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Vanishing birds Question - Peter Jackson September 2001
Vanishing birds Question
What happened to the sparrows in London? There used to be millions. Now I see
maybe two a year. Did cats eat them all?
Answer
Estimates suggest the number of house sparrows in Britain fell between 1972 and
1996 by 9.6 million birds from a total of around 17 million. While the cause is
unknown, the best theories suggest the demise of the urban sparrow is either due
to lack of food or the wrong sort of pollution. Food sources in cities may be
declining or it may be that sparrows are losing out to other species in
competition for food. Differences in the levels and types of
pollution--including the introduction of unleaded petrol--may also have had an
effect.
One other factor may be a lack of suitable nesting sites in modern towns and
cities. Modern houses are simply not sparrow-friendly, because they lack the
holes, nooks and crannies that make for good nesting positions.
The Royal Society for the Protection of Birds is currently backing research
which it hopes will provide the explanation. This is running alongside a survey
using reports from the public, which the RSPB is conducting in conjunction with
the BBC, to determine actual numbers of sparrows and nests in urban areas.
Rural sparrow numbers have also declined in recent years but the reasons behind
this seem easier to pinpoint. Modern farming methods have reduced the number of
weed seeds on which rural sparrows feed and this, along with a decline in
insects thanks to more effective esticides, has led to a vast reduction in
countryside sparrows. This mirrors a reduction in around 20 small rural bird
species, some of which have declined by up to 90 per cent. Sparrow populations
can be supported by providing regular supplies of weed seeds. Supplies of seeds
suitable for birds can be obtained in supermarkets.
Mike Everett, RSPB, Sandy, Bedfordshire
Answer
Although we do not know why the house sparrow has declined so dramatically in
London, it is probably connected with a decline in the population of
invertebrates that are essential for the nestlings in their first few days of
life. The decline began in the late 1980s around the same time that that
unleaded petrol containing methyl tertiary-butyl ether was introduced. An impact
on the invertebrate population is possible but not proven.
The decline in urban sparrows is not confined to London. It has also occurred in
other large cities in Europe, though not in small towns where traffic density is
lower. Interestingly, the decline appears smaller in Paris where there is a
proportionately higher use of diesel fuel.
J. Denis Summers-Smith , British Trust for Ornithology Thetford, Norfolk
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