In article ,
Malcolm wrote:
"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.)
Well, I will swallow the first as a very likely cause of the decline
from 1925 to 1948. The latter is pretty dubious, because there are
still a lot of older buildings around, sparrows aren't all that fussy
and smaller numbers need fewer places. c.1985, we had some nesting
behind the guttering in a (then) new extension. It is almost certainly
a cause for some birds, but sparrows?
Yes, and you have admitted that there are smaller numbers. And although
there are *some* old buildings around, they are not nearly as common,
nor widely distributed, as they once were.
In most of the south-east, there are enough to provide for a sparrow
population of 10 times that of 1975, probably 100 times and possibly
1,000 times. As I said, they will nest behind guttering where there
is a suitable board to start building - and there are a LOT of such
places, even on modern houses. While they LIKED thatch, they were
not dependent on it, and the practice of wiring thatch was near-
universal well before 1975.
The decline in farmland also dates to earlier than 1970, with the
widespread introduction of tractors in place of horses and all that
meant over the next decades in terms of cleaner arable fields, loss of
hedgerows, more rapid ploughing, etc., etc.
And there has been very little change since 1975 over most of the
south-east,
Have you figures to back that assertion? The pattern of cropping in the
south-east will surely have changed in the last thirty years as it has
elsewhere with, to give just one example, autumn stubbles being ploughed
immediately after the harvest instead of left through the winter.
I have the evidence of my observation, from having lived in the area
over that period, having been interested in such things, and having
watched the changes. Have YOU any evidence of a change large enough
to account of a population reduction of over 10 times?
Please don't quote winter wheat figures for the UK as a whole, because
it was near-universal in the south east a long time before it was
across some other parts of the country.
certainly not enough to account for a tenfold reduction
(unless you bring in the passenger pigeon effect, which is not
intrinsically impossible, but is a bit implausible).
I wasn't bringing in the passenger pigeon effect, I was relying on good
evidence that there has been a tenfold reduction.
I never said there hadn't been - I have posted in the past that I have
observed it, too. I am casting doubts on your statement of possible
causes, which strike me as uninformed and implausible speculation.
If you disagree, please provide at least some reasons to back them
up, and preferably evidence.
My hypothesis is that many declines have been due to cats - and I
don't mean feral ones. If you consider the proportion of the south
east that (a) has vegetation and (b) is outside the territory of
any cats, it HAS decreased by tenfold or more since 1966. Whether
this is the cause for sparrows, I can't say.
I know there is a modern estimate for the number of cats, at 7-9
million, but has there been a significant increase in the last 30 years
and sufficient to account of declines in birds?
In much of the south-east, yes. It isn't the NUMBERS, but the fact
that infilling and the conversion of other buildings to houses has
meant that the area outside the territory of at least one cat has
almost vanished. That was not so even in 1966.
What we need is some larger predators, both to keep the deer down
(especially for birds that rely on woodland undergrowth) and to keep
the cats down. Bring back lynx. I know that you disagree,
No, you don't. When have I argued against bringing back the lynx?
http://groups-beta.google.com/group/...browse_thread/
thread/952053ed420dddaa/f30c954e3cb465db?q=lynx+(malcolm+OR+ogilvie)+
group:uk.rec.natural-history#f30c954e3cb465db
gives evidence. You have got Google to remove your postings from
the archive, so they are not present, but there is enough quoting
to show what you said.
I can't imagine the lynx, even if well established, accounting for that
many deer, though I suppose they might take some muntjac.
(a) muntjac are perhaps the main problem in the south and (b) most
populations of Eurasion lynx are said to prey on roe deer (the
other deer problem).
In article ,
Malcolm wrote:
Then you are very lucky, because there has been an even greater decline
in tree sparrows, to the point of complete disappearance in some parts
of the country, than in house sparrows. Farming changes are again
implicated at least in part.
That is, at least, plausible. They always were more dependent on
hedgerows than house sparrows, and there HAS been a change in the
management of hedgerows.
Regards,
Nick Maclaren.