Malcolm wrote:
In article , ned
writes

"David" wrote in message
...


snip

House sparrow population has declined by about 50% since 1970.

.....Damned statistics!
I think that 1970 figure coincided with a peak in the sparrow
population.

What's your evidence for this? The reason the year 1970 is often
quoted in bird statistics (damned or not!) is because it was the
mid-point of the first BTO Atlas project which mapped all species
accurately for the first time, combined with an estimate of numbers.

So the current low may not be quite as dramatic as is put about.

I think it is. Here are some counts of the numbers in Kensington
Gardens, London, made by Max Nicholson:

November 1925 - 2,603
December 1948 - 885
November 1966 - 642
November 1975 - 544
February 1995 - 46

Damned statistics! It seems that the graph I was quoting from showed a
'mild' peak around that time - but did not go back much further.
However, I've just dug this out,

"Possible explanations for the decrease in House Sparrow abundance
include general reductions in food supply, reductions in the amount of
grain spilt during agricultural operations, tighter hygiene
regulations, increases in predation, and the use of toxic additives in
unleaded petrol (Crick et al. 2002). BBS data have shown increases
recently in Scotland and Wales. Following widespread declines across
Europe during the 1990s ....." ( - so its not just a UK concern.)

I can report that there seems to be no decline in tree sparrow
numbers - at least not in my back yard.

I would have thought that Kensington Gardens figures might be
significantly influenced by inner city traffic polution.

--
ned

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last update 08.03.2005