Sunday, October 1, 2000		Nature

SNAKES and some lizards commonly flick their tongues in and out of their mouths. Few people know they ‘taste’ the air for evidence of food nearby. Forked-tongued reptiles, like monitor, whiptailed and beaded lizards and snakes, have a better-developed sense of smell than their broad-tongued cousins, like alligators, crocodiles and and house lizards. Chemicals on the wind are trapped on the moist tongue and pressed against the Jacobson’s organ, a pair of cavities, lined with sensory cells, in the roof of the mouth near the snout.

The gigantic, 10-foot long, Komodo dragons of the islands of Indonesia depend on their acute sense of smell to track down their prey, often wild deer, pigs and feral goats. They lie in wait, hidden in bushes or scrub, flicking their tongues in an out until the tell-tale smell of prey is near. Although large and bulky, weighing up to 165 kg, these lizards which are the world’s largest, are surprisingly agile and can hijack an unwary animal. They have even been known to follow a pregnant goat, waiting patiently until she drops her kid before they race in, grab the new-born and rip it apart as they wrestle for a morsel.

More often Komodo dragons will home in on carrion, the irresistible smell of a petrifying carcass acting as an olfactory beacon for every dragon within smelling distance. But those other consumers of dead bodies, the Old World vultures, do not use smell to find a corpse, as was once suspected; rather, they use sight. And if one spots food, the very act of dropping down to eat it attracts all the other vultures in the neighbourhood and a large, noisy, squabbling flock soon forms.

Some of the New World vultures, on the other hand, do use smell, and in doing so have been able to search for food in inaccessible places. Turkey vulture, an American cousin of Asian vultures, has a very sensitive nose. It flies low to sniff out the carrion or else perches on a tree, trying to smell dead flesh. These birds have large nerve-rich nasal organs. Decaying flesh releases some gases which rise up in the sky and help these birds to find the carrion. More closely related to storks rather than birds or prey, Turkey vultures gather above the up-currents of the chemical ethyl mercaptan coming out from hidden sites in canyons, and thus are able to find hidden food. Their powerful sense of smell has also enabled them to exploit the forest habitat. Many species of vultures keep a close watch over these bird and to get their share of food they follow them.

The expert smell-seeker of the bird-world is the New Zealand kiwi. As it evolved in the absence of predators, it is a ground-dwelling, flightless, nocturnal bird. Due to its sense of smell and giant hedgehog-like appearance, it is often described as an ‘honorary’ mammal.

While comparing the size of olfactory bulbs in the brain with the size of forebrains, it was found that the kiwis along with very few species like albatrosses, petrels and grebes, etc have the largest olfactory bulbs. Adapted for nocturnal life in which, presumably, sight is less important, kiwis are among the very few birds known to use the sense of smell for finding food. Earthworms are their favourite food and are located with the help of nostrils which are situated at the tip of the long and flexible, but slightly down-curved bill. Other long-billed birds have nostrils at the base of their bill. Kiwi thrusts its bill into the soil to smell out worms and insects. Once it locates the food it pick it up with the tip of the bill and throws it back into its throat with a quick jerk.