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

[simple]

there are quite a few hedges managed under Environmental Stewardship Schemes - however this on its own (and thats often the case) will not save House / Tree Sparrows. Also there are quite a few hedges that aren't there anymore or are beyond remedy (apart from re-establishment)

 

[King Edward]

But agriculture is not being ignored - it's every other possible explanation of bird declines other than agriculture that is being ignored. There is a mountain of research on the effects of agriculture on bird populations, and billions has been spent on implementing their findings in the form of agri-environment schemes. Yet the Farmland Bird Indicator continues to flatline. Does that not raise a smidgeon of doubt in your mind?

£ spent does not equal habitat quality. Just because tens of thousands of farms may be enrolled in agri-environment schemes, it doesn't mean that all that farmland suddenly becomes top quality habitat (for birds or anything else) and it doesn't mean that the changes associated with agricultural intensification are cancelled out. For instance, when was the last time Britain had a major vole plague? Don't tell me the Buzzards have eaten them all.

 

[CPBell]

Simple, King Edward

I'd like to know a lot more about the Hope Farm project, and perhaps some of the correspondents here can help me.

First of all it strikes me as a bit of a no-brainer to choose a farm in the middle of the Cambridgeshire prairie, which is probably the most denuded and intensive of all intensively farmed landscapes, on which to demonstrate a result from the introduction of wildlife-friendly management.

Second, we know that intensive management for wildlife of small areas can produce results, which is of course the RSPB's stock in trade, but this can't necessarily be translated to the national scale in an economically viable way. Don't entry-level schemes represent a failed attempt to do the latter?

Third, local improvements in bird numbers resulting from 'de-intensification' doesn't necessarily mean that intensification was responsible for declines at a national scale.

Fourth, why are farmers so reluctant to follow if Hope Farm is so profitable, and why does the RSPB say that it 'relies on regular gift donations'.

Also, if anyone can point me in the direction of up to date census figures for the farm broken down by species, I would be grateful. I can only find figures up to 2004

Thanks.

http://www.youtube.com/CultoftheAmateur
http://www.cpbell.co.uk

 

[deboo]

I'd like to know a lot more about the Hope Farm project, and perhaps some of the correspondents here can help me.

First of all it strikes me as a bit of a no-brainer to choose a farm in the middle of the Cambridgeshire prairie, which is probably the most denuded and intensive of all intensively farmed landscapes, on which to demonstrate a result from the introduction of wildlife-friendly management.

I'll try and help.

Surely by being 'the most denuded and intensively farmed' just shows what could be achieved throughout the remaining British countryside?
Do you actually know where Hope Farm is in the Cambridgeshire prairie? Try Google maps. Betcha it ain't where you hoped it would be.

Then again...you've an agenda and BF is one place where you can air your views. Fair play.

dave...

 

[Motmot]

Thanks for the invitation - I'd love to galivant around Spain looking for Sparrowhawks, but I doubt whether anyone will pay for it. Failing that I think I'm still looking for my well documented exception.

Exception? To what? Don't tell me you know what's happening to the sparrow populations in every city/country in the world. Nobody knows yet, even 'scientists'.
Your theory sounds well documented though, keep trying while you get paid...

 

[Jos Stratford]

Thanks for the invitation - I'd love to galivant around Spain looking for Sparrowhawks, but I doubt whether anyone will pay for it. Failing that I think I'm still looking for my well documented exception.

No, you are not looking for it - you've been provided examples where sparrows are still common despite Sparrowhawks, you've been provided with example where sparrows are declining without sparrowhawks.

 

[King Edward]

Third, local improvements in bird numbers resulting from 'de-intensification' doesn't necessarily mean that intensification was responsible for declines at a national scale.

This misses the point I was trying to make. Hypothetically, if Sparrow decline requires both (A) intensive agriculture + (B) intensive predation by Sparrowhawks, then you can't say that either (A) or (B) alone causes the decline. Predation might appear to be solely responsible, but only because intensification had already taken place. Reversing the decline could then be done by counteracting either (A) or (B).

E.g. (hypothetical scenario) intensive agriculture results in lower food availability and reduced cover, but the population remains high because the sparrows can spend lots of time feeding safely out in the open, free from predation. Then Sparrowhawks arrive and (i) eat lots of sparrows due to lack of cover and (ii) disrupt feeding opportunities for the survivors, causing decreased survival and breeding. De-intensification (e.g. Hope Farm) could reverse this effect by providing more cover and more/better food, allowing the sparrows to spend feed more safely and more quickly.

