"Six years ago, The Independent began highlighting the decline of our
most familiar bird. The campaign put the disappearance of the house
sparrow on the national agenda. Abundant until the early 1990s, Passer
domesticus has now gone from central London, apart from isolated
pockets, and declined in other large urban centres, such as Glasgow.
The cause is unknown. Our £5,000 prize for the first convincing
scientific explanation stands, although many theories have been put
forward, including magpies, cats, pesticides, peanuts, climate change
and home improvements. Research by Dr Kate Vincent of De Montfort
University suggests a decline in insects is leading to sparrow chicks
starving. The effect is seen in Paris and across Europe."
Interesting expression of the common misconception that there is usually one
and one only explanation for ecological phenomena.
To my mind ALL the proposed explanations the paragraph above probably
contribute to the decline of sparrows in northern and central Europe, but
the decline should be seen in a context of the recent history of the
species' distribution and abundance.
House Sparrows probably originally lived in southern or south-eastern Europe
in small colonies around good stands of native grasses, where there were
tree hollows for nesting, (probably in similar numbers to colonies of
Australian native finches presently) and spread north with the spread of
agriculture. The sparrows' heyday was in mediaeval times with extensive
grain agriculture and wide use of horses (plenty of grain around farms and
holes for nesting). In the C19 they were the commonest urban bird because of
urban stabling for horses (plenty of oats lying around in the street). In
the mid C20 they would have begun to decline from an overwhelming abundance
as horses were no longer used extenssiely for transport, but may not have
declined so abruptly because of the extensive areas of waste ground near the
centres of many European cities from war-damage, which in many cases
persisted until the 1960s.
After this sparrows will have declined slowly, their decline hastened by
tidier cities, fewer nest holes, fewer insects &c. They are now contracting
to a more realistic commensual existence, and in time may contract further,
back to their original range.
On the western slopes of NSW they seem to live around country towns and
along major roads where there are trees or buildings for them to nest in and
stands of introduced grasses (or grain silos!). This may be a more realistic
picture of their original habitat than the European urban setting.
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