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