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Sparrowhawks responsible for House Sparrow decline says scientist (1 Viewer)

spencer f

Well-known member
London Birder
Would you say there are adequate nesting oppertunities for sparrows( dense hedges, cavities etc) in and around the royal parks.
 

MJB

Well-known member
Nest boxes, dense hedges and fewer insecticides and Robert is indeed your Dad's brother!

Just a slight persuasive amendment to 'dense hedges', Jane: 'dense hedges with an "A" cross-section'. Everywhere I've done census or atlas work, hedges with that cross-section (narrow at the top, broad at the bottom, fewer gaps, more room for invertebrates, small mammals and reptiles), they tend to hold more birds than those trimmed vertically, whatever the season.
MJB
 

John o'Sullivan

Well-known member
Mr Bell,

I'm still interested in your mechanism. Why do sparrowhawks reduce sparrow populations so dramatically.

I have proposed a mechanism that explains sparrows vulnerability i.e. they have evolved a tendency to only fly in straight lines away from cats and are too stupid to change, whereas goldfinches hide in thistles and greenfinches hide behind feeders full of black niger seeds.

The favoured theory that others are proposing seems to be that sparrows have to learn how to hide in A shaped hedges and as long as they don't stray too far from these they are safe and their population can recover.

Why do you think sparrows are so vulnerable to sparrowhawks?

Without a mechanism we only have a correlation and it would be a shame that you lose your job over nothing more than a correlation and a refusal to listen to others explaining that this is all that it is.
 
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spencer f

Well-known member
Where urban and agricultural habbitat is degraded corvids CAN be a problem because they can adapt to almost any environmental conditions almost immediately, where some specialised songbirds can not. The answer should almost NEVER be culling but habitat enhancement and preservation.
 

pianoman

duck and diver, bobolink and weaver
Some Hyde Park / Kensington Gardens House Sparrow census figures;

Nov 1925: 2,603
Dec 1948: 885
Nov 1966: 642
Nov 1975: 544
Feb 1995: 46

I'd love to know the figures between 1995 and present. Are we absolutely sure that HOSP is still declining (leaving aside the causes)? I still get the impression that a recovery is currently under way.
 

spencer f

Well-known member
Current figures are zero I believe. Yes in birmingham suburbs there seem to be more surviving adults this year. They are starting to get excited, nearly nest building time.
 

London Birder

Well-known member
Spencer F,

I can't really add much to what Sanderson published in '95 regarding habitat loss, not much has changed since then to be honest. There certainly remain areas where sparrows could nest. Just no sparrows whatsoever.
 

London Birder

Well-known member
I'd love to know the figures between 1995 and present. Are we absolutely sure that HOSP is still declining (leaving aside the causes)? I still get the impression that a recovery is currently under way.

There appears to have been an upturn in sparrow fortunes come 1996 when an estimated total of 60 pairs bred. In 1997 there were 25-27 territories in the CBC plots but only 11 in Hyde Park in 1998 (info for adjacent Kensington Gardens for that year amounts to 'bred') and ten-11 pairs in 1999 (one nestbox was predated by Sparrowhawk and Jay). In 2000 none were recorded in the Hyde Park CBC plot but six pairs nested in Kensington Gardens producing eight broods (with four young taken by Sparrowhawks). Two pairs bred in 2001 (both in Kensington Gardens, none in Hyde Park) and there were up to seven birds at the beginning of 2002 (but males failed to find mates and none were seen after 23rd April). No definite breeding records for 2003, just singles on two dates, two on one date, and three on another. No reports between 2004 and present other than a single in 2006 and four reported in January 2010.

No recovery as yet.
 
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cates

Well-known member
Some Hyde Park / Kensington Gardens House Sparrow census figures;

Nov 1925: 2,603
Dec 1948: 885
Nov 1966: 642
Nov 1975: 544
Feb 1995: 46

'The reasons speculated for the national decline - changes in farming practices and increased number of predators, including Sparrowhawks - do not seem to apply to the parks unless the population, considered by some as largely sedentary, does require an injection of birds from outside London. The decline in horse traffic after 1925 has also been suggested as a possible factor'. (Sanderson. 1995).

My last sighting was of a single in 2006 though four birds were reported in January 2010 on one of the areas set aside for the RSPB's House Sparrow project. These areas now appear to be defunct from what I can see.

As for Sparrowhawk; a pair probably breed annually (but ascertaining this has been surprisingly difficult). Sanderson states that there wasn't a single record of this species between 1953 and 1975 (though this in part will be down to observer coverage) and only seven records between 1975 and 1995.

in central london you're only 15 miles away from intensive farming in any given direction. chemicals effect far further than where they are used in the immediate area; they perminate every living cell. both the chemicals and the sparrows are a good deal less sedentary than many realise.
 

spencer f

Well-known member
You may be right, but where is your evidence that 'chemicals' directly affect sparrow success. And if you are right why is the build up in the levels of such 'chemicals' not having an effect on the predators.
 
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Apodemus

Well-known member
The main effect that chemicals are having now is in reducing abundance and diversity of "weed species" in the countryside. Far more insidious and worrying than direct poisoning.
 

spencer f

Well-known member
I thought the change in crop timing had more to do with it, ie winter wheat and loss of field stuble as a result of late cultivation. Plus loss of decent hedgrows due to grubbing and flailing.
 

Jane Turner

Well-known member
Seems silly to argue about which specific individual change in agricultural habits was the single most important cause of declines in Farmland birds.....
 

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