Sunday, June 25, 2000		Nature

Swallow this!
By Nutan Shukla

FROM a distance, male and female swallows are virtually indistinguishable. Closer scrutiny shows that a male’s plumage is somewhat brighter, but the main difference is that a male has longer streamers on his forked tail. Although this is unlikely to give him any aerial advantage, it does have a purpose.

The length and symmetry of a male swallow’s tail reveals what a female looking for a mate needs to know about him. Growing a long tail demands a great deal of energy, and only a strong bird can afford to do it.

So females prefer mates with long tail streamers, and they are the first males to find breeding partners in spring. Swallows that breed early have enough time in summer to raise an additional brood of up to six. Consequently, long-tailed males tend to father more offspring than their shorter-tailed counterparts.

Gilbert White of Selborne (England), a country vicar and famous naturalist, who lived in the late 18th century, believed, like Aristotle, that swallows spent winters in the mud at the bottom of the ponds. The reason for such an idea was perhaps the habit of these birds gathering in reedbeds before migrating.

Now we all know that like other birds, swallows too migrate to warmer places during winters. Most of Europe’s swallows head for southern Africa to escape the harsh winters of the northern hemisphere, covering about 11,000 kms. This journey is particularly dangerous because they have to cross the vast Sahara Desert to reach their destination. The risk factor can well be understood by the fact that the chances of both the members of a pair getting there and coming back safely are only about 20 per cent. By desert crossing these birds become so highly exhausted that they do not even try to fly away when anybody picks them up.

Many of these birds take an arduous route over the Alps. Often they are overtaken by early snowstorms, and unless they find shelter, many die. High in the mountains is St Bernard’s Monastery, whose monks have for centuries cared for alpine travellers — including birds — which they shelter until they are fit enough to continue their journey. Among other havens for exhausted migrants are lighthouses and ships at sea, whose decks are sometimes covered with birds in a state of collapse.

There are about 24 species of swallows and martins which are found worldwide. They are mainly blue-black birds with many of them having white or chestnut under-parts and have been placed under genus ‘Hirundo’. They build mud nests which can be located at a variety of sites.

Barn swallow, also known as common swallow, is one of the few specialist insect catchers which takes its food in midair. According to a study, in a single day a pair of birds may make up to 425 hunting trips and catch up to 8500 insects between them. It catches several flying insects in one trip and then crushes them into a ball of food before taking them to the chicks.

In terms of zoogeographical distribution, this bird is the most widely found ‘perching bird’, found worldwide except in some remote islands and Antarctica.

White-eyed river martin, a tropical swallow found in Thailand, is highly endangered species. It was discovered in 1968 and has not been seen at all since 1980.