Where Do The Bones Go?

Have you ever wondered what happens to all the bones? Animals are dying all the time, and when they die their soft tissues are eaten by predators and scavengers, picked off by birds, ingested by insects, and decomposed by microorganisms. This leaves just bones, like those of a rabbit shown below. But we don’t see bones littering the landscape, so what happens to them?

First let’s consider small animals. When a tiny creature such as a vole is killed by a predator, the catch is swallowed whole and the bones are crushed and partly assimilated. Undigested bone fragments are eliminated in scat (or pellets if the hunter was a hawk or owl). You can see small bone fragments in the red fox scat shown below–there’s also plant material, tiny hairs, and what appears to be a whisker. Scat like this will eventually be weathered and dispersed into the soil. Even if a small animal isn’t completely consumed immediately, its remains will be broken down, dispersed, and probably hidden from our view by its surroundings.

But what of larger animals whose carcasses would be more obvious? Deer immediately come to mind, but the question also applies to bears, coyotes, woodchucks, raccoons, and other similar sized animals. We do occasionally see the remains of recently deceased animals, like the deer carcass in the next photo, but why don’t we see piles of old bones lying around everywhere?

The answer has to do with the nutritional value of bones. The deer femur in the next photo was cracked open by a coyote to get at the marrow. (I say coyote because the only other animal in our region which is powerful enough to break a deer leg bone would be a bear, and there were no bears in the area where the bone was found.) Toward the upper end of the larger piece you can see some striations which were probably made by the coyote’s molars as it worked at the bone.

We sometimes see evidence of the utilization of bones this way in scat. The coyote scat in the next image contains an abundance of deer bone fragments and deer hair. The hair would have cushioned the sharp bone edges and prevented injury to the animal’s digestive system. It wouldn’t take long for bone fragments like these to be hidden in the upper layers of soil.

In addition to marrow, bones contain calcium, phosphorus, and other minerals which may be lacking in the diets of wild animals. Mineral deficiencies are especially likely for herbivores. Many animals supplement their nutrient intake by chewing on bones, and they usually choose less daunting ones such as scapulas, ribs, and vertebrae. The bones of birds, reptiles, and smaller mammals such as rabbits can also be utilized by less powerful animals. Even deer have been observed chewing on bones. This kind of chewing may not leave obvious signs–just ragged edges, missing ends, or random gouges.

Rodents also gnaw on bones, and the evidence of their activity is often more conspicuous. In the next photo you see a segment of deer leg bone lodged on a midden at the base of a Norway spruce tree. Middens, piles of discarded cone cores and scales, are created when a red squirrel repeatedly uses a favorite perch to feed on cones. The red squirrel that claimed this tree must have used the same perch to work on the bone.

In the next photo you can see the grooves made by a squirrel’s incisors as it chiseled off bone shavings.

Smaller rodents, like voles and white-footed mice, leave finer grooves like the ones in the next photo.

These creatures weren’t after marrow, since the bones were relatively old and the marrow had been removed long ago. This behavior is probably driven in part by the need to supplement their mineral intake, but rodents also chew on bones (and antlers as well) to maintain their teeth in good condition. Their incisors grow constantly, and are subject to malocclusion if not shaped and worn down with regular gnawing. The same is true for rabbits and hares, which are also known to gnaw on bones.

As time passes carcasses are pulled apart and bones are cleaned of soft tissue, scattered, broken, crushed, pulverized, chewed, and ingested by many different animals. Rather than piling up as useless cast-offs, animal bones gradually disappear as they are utilized by living creatures. Animals are part of the web of life both while they are alive and after they are dead.