Down to the Bones: Animal Osteophagia

Leopard tortoise
Photo: Thomson Safaris guest, Tina Siebold

Ever wake up with a strange, overwhelming craving for bananas, or a thick cut of steak, or an extra-salty bowl of miso soup?

Some of that might just be because those things taste good, but specific cravings can be our bodies’ way of telling us that we need a certain kind of nutrient—potassium, or iron, or sodium—and that we’re not getting enough.

For some of the herbivores of the Serengeti, the craving they wake up to is an overwhelming urge to crunch down…

…on a bone.

Bone-eating, known as “osteophagia,” is more commonly observed in predators. Their stomachs and jaws are designed to deal with digesting meat and bone, and some of them—like hyenas—even eat prey whole.

Herbivores, on the other hand, aren’t equipped to chew through bone. But they still need the nutrients it contains in abundance—including calcium and phosphorous—nutrients which aren’t readily available in their diets of scrub, grasses, and tree leaves.

So some of them—including giraffes, cape buffalos, several antelope species, and zebras—gnaw on bones instead.

Though it’s not a very efficient process (without the same digestive acids as predators, drawing nutrients from the bones is difficult, at best), it’s been observed often enough, across enough different species, for scientists to conclude that it’s fulfilling a nutritional need for the creatures.

Perhaps one of the strangest osteophagists is the leopard tortoise.

Its jaws are too small to pick up anything other than the smallest bones (which aren’t easy to find), so it makes do with a double-dose of phagia: osteophagia via coprophagia.

Coprophagia is the consumption of dung, and it’s often practiced by young herbivores (who need a “dose” of their parents’ gut bacteria in order to effectively digest their food), as well as scavenger species.

The tortoises practice it very selectively: they only eat hyena scat, and only very occasionally. That’s because hyenas eat their kills whole, chewing through enough bone with their meals to turn their scat completely white.

For us, the white scat might just seem like an oddity, but to the tortoises, it’s like a giant vitamin, packed with the calcium and phosphorous their bodies need.

Apparently, when it comes to animals—and our occasionally confused classifications of them as strict “herbivores” and “carnivores”—we just haven’t accounted for taste.