Sunday, May 14, 2000		Nature

Flying wonders
By Nutan Shukla

MOST animals must live out their lives with an ever-present threat of attack from predators. When active, they must always be on the alert, ready to avoid attack. They have three basic strategies: to freeze, to flee and to fight, often in that order. If freezing fails to work then the next step is to flee to which several refinements have been evolved by different species. Some wingless animals have mastered the stunt of gliding swiftly through the air to escape from predators and also to make foraging easier. Such animals include some snakes, lizards, opossums, frogs and colugos, even some fish.

Perched precariously upon a branch, the Costa Rican flying frog shoots out its powerful back legs and takes off into the air. By spreading its limbs wide, shaping its body like an upturned saucer, and stretching the webbed skin between its elongated fingers and toes to form four parachutes, it is able to glide up to 50 yards to the next tree. This skill enables the frog to escape predators when pursued and enlarge its feeding range without having to descend from one tree, cross the forest floor, then laboriously climb the next tree.

Flying snakes climb up rough bark in search of their prey — mostly lizards — by gripping the surface with the broad scales on the underside of their bodies. When a snake wants to change trees, it speeds along a branch and launches itself into the air.

As it begins to fall, the snake shapes its rounded body into a channel, like an upside-down water gutter, and then undulates it in a series of S-shaped coils. It can glide in this way though without much control. But by wriggling, it can change its flight path sufficiently to land close to its target.

Amongst the lizards preyed upon by the tree snakes are geckos. One of them, the flying gecko, also glides — not only to escape snakes but to hunt its own prey. The gecko glides using a skirt of skin that runs along each side of its body and by spreading its large, webbed toes.

Lizards of another group, the flying dragons, each have a fold of skin stretched across movable and much-elongated ribs. This opens like a fan and gives a flying dragon much greater control over its glide.

The art of being airborne also allows some mammals to extend their feeding range and avoid hunters on the ground. Marsupial gliders, or flying opossums, for example, glide from branch to branch in the open forests of northern Australia and New Guinea to feed upon fruits, leaves, blossoms and insects. There are several species, such as the lesser and greater gliding opossums, the largest of which is about 20 inches long, with a tail of about the same size.

As it glides with legs outspread, a marsupial glider looks rather like a rectangular kite, with a thin, furred membrance on each side of its body stretching from front to back legs. Using its tapered, furry tail as a rudder, a glider can cover up to 100 yards at a time. Larger opossums, because of their weight, tend to fall steeply with little control, but smaller species can manoeuvre to avoid obstacles.

At the end of its glide, the animal swoops upwards to a tree trunk, landing there with an audible plop. But to prevent bouncing back on impact, it hangs on tight with the extra-large claws on its fourth and fifth toes.

Often incorrectly called a flying lemur, the colugo of Malaysia and the Philippines also glides by means of furred membranes on each side of its body, but they stretch from its neck to its front toe tips then continue to the tip of its tail. Colugo glides average more than 120 yards, and one was seen to glide 150 yards and lose no more than 40 ft in altitude.

Cat-sized colugos feed at night. It is due to their nocturnal habits and limur-like heads that they are called flying lemurs. In fact, their closest relatives are probably hedgehogs and shrews.

With a hungry hunter in hot pursuit, a flying fish surges to the sea surface with its side fins folded flat against its body at a speed of 15-20mph. As the fish rockets out of the water, it spreads its large side fins to give it lift and, beating its tail vigorously, sculls across the surface. Once it has built up enough speed, the fish takes to the air, maybe spreading its pelvic fins as well, and glides at a height of 4-5 ft above the water, at speeds up to 40 mph. After 300 yards at most, it loses speed and glides down to the surface before rising in another leap.

Long, thin needlefish, which are sharp-beaked, fast-swimming relatives of flying fish, also take to the air to avoid pursuers, breaking the surface at tremendous speeds and shooting 16 ft into the air like tiny jevelins to cover distances of upto 25 yards. Flying gurnards, which are not related to flying fish, are bottom-dwelling fish that are also able to leap out of the water for short distances.