 

[CPBell]

I've posted a video response to some of the above posts, but not the latest King Edward post which I'll respond to here.

The point I'm making is that improvements under stewardship schemes are often presented, overtly or tacitly, as evidence that agricultural intensification caused declines, partly because actual evidence is so thin. It can't explain urban sparrow declines, and rural House Sparrows in eastern England were actually increasing up to the mid-1980s right through the period of maximum intensification in the most intensively farmed part of the country, only to drop like a stone as soon as Sparrowhawks flooded back in from the late 1980s onwards.

This is what strikes such fear into the soul of the BTO, since they thought they had a killer bit of evidence about agricultural intensification in the relatively severe declines of a range of bird species in arable areas in eastern England. However this is where sparrowhawks were wiped out by pesticides and then returned suddenly several decades later to cut a swathe through naive bird populations that had never seen a sparrowhawk.

 

[Jos Stratford]

I've posted a video response to some of the above posts.

I've posted a response there.

I've posted a video response.

I recommend you take a look at the powerpoint presentation on my Youtube channel.

Moderators, is it normal for a Bird Forum discussion to be conducted half on Bird Forum and half on YouTube?

If this contributor wishes to use Bird Forum to air his views, then surely when BF members ask questions, he should post his replies here on this forum too, not repeatedly making readers leave the site to view answers elsewhere.

 

[Brian Stone]

I'd also request that responses are places here. For various reasons I often can't access video (and would prefer not to anyway) so while following this debate I am missing one side.

The language in post 228 seems to have slipped from the scientific into the somewhat emotive: "strikes fear into the soul of the BTO"; "cut a swathe through naive [sic] bird populations". I don't think it's likely to help.

 

[spencer f]

This misses the point I was trying to make. Hypothetically, if Sparrow decline requires both (A) intensive agriculture + (B) intensive predation by Sparrowhawks, then you can't say that either (A) or (B) alone causes the decline. Predation might appear to be solely responsible, but only because intensification had already taken place. Reversing the decline could then be done by counteracting either (A) or (B).

E.g. (hypothetical scenario) intensive agriculture results in lower food availability and reduced cover, but the population remains high because the sparrows can spend lots of time feeding safely out in the open, free from predation. Then Sparrowhawks arrive and (i) eat lots of sparrows due to lack of cover and (ii) disrupt feeding opportunities for the survivors, causing decreased survival and breeding. De-intensification (e.g. Hope Farm) could reverse this effect by providing more cover and more/better food, allowing the sparrows to spend feed more safely and more quickly.

This is simular to the point I have tried to make, Sparrowhawks and other predators just take advantage of an environmental change that favours them.

All I know is this, a sparrow will find little to eat and no protecttion on an expance of brick, tarmac or concrete. Over the last 10 years vast numbers of front gardens and hedges have disappeared, when you walk down an urban street, where are the sparrows? Answer, IN THE HEDGES or outside their nest site.
CPbell has said that sparrows should be able to find enough food from human waste and liitter on the streets. Not so, to access this they have to compete
with crows, magpies, pigeons, starlings, cats and rats, NO CHANCE. And besides all of the above apart from the odd exception can rear their young on purely vegetable matter. But as demonstrated by the leicster study, sparrow broods suffer considerably without invertibrate food.

 

[spencer f]

House Sparrows rely on humean habbitation and stay loyal to a particular nest site, so if Sparrowhawks nest nearby I would say Sparrows are unlikely to re-locate and thus become a sitting target.

In the pressence of Sparrowhawks it has been shown that Sparrows and other songbirds maintain a lower bodymass percentage in order to evade capture. So if their diet is not of high quality(eg large quantities of bread) there is great risk of weakness starvation.

BTO, Leiscter, Oxford and other studies have associated large densities of Sparrows with high densities of bushes, especialy native. I believe that this as many others do is because they provide protection and an invertibrate food source. So greening up a park several hundred metres away wont matter if the imediate area around the nest site is devoid of bushes.

Leicster study showed that summer broods that relied on vegetable food mainly failed. The Leicster study was judged by Summersmith who is the most well known and respected Sparrow expert in the world, I doubt that he has political ties with the RSPB.

