"martin" wrote in message
...
On Sun, 21 Aug 2005 13:23:20 +0100, Jaques d'Alltrades
wrote:

The message
from martin contains these words:

.... how many sparrow hawks does it take to eat millions of sparrows
per year??

Divide 'millions' by (say) 10 × 7 × 52 and you might be surprised at the
result.

To save you the trouble, somewhere near 275 sparrowhawks per million
sparrows, assuming that one sparrowhawk will kill (and not necessarily
eat all of) ten sparrows per day.

Oh, and I didn't see the OP (probably crossposted), but the songthrushe
population is *NOT* declining, it is growing quite markedly.

http://www.garden-birds.co.uk/birds/housesparrow.htm
The House Sparrow is a Red List species owing to a serious decline
(over 60%) in its population over the last 20 to 30 years. The reason
for the decline is not known, though several theories have been
suggested:

* methyl tertiary butyl ether (MTBE) in unleaded petrol is
affecting abundance of insect for feeding young.
* autumn sown cereal crops leaves little stubble for them to
forage in or spilt grain to glean.
* predation by the increasing number of cats.
* modern buildings have fewer holes and crevices where the birds
can nest.
* Collared Doves compete for a greater share of the same food
types as the sparrows.

--
Martin

how come a doubling of the sparrow hawk population over the same period isnt
mentioned as a potential contributory factor?
http://www.bto.org/birdtrends2004/wcrsparr.htm

or wouldnt that lead to any interesting & grant-funded research?

--
Tumbleweed

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