Eating Poison Is the Black Rhinos’ Secret to Desert Survival
The desert has never been an easy place to make a living. There’s not usually much rain, and the vegetation is sparse and runty. Yet, when I was traveling not long ago in the arid landscape of Namibia, on the southwest coast of Africa, there was wildlife everywhere.
The animals seemed to have adapted to the desert in ways that flouted their very nature. One day, for instance, I watched as a giraffe spread out its front legs and canted its long neck down, not up, to browse on a stunted little thing known, unpromisingly, as the smelly shepherd’s tree.
Later, we stopped at one of the big clumps of milk bush that dot the landscape like haystacks in a Monet painting. The milk bush is actually a succulent, Euphorbia damarana, and it’s found only in this region.
Makumbi Swenyeho, a wildlife guide at Desert Rhino Camp, where I was staying, snapped open one of the pipe-like stems, which promptly bled a white latex liquid. It’s poisonous, he said, and effective enough that Bushmen hunters use it on the tips of their arrows. Contact with the skin can cause severe burning. According to local lore, 11 miners who had been brought into the area to work died just from eating food cooked over a fire built with milk bush branches.
But against all odds, black rhinos have adapted to make it one of their staple foods out here in the desert. They also like the haystack shape of the milk bush so much that they sometimes climb aboard and fall asleep. Locals refer to the flattened remains as a “rhino mattress.”
Gemsbok, big antelopes with a pair of three-foot-long unicorn horns on their foreheads, fled from us up the hillsides, looking like fanciful creatures out of a medieval bestiary. “They can go five or six days without water,” said Swenyeho. That’s remarkable not just because the daytime temperature in the Kunene region where I was visiting can rise to 122 degrees Fahrenheit, but also because a gemsbok can weigh up to about 500 pounds.
Now a new study in PLOS One reveals how the gemsbok do it. Like other antelope, they are primarily grazers, and get much of their water from grass. But the authors, from the University of Namibia and the Leibniz Institute for Zoo and Wildlife Research in Berlin, wondered what happens in droughts and dry seasons, when the grasses wither away.
The authors note that deserts are likely to spread as a result of climate change, leading to a loss of plant production, and perhaps also to species extinction.
“We therefore asked how antelope species respond to changes in food availability in semi-desert ecosystems,” the authors write. To find out they took tissue samples from gemsbok that had been killed by hunters, and profiled the isotopes left in the flesh by the foods the gemsbok had eaten.
The result: Gemsbok, like black rhinos, turn to the milk bush for sustenance in the dry season. Those pipe-like branches and the milky white liquid make up as much as 40 percent of their diet. No one knows how either species has adapted to handle the potent toxins in the milk bush. But the new study implies that, as the climate changes, other species hoping to avoid extinction may just have to figure out how to eat poison, too.