence that browsing encourages new bud formation and shrub/tree growth, as some tree species respond to browsing by increasing in nutritional quality and better palatability.

However, excessive over-browsing can have detrimental effects on especially smaller trees and may in fact even kill trees.

“We believe the main reason for giraffe calves often not reaching adulthood is because there is simply not enough food.”

They explain that calves are weaned at about 6 to 12 months, when they are about 2.4 to 2.8 metres tall.

“Once the giraffe calves are weaned, they have to obtain all their food through browsing. If the browse line is so high that they cannot reach the leaves, their food intake will be insufficient to sustain themselves.”

Wildlife Vets Namibia says that trees, in an attempt to avoid over-browsing, start to produce tannins, which gives the leaves a bitter taste, resulting in giraffes stopping eating from that tree or shrub.

“This is an effective defence mechanism. However, in the absence of other food sources, browsers are forced to eat from those trees. In addition to the poor taste, tannins also reduce food digestibility which, in areas of insufficient browse availability, will force browsers to eat even more from these trees and shrubs.”

It says this can lead to poor body condition and a starvation syndrome (chronic tannin toxicity), which will be more of a problem in younger animals since the high browse line already deprives them of food.

Wildlife Vets Namibia suggests that farmers who experience a lack of giraffe calves reaching adulthood should have a proper look at the main tree species the giraffes forage on.

“If you see that trees on your farm are suffering by over-browsing – what to do? As said before, habitat is king, so leaving this as is and hoping for the best can be a dangerous strategy.”

They say farmers can reduce their giraffe numbers by culling or translocating them.

“If you feel the trees are perhaps temporarily suffering while waiting for the rains, one can build special giraffe restaurants. Note that it will take time before the giraffes get accustomed to feeding from these restaurants – start while the body condition is still good.”

Good supplemental foods for giraffes are, for example, camelthorn pods and lucerne.

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