The Bone Eating Bird

The Bearded Vulture

Gypaetus barbatus

Some animals may come across a carcass that has been picked clean by other carnivores and simply move on in search of some other food source. However, there's on scavenger that would rather wait until only the seemingly inedible is left! The Bearded Vulture is the only bird in the world known to thrive on a diet consisting primarily of bone [2]!

In fact, Bearded vultures actually prefer bone even when fleshed carcasses are presented as an option. They largely prefer limb bones and ribs, as they house the most nutrition. It is estimated that bone marrow, mainly from ungulates like goats and sheep, makes up 70% or more of the vulture's diet [3], but how do the vultures get the marrow out?

Smaller bones can be crushed via the beak, but larger, denser bones must be dropped onto rocky landscapes, called ossuaries, during flight [4]. The vulture then flies down to the site at wich the bone has broken, and consumes the marrow. The process may be repeated more than once for the same bone. See the Bearded Vulture in action here!

Figure 1. A mature Bearded Vulture [14]. Figure 2. A Bearded Vulture releasing a bone mid-flight [15].

The Bearded Vulture (Gypaetus barbatus), also known as the Lammergeir, is a raptor native to Europe, Asia and Africa. Monogamous pairs establish huge territories in mountainous open ranges. They were almost completely eradicated in Europe, as they were perceived as a threat by native peoples. Now they face habitat degradation, food shortages and toxic chemicals set out to exterminate vermin [1]. There's a risk that this great animal will soon become endangered.

Mature Bearded Vultures have white or yellow feathers on the head, with red eye rings and black 'masks'. This species got its name from feathers train off the beak to form what looks like a beard. Their bodies are actually white, so why does the bird in Fig. 1 look orange? The feathers are actually stained with iron rich mud that the birds bathe in, resulting in a brown tint! Their wing and tail plumage is black. They have a wingspan of approximately 2.7 meters (8.8 feet).

So why would a vulture scavenge on seemingly dry bones when they could go for some real meat? To further understand the unique food choice of these beautiful birds, the bone dropping and feeding behavior will be investigated via Tinbergen's four questions:

    1. Phylogeny investigates how the behavior in question has evolved.
    2. Ontogeny investigates how the behavior develops and can apply both to embryonic and genetic development, as well as development over the organisms lifetime.
    3. Mechanism investigates the structural component of the behavior.
    4. Adaptive value investigates what the behavior does to increase the organism's fitness.