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Global warming changes birds' direction

2001-12-03 11:38

Hamburg - Global warming is changing the migration patterns of many birds, altering flight paths that have remained unchanged for generations and that were firmly anchored in their genes, scientists say.

"Warming in Europe has probably changed the migration direction of the warbler," said behavioural researcher Eberhard Curio of Bochum University in western Germany, Ruhr region.

The small birds native to central and eastern Europe used to migrate southwest to spend winter in southern France, Spain and northern Africa. But now Curio says many of them fly westwards to spend the colder months in southern England.

"Such changes in migration patterns are the result of natural selection. The birds that fly in a disadvantageous direction will die," the biologist said. Yet the birds that fly to more favourable destinations pass on this behaviour pattern to their offspring.

Researchers currently believe that birds use a kind of second sense to orient their migration patterns, either a visual orientation based on the position of the sun, or with the aid of a sort of inner compass. Since animals possess a precise inner clock, they can determine their position by the sun and the stars, said Curio.

Navigation by inner compass, relies on the Earth, magnetic fields.

The routes taken by different species of birds are very much influenced by their flight capabilities. Swifts, some birds of prey and storks need up currents to fly. This means they favour overland flight paths southwards rather than long trips over the sea. This also gives the birds the chance to stop on the way to gather their strength.

"Many migratory birds need rest stops at regular intervals to refuel their fat reserves," said bird expert Franz Bairlein of the Institute for Bird Research in Wilhelmshaven, northern Germany.

"The garden warbler doubles its weight before its strenuous flight over the Sahara to its winter quarters in southern Africa,"he said.

Yet sea swallows are world masters in long distance flights. They begin their 15 000-kilometre journey southwards in August and reach their winter quarters in December.

Many species, such as the house sparrow, blackbird, swan or kestrel, do not migrate. "These birds can remain here because they have been able to adapt their nutrition to the unfavourable climate, said Curio. Great tits that feed on insects during warmer seasons will also eat beechnuts or other seeds in winter.

"Blackbirds eat different foods throughout the year, including worms, insects and fruits, but in winter they also eat other berries."

Curio recommends that people feed these birds in winter. "It is important to keep bird tables meticulously clean, otherwise the birds could succumb to diseases such as salmonella," he said.

Birdhouses also help children learn about nature, he added. "So that children can still name different species of birds, not just different types of cars." - DPA

- SAPA

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