Scientists are struggling to
explain
a catastrophic decline in the number of birds
whose annual visits are part of
our folklore
Sunday 24 April 2011
The Observer
Robin McKie, science editor
This article appeared on p12
of the Main section section of the Observer
on
Sunday 24 April 2011.
It was published on guardian.co.uk
at 00.06 BST
on Sunday 24 April 2011
Some of Britain's most cherished spring visitors are disappearing in their
thousands. Ornithologists say species such as the cuckoo, nightingale and turtle
dove are undergoing catastrophic drops in numbers, although experts are puzzled
about the exact reasons for these declines.
The warning, from the RSPB, comes as the songs of the cuckoo, nightingale and
wood warbler herald the return of spring. In the case of the cuckoo "the
simple bird that thinks two notes a song", according to the poet William Henry
Davies its call has become synonymous with the arrival of warm weather. It is
the quintessential bird of spring.
Yet there is now a real risk that, with other migrant birds from Africa, it may
no longer make its annual appearance in our woodlands, said Dr Danaλ Sheehan, a
senior RSPB conservation scientist. The call of the cuckoo could be silenced in
the near future unless scientists can unravel the causes of the drastic decline
in their population, she said.
According to Sheehan, numbers of migrant birds from Africa have declined
dramatically in the UK since 1995. For turtle doves the figure is 71%;
nightingales, 53%; and cuckoos, 44%. "That is a very significant and very
worrying decline," she added.
"The real problem is that there are so many different possible causes for these
losses which makes it difficult to tease out the factors involved in their
decline and to prepare plans to put things right.
"These losses could be the result of changes in farmland use in Britain which
are affecting the way these birds breed when they arrive here in spring. Or they
could be due to the spread of human populations in Africa and the destruction of
natural habitats where they make their homes in winter.
"Climate change is almost certainly involved as well. Our problem is to unravel
those different causes and assess how they interact."
In a bid to explain what is happening, the RSPB and groups such as the British
Trust for Ornithology have launched a series of projects in the UK and in
Africa. These include new surveys of numbers of different species arriving in
Britain as well as studies, in Africa, of sites that provide winter homes for
these birds. Targets will include the cuckoo, nightingale and the turtle dove as
well as the wood warbler, garden warbler, whinchat, and pied flycatcher as well
as the swift another popular visitor. Its numbers have dropped 30% since 1995.
"The global pressure for land has now become extreme, and it is starting to have
real implications for long-distance migrant birds," said Andre Farrar, the
RSPB's campaigns manager. "Climate change which affects timings of breeding
cycles is another critical factor."
However, the work will be tricky thanks to the complexity of bird migration
between Africa and Britain. For a start, these visitors have their winter homes
in very different areas. Some birds, like the nightingale, cuckoo and swift,
winter in humid western regions including Nigeria and Ghana while others,
like the turtle dove and yellow wagtail, winter in the dry Sahel area in
countries such as Chad. "Both regions are affected by rising populations of
humans, but in ways that will have subtly different effects on land use and on
individual bird species," said Sheehan.
On top of changes of land use in their wintering grounds, scientists suspect
that many migrants are finding it increasingly difficult to feed themselves when
they come to breed in Britain. For example, cuckoos eat large moths and it is
known that in recent years numbers of such insects have dropped significantly in
the UK.
There is almost certainly a significant problem caused by climate change.
Migrant birds arrive and breed and then have chicks at times which are no longer
synchronised with the best periods when food, such as insects, is available.
Again this is likely to have a serious impact on population numbers.
On top of these factors, turtle doves and nightingales are affected by the loss
of sandy scrubland on which they like to breed. Intensification of farming has
seen major reductions in this sort of habitat and this has had an impact on
migrant birds, added Sheehan.
There are factors involved from outside either Africa or Britain. "Adding insult
to injury to the effects of this land use and climate change is the massive
slaughter that takes place in spring and autumn when birds, flying from and to
Africa, cross islands in the Mediterranean Sea, such as Cyprus and Malta," added
Farrar. "There they are shot, in their hundreds of thousands, by hunters who
just enjoy killing them for the 'sport'. It is against EU law, but that doesn't
stop it happening."
Migrant birds from Africa clearly face a barrage of problems, although the
effect of these will differ from species to species. The crucial point, say
ornithologists, is that some of the most welcome visitors to the United Kingdom
are now disappearing.
"Some of these birds are closely woven into our culture, like the cuckoo," added
Farrar. "Others like the spotted flycatcher, which specialises in living in
old leafy churchyards and large gardens are less well known but loved
passionately by small groups of people who are very possessive about them and
who watch out carefully for their return every year.
"And that sums up our attitude to migrant birds. We are at the northern edge of
their ranges. However, they breed here and we identify them as being British,
though it could just as easily be argued they are African or simply birds of the
wild skies. Nevertheless, we have a deep, complex relationships with these
creatures."
This point was backed by Sheehan. "These birds arrive in our countryside just as
the first good weather arrives. We associate them with spring and warmth. That
is why they appear so often in folklore. They are part of our culture which
makes the declines in their numbers so worrying. We have got to find out what is
going on as soon as possible.
"Many people will hear their first cuckoo of the year this weekend. It is not
guaranteed they will be able to do that 10 years from now."
