http://news.bbc.co.uk/2/hi/science/nature/5017346.stm
Migrating birds suffer huge loss
By Rebecca Morelle
BBC News science reporter
Thursday, 25 May 2006, 23:09 GMT 00:09 UK
Migratory birds have suffered a dramatic decline in numbers, according
to a study.
Species that migrate thousands of miles from Africa to the UK have been
the worst hit over the last 30 years.
The researchers say the cause of the decline remains a "mystery", but
could be linked to climate change, habitat destruction or pesticide use.
Writing in the journal Biological Conservation, they warn the losses
may indicate wider environmental damage.
The Royal Society for the Protection of Birds (RSPB) and BirdLife
International study analysed population trends of European breeding
birds, including non-migratory birds and those that migrate both short
and long distances.
The data spanned three decades, from 1970 to 2000.
"We found that long distant migrants - the ones that go right across
the Sahara, like the swallows, flycatchers and warblers - have shown a
fairly consistent pattern of decline," said Dr Paul Donald, an author
on the paper from the RSPB.
Those that winter in Africa, he said, seem to be the most affected.
The study also compared the long-distant migratory birds with closely
related non-migratory birds, but again found in almost every case that
the migratory birds faired worse.
Fifty-four percent of the 121 long-distant migratory birds studied
suffered plummeting numbers or had even become extinct since 1970.
The roll-call of declining species is long.
"Some fairly iconic species have declined enormously in Europe. There
is a very beautiful blue and purple bird called the roller - the
population of that bird is crashing all over Eastern Europe," Dr Donald
told the BBC News website.
"In the UK, other species that have declined enormously are spotted
flycatchers, pied flycatchers, wheatears, wood warblers and tree
pipits."
Changing climate
The exact reason for the birds' decline, according to the authors, is a
"mystery". But several theories to explain the losses have been put
forward, and will now be investigated.
One explanation is tied to the changing conditions in Africa, where the
birds winter.
"We know that agriculture has spread; we know there has been a
long-term drought in the Sahel; and we know huge amounts of pesticides
are used to control locust outbreaks," said Dr Donald.
The swelling size of the Sahara may also be hampering the birds.
Migrating birds face longer and longer non-stop flights across the
desert.
Climate change has been highlighted as a potential culprit. Warmer
springs in Europe are causing some insects to hatch earlier in the
year, which means by the time the migratory birds arrive to breed and
raise their young they may have missed their much-needed food-source.
"Migrants make up a high proportion of our species of birds, so this is
a big conservation issue," said Dr Donald.
"But if you think that these are birds that cover vast areas of the
Earth's land-surface - this consistent pattern of decline is indicative
that there are some pretty severe environmental changes going on
somewhere which might also have an impact on humans."
The authors conclude that urgent action is needed to uncover the cause
of the decline.
"There is something about being a migrant that counts against them,"
said Dr Donald.
"These birds have been slipping away from under our noses for 30 years,
and we've never has really noticed it before."
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