So how on earth does an animal even eat bones? Dropping the bones from high in the air to make pieces easier to handle is one step, but how do the birds actually ingest and digest a food source that seems so difficult to process?
Figure 9. A Bearded Vulture in the process of swallowing a bone whole.
- The first trick of bone eating is getting the nutritious marrow out.The vulture is equipped with a strong, narrow tongue. This allows it to reach down longer bone shafts. The tongue is also covered in grooves, maximizing the amount of marrow scraped out of the hollow bone. If a substantial amount of bone marrow is left behind, the bird will break the bone into smaller pieces and swallow them whole .
- After working to get the maximum amount of marrow, the bird often swallows the remaining bone. The Bearded Vulture can swallow these pieces with ease, as its esophagus is very elastic. It stretches to accommodate larger bone fragment or oddly shaped pieces. The walls of the esophagus are also thicker compared to those of other vultures, preventing potential internal injury caused by jagged edges of bone .
- Swallowing the oddly shaped bone chunks is difficult enough, so the Bearded Vulture lacks an anatomical feature that is common to most avian species: a crop! The crop is an expandable pouch that lies between the esophagus and the stomach. It is used by most bird species to store food. Bearded Vultures most likely lack this part of bird anatomy due to the difficulty that would be presented by getting bone fragments out of the crop itself. The intestine is also longer than that of other carnivorous species, to further aid in intense breakdown of bone material .
- All of these mechanisms for getting the bone swallowed are impressive, but they would be unhelpful if the bird was not able to efficiently digest the bone material. Bearded vultures have stomach acid with a pH less than one. This is incredibly acidic, which allows for the quick breakdown of the bone, skin, teeth and hooves. Large chunks of bone are usually dissolved within 24 hours .
Bone Processing in the Digestion System of the Bearded Vulture
Figure 10. The time latency of fecal production from a pair of Bearded Vultures after ingestion of a bone meal that shows bone digestion takes approsimately 24 hours (the hours after feeding at which fecal production is at its maximum) . Figure 11. A comparison of intestine length compared to body size of three different bird feeding types including the bone eating Bearded Vultures, other scavenging species such as the Griffon vulture and predatory species like the native eagles. The data shows that the intestine length of the Bearded Vulture is much longer, which allows the vulture to digest and process bone material .