Sparrows in the countryside have been shown to be slightly larger than their city dwelling counterparts suggesting a poorer diet (invertibrates prehaps).

Sparrows have been shown to rarely travel more than 1.5km from their nest site, so interaction with other viable colonies may be difficult. This could cause an interbreeding problem that may lead to genetic weakness.

Many people say that predators only take geneticaly weaker birds or a 'Doomed Surplus', I have to say that with the amount of predators a Sparrow has, they would have to be a genetic superstar to survive, its a wonder there are any sparrows at all.

Maybe cover was not necessary when hawks were not around but now it is. Either way it is the disappearance of woody vegetation in close proximity to properties that would be the major cause for the decline.

And let us not forget about nest sites. It cannot be denied that thousands of people have inadvertantly sparrowproofed their homes, and don't say they can go and nest in bushes, they have all been ripped out.

 

[mjh73]

Finding this thread amusing reading
C P Bell has produced a convincing theory, based on analysis of data.
It's just a theory, not a fact until someone proves it.
Similarly while there might be flaws in his methodology the theory stands until someone proves the flaws invalidate the theory (which I don't think anyone has managed to do convincingly yet) or proves C P Bell is wrong. Scientifically.
Throwing up 'the hedgerows did it' or 'the farmers did it' isn't going anywhere.
Other than providing a bit of a soap opera watching people getting increasing frustrated at C P Bell batting away the alternate arguments.

 

[deboo]

Other than providing a bit of a soap opera watching people getting increasing frustrated at C P Bell batting away the alternate arguments.

Of course he's right. Sparrowhawks hawk Sparrows. It's in the name we gave them, obviously. Just like Black-headed Gulls have got Black heads, Common Cranes are common and Water Birds are made of water.
Just a pity the Independent hasn't coughed up the £5000 prize it surely owes to CP Bell for explaining where all the spadgers have gone from our Towns and Cities. The Sparrowhawks ate them all up :eek!: Bad form.

dave...

 

[CPBell]

In the pressence of Sparrowhawks it has been shown that Sparrows and other songbirds maintain a lower bodymass percentage in order to evade capture. So if their diet is not of high quality(eg large quantities of bread) there is great risk of weakness starvation.

Good summary. I guess the above quote refers to Ross MacLeod’s paper on mass-dependent predation risk. I would urge everyone following this thread to read it – it’s freely available on the web and it’s not too technical, so pretty easy to understand.

He compared House Sparrow with a range of other songbirds that are not declining in order to test the hypothesis that Sparrows declines are caused by food shortage. This hypothesis predicts that sparrows should carry greater weight in winter, and gain weight earlier in the morning to compensate for their greater risk of starvation compared to the non-declining species. What they found was the exact opposite. Sparrows gained less weight in winter than the other species, and also put on the least weight early in the day.

He also compared weight gain in sparrow populations on islands with (Orkneys, Isle of Man) and without (Scillies, Hebrides) Sparrowhawks. On the islands without Sparrowhawks, sparrows carried about 1.5g more weight than on the islands with Sparrowhawks. The conclusion is that sparrows are not putting on weight when Sparrowhawks are present because it makes them more vulnerable to predation, but at the cost of increased starvation risk. The other species do not respond in the same way, and therefore have not declined, because they are at lower risk of Sparrowhawk predation.

Sparrow mortality may therefore have increased and caused a population decline either because of a reduction in food availability at constant predation risk, and increase in predation at constant starvation risk, or both a reduction in predation risk and an increase in starvation risk. However, we know that Sparrowhawks quadrupled over the period of House Sparrow decline, and we now know that the timing of sparrow decline across Britain coincides precisely with the appearance of Sparrowhawks in any given locality, so there’s no need to go on positing any change in starvation risk.

Unless you’re trying to hide a multi-billion pound cock-up that is.

