Dave Taylor's African Safari: Scavengers and Decomposers - Birds: Vultures

Scavengers and Decomposers
Birds: Vultures
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The Old World vultures (i.e., those of Eurasia and Africa) are not related to the New World vultures (i.e., the Americas). New World vultures, such as the Turkey and black vulture, are more closely related to storks. The Old World vultures are placed in the same family as eagles and harriers (hawks). There are 16 species of Old World vultures, six of which are found in the Serengeti-Mara ecosystem.

Many species have adapted their features to allow them to feed on the carcasses of larger mammals. Some species have a long, hooked beak to tear open the skin of the dead animal. Most lack feathers on their heads and necks. If they were feathered there, they would build a layer of blood and waste as they reached inside the corpse to feed. This covering of gore would soil the feathers and cause the bird to get infections. Vultures are clean birds and having bare skin allows them to remove infectious material far more easily than they could if their heads and necks were feathered.

The talons of most vultures are not suitable for grasping and killing prey.

Vultures are adapted as well to a life that often requires them to go for days without food. They are large birds and can fast for a week between meals. When they do find a carcass, they bolt down up to 1.5 kilograms (3.3 lb.) of meat (depending on the species). Vultures have a crop and gizzard that can hold this large quantity of meat. They also have a gland system that secretes abundant digestive juices, which makes putrid and poisonous meat harmless.

A well fed vulture is a heavy vulture and it will normally fly to a safe, nearby roost where it will digest its meal. Like most birds, vultures lack a bladder, and within short order they void their waste, producing a stream of white guano.

When feeding young chicks at a nest, vultures produce a pre-digested "rearing broth" from the carrion they eat. Later, they feed larger chicks by regurgitating larger food that they carry to the nest in their crops. Young vultures, especially Griffon vultures, do not have to be fed daily.

Vultures lay one or two eggs. Usually only one chick survives. The older, larger one forces its smaller competitor out of the nest.

Few animals prey on vultures.

(see also Appendix IX: Comparison chart of Serengeti-Mara’s Birds of Prey)

Feeding Order

There is a well defined feeding order among the Serengeti-Mara's six species of vultures. White-backed and Ruppell's Griffon vultures cannot open a carcass. They must wait until this is done either by the predator (lion, spotted hyena, wild dog, jackal) or until the lappet-faced and white-headed vultures arrive.

The lappet-faced and white-headed vultures both possess longer, more powerful, curved beaks than any of the other vultures. They are capable of tearing open the skin and exposing the flesh which they eat. There are usually no more than four or five lappet-faced vultures at a kill.

White-backed and Ruppell's Griffon vultures have similar but less powerful beaks. They feed on the softer tissues inside the carcass. Both of these species have long, bare necks that allow them to reach well into the open cavity. They also have specially adapted tongues for removing the meat from the bones. Their tongues are gutter-shaped, with rows of long "horny, teeth-like" projections growing on it. These point backward and downward and help force the food into their gullets.

It is these two species that overwhelm the carcass and quickly reduce it to a pile of bones. Often, there are so many of these vultures at a kill that they succeed in driving the predator away. At first, one or two arrive, but soon others arrive and slowly an audience of vultures waits for their chance to feed. They know how close they can go. A pride of hungry lions will tolerate no vulture at the kill, but a single well fed lion or lioness can be encouraged to leave. The same is true of spotted hyenas. A large clan will leave little for the vulture.

A single cheetah can often be driven from its kill without much trouble. Cheetahs try to hide their kills from vultures so that they won't draw in lions and spotted hyenas.

Both the white-backed and the Griffon vultures’ feeding habits result in the birds’ necks and heads being covered with gore. If left on, it would decay and become infected. As a result, these birds bathe in water to clean off the filth. They are, in fact, very clean birds.

The final two species of vultures are more specialized. The hooded and the Egyptian vulture are the smallest of the vultures and lack powerful bills. They pick up the scraps around the carcass. The hooded vulture searches the ground for dropped pieces of meat while the Egyptian gleans the last scraps from the bones.

In the early morning, it is likely to be one of these two species that will be seen at a kill. They are lighter birds and don't need to wait for the thermals in order to be airborne.

Almost two thirds of all of the vultures in the Serengeti-Mara are white-backed vultures. One quarter are Ruppell's Griffon vultures and lappet-faced, a twelfth or less are hooded, while Egyptian vultures account for less than one hundredth. Hooded vultures account for the rest.

In Africa, it is unusual to have all six species in the same area. That the Serengeti-Mara can support populations of all six is a testament to the richness of this ecosystem. The six species can be divided into three sets of competing vultures, each pair occupying a similar niche. Lappet-faced and white-headed vultures compete to open the carcass. White-backed and Ruppell's Griffon vultures compete for the inside tissues. The last two compete for the scraps. In most areas, only one species from each pair is found.

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