FOR thousands of years, Spanish storks have been migrating to African countries like Senegal and Ethiopia from Europe. Now, a third of Spain's 22,000 white storks prefer to stay back during the winters and feed on garbage s dumps. This is a radical change in their habit, says ornithologist Ezequiel Martinez. "In the last 15 years, storks have started cutting their migratory route shorter and shorter," says Martinez.

The reason for this change in behaviour lies in the urbanisation and gradual disappearance of traditional bird habitats such as forests and rivers. Now, instead of using trees, storks build their nests on church towers, telephone poles or antennas. Of the 744 nests registered in Madrid this year, 445 were built on human habitation. And the nests were made of plastic, cloth and rubber. "Garbage dumps allow the birds to eat all year, so they no longer take the trouble of migrating," says another ornithologist, Juan Carlos de Moral.

Storks are not the only birds changing their migratory habits. Even black-headed gulls are leaving their natural seaside habitat for inland dumps, according to de Moral.