Sunday, February 17, 2002		Nature

Led by their noses!
Nutan Shukla

IN the avian world, very few creatures have the sense of smell and New World vultures are among those few proud possessors of this rare quality. The ability to smell offers them the opportunity to find food even in the dense forests of South America. Fresh corpses tend to go unnoticed for they have no strong smell, but a carcass a day old or more can be easily located.

Asiatic vultures or the Old World vultures are devoid of the sense of smell, they are unable to find a carrion if it is covered even with a sheet of paper or cloth, while their American cousin, specially turkey vulture, solves this problem without any difficulty. They fly low to sniff out food or else perch on a tree nosing out the dead flesh with the help of their large nerve-rich nasal organs that heighten their sense of smell.

Decaying flesh releases some gases, which rise up in the sky and guide these birds to the food source. They gather above up-currents of the chemical ethyl mercaptan coming out from hidden sites in canyons, and thus are able to find the hidden corpses. Their powerful sense of smell has also enabled them to exploit forest habitat where they cannot see through the canopy of trees. Many species of vultures keep a close watch over these birds and follow them to get their share of food.

There is one incident, which also proves that turkey vultures rely more on their sense of smell. At a place in North America some engineers were working to plug the leak in a gas pipeline, but were unable to locate the spot of leakage. Meanwhile, one of the engineers saw some vultures congregating at a particular spot, when they went there to find out the reason they noticed that the birds were attracted by the leaking gas. This simple observation not only saved them time and money, but also proved that the birds rely on their noses rather than their eyes.

Although, known by the same name ‘vulture’, New World vultures are, in fact, more closely related to storks rather than birds of prey. Scavengers by nature, they perform the same job in Americas as the other vultures do in the Old World.

In many places it has been observed that turkey vultures have discovered an easy way of obtaining food by harassing great blue herons. The very young chicks fall prey to these large birds while the older ones defend themselves by regurgitating food and spitting it at their tormentors. For vultures it is the best way to obtain a partially digested meal, specially, for their own chicks that cannot digest absolutely raw or stale meat.

Another species of New World vultures, the large king vultures, perform the same task the lappet-faced does in the Old World, tearing and devouring skin, tendons and other coarse tissues with their powerful beaks, thus making an opening for other species to reach softer tissues.

Condors are birds that belong to the same family as that of New World vultures. They are not only large birds of prey, but also one of the largest flying birds in the world. There are two species of condors, one found in the Andes Mountains of South America and the other living in California. feeding on carrion, condors lay their eggs in caves or in holes.

Cruising on air currents Andean condors can travel up to 110km without flapping their wings, the longest distance any bird can travel like this. They utilise the up-drafts generated by warm air currents to keep themselves aloft. At high elevations, where these birds are found, wind is a considerable problem, adding to the chilling effect of the cold. It restricts flight in all but the strongest of fliers. One such is Andean condor that soars on the wind currents over the entire length of the Andes with ease.

Inhabitant of South America the bird is the largest and the heaviest of all raptors with a weight of about 13.5 kg. Feeding on carrion, it can eat considerable amount of meat in one go. As far as the greatest wingspan of any land bird is concerned, Andean condor and marabou stork, another carrion eater of Africa, are the two claimant of this distinction. Both species have wingspan of about 11ft. They have long, broad wings with fingered primaries best suited for soaring flight.

California condor is one of the rarest bird with hardly two-three left in the wild. Weighing about 8 to 10kg with a wingspan of about 3 metres it is North America’s largest flying landbird.