Sunday, January 20, 2002		Nature

They feed on the dead
Nutan Shukla

RELATED to birds of prey, like eagles, falcons and hawks, vultures are highly developed as ‘professional’ scavengers. Usually carcasses have several species of vultures in attendance, each type specialised to exploit different parts of the body and, therefore, not in competition with each other. This phenomenon is more evident in East Africa where many species congregate on the same corpse to feast. Griffon vultures have a sharp-edged bill for cutting meat and a serrated tongue to help swallow it quickly. The crop (a pouch in a bird’s gullet where food is prepared for digestion) can take a quarter of the bird’s body weight in food. This species feeds on soft, fleshy parts, while others, like the aggressive, lappet-faced vultures, go for the skin, tendons and other, coarse tissue. In fact it is the lappet-faced vulture that opens up the body, a task that others cannot do, thereby exposing the flesh inside for others. They also eat the coarse tissues that other species cannot digest. Once the internal parts are exposed every species eats what it chooses. The Egyptian vulture, which is smaller than other species, picks up the leftovers with its thin beak. The head and neck of some species, like lappet-faced and white-backed vultures, are naked, an adaptation enabling these scavengers to insert their heads deep into a gory carcass without spoiling the plumage with blood and flesh.

Vultures are divided in two groups, namely Old World vultures and the New World vultures. The former are those that are found in Europe, Africa and Asia, whereas the latter are the North, Central and South America. In this article we are dealing with the vultures of the Old World only.

It is generally believed that these birds possess very keen eyesight. Now it has been proved that it is not true. In fact, they have reasonable eyesight, not much better than our own. Now the question is how do they spot a carcass from such a great height, even if it is hidden by a canopy of trees. The answer lies in the fact that they are very good at keeping a watch on predators which hunt themselves, like lions and ground-living, four-legged scavengers, like hyenas, jackals etc, and their own cousins dropping down to feed. An ‘eye-spy’ chain of vultures watching others can have birds homing in on a carcass from several miles away. Lions and leopards often haul their kills into the shelter of bushes to prevent the inevitable invasion.

Many bloody battlefields have been visited by vultures during wars and badly injured soldiers, unable to move or fight back, were often in danger of being attacked and torn apart by the birds. Ancient Abyssinian armies were said to have been accompanied overhead by flock of vultures, and shooting parties were dispatched to scare off the flocks during the Crimean War.

As far as eating is concerned, if these birds do not find a carcass, they take to eating dung; but not just any old dung, they prefer that of the big cats, ignoring dung from dogs and hyenas. Big cats, such as lions, do not digest their food as well as dogs do, and so lion dung has about 10 per cent more undigested food available for vultures. These birds, like the dogs, also have a highly efficient digestive system and are able to extract the last ounce of nutrients from what seems at first sight to be an unlikely source of food.

Vultures are large and heavy-bodied birds. Most are carrion feeders. Many species have a bare neck which is the most vulnerable part of their body. To protect it from attack they roost at night with their neck tucked into the wings. They have very slow wingbeats; their flapping rate is as low as one beat per second, whereas some hummingbirds beat their wings at the astonishing rate of 90 beats per second. Being heavy-bodied with large wings, vultures have the advantage of cruising on air currents without flapping their wings for a long time. They utilise the up-drafts generated by warm air currents.

Vulture chicks depend on spotted hyenas and such other creatures for their supply of calcium, which is necessary for the healthy development of their bones. They need pieces of bones in their food so that they can extract calcium from it, but unfortunately the meat regurgitated by their parents has little calcium. In such a situation parents depend on hyenas who with their powerful teeth and jaws can break up even the most toughest of bones. Hyenas ignore very small fragments which are taken up by these birds for their young.