 

[deboo]

Ok, I shall not play the arse tonight. I shall attempt to be the observant Amateur instead.
In my limited time of birding, I've witnessed 4 Sparrowhawk kills. 2 were Collared Doves, 1 a male Blackbird and 1 Blue Tit. I guess this might not be representative, but it's just what I've witnessed over 25 years. Could I have been in the wrong place at the wrong time? All were in areas where House Sparrows were quite common place.
As I've mentioned before, the number of Sparrows have been increasing in my neighbourhood in the 11 years I've lived here. I noticed few when we moved in, but in the subsequent years the population has grown - judging by the numbers on our seed feeders and the numbers of males declaring their territory/property from the roof gutters during Spring. There has been (possibly) a pair of Sparrowhawks patrolling the area for at least 5 years. I hear the warning calls of 'predator about' from birds quite frequently.
What I have noted recently tho', were that no Sparrows were advertising from the houses that have had new UPVC facias and soffits fitted. Cos the birds could not gain access to the roof spaces they required for nesting/roosting. It seems like a winning sales point, according to what I have learned from the visiting salesfolk. I have no intention of taking up their offers
So the Sparrows are now competing and quite often losing to the more aggressive Starlings that seemed to have first dibs on the 'better' roof space openings. The Sparrows were even attempting to take over the House Martins' nests!
That's just my observations from a street in rural(ish) Cambs.
I believe the decline in Sparrows has as much to do with the lack of suitable places to breed/feed/hide/roost, the increase in human generated pollution affecting the environment and food availability, more cats and of course other predators such as Sparrowhawks. But hey, I'm just an amateur observer reporting what I see.
If you wish to ignore my observations then that's your prerogative. But they are not imagined or with hoped for conclusions/results. It's just what I've seen and comprehended.

Fair play to dave I reckon...

 

[spencer f]

Finding this thread amusing reading
C P Bell has produced a convincing theory, based on analysis of data.
It's just a theory, not a fact until someone proves it.
Similarly while there might be flaws in his methodology the theory stands until someone proves the flaws invalidate the theory (which I don't think anyone has managed to do convincingly yet) or proves C P Bell is wrong. Scientifically.
Throwing up 'the hedgerows did it' or 'the farmers did it' isn't going anywhere.
Other than providing a bit of a soap opera watching people getting increasing frustrated at C P Bell batting away the alternate arguments.

You know what sadens me, when people wipe out their front gardens for the sake of fasion, functionality, or just to keep up with the Joneses. More and more we push nature away, surrounding ourselves in concrete and steel. Science is the new religion, we believe that we can't make a rational choice without its aproval. At the end of the day we are animals, and we need close interaction with plants and annimals more than you realise. I've seen so many people rip out their entire front gerden, only to cover it in brick so they can park their polluting little steel coffins on it. The result is a lifeless, characterless, sterile mass of nothing. Is this where our society is going? If so then I don't hold out much hope for our future. I see expanses of blockpaving with no life on it, then glance at an old couples shrubbery teaming with sparrows. I don't need science with all its facts and figures to convince me of what I see with my own eyes. Thats whats called common sense and visual reasoning.

 

[Andrew Rowlands]

What I have noted recently tho', were that no Sparrows were advertising from the houses that have had new UPVC facias and soffits fitted. Cos the birds could not gain access to the roof spaces they required for nesting/roosting. It seems like a winning sales point, according to what I have learned from the visiting salesfolk. I have no intention of taking up their offers
So the Sparrows are now competing and quite often losing to the more aggressive Starlings that seemed to have first dibs on the 'better' roof space openings. The Sparrows were even attempting to take over the House Martins' nests!
That's just my observations from a street in rural(ish) Cambs.
I believe the decline in Sparrows has as much to do with the lack of suitable places to breed/feed/hide/roost, the increase in human generated pollution affecting the environment and food availability, more cats and of course other predators such as Sparrowhawks.

Just about backs up my obs over a similar period in SE Wales - I blame Thatcher.

 

[King Edward]

CPBell,
I am not trying to dispute your basic finding; that the sparrow decline has been closely associated with Sparrowhawk predation. The question of interest is the interacting effect of agricultural intensification. In your latest post, for example, you raise the issue of weight and starvation in the presence/absence of predators. Surely it follows from this that, if predation risk means that sparrows must stay lighter in winter, a regular and sufficient food supply is important for their survival. They'll starve not just because they're lighter, but because they can't find enough to eat at critical times (and have to spend more time foraging in dangerous environments, exposing themselves to greater predation risk).

 

[deboo]

Just about backs up my obs over a similar period in SE Wales - I blame Thatcher.

Thank you Andy

We really should go a birding next time I'm down your neck of the woods.
As for this new religion of scientists having all the answers, well they'd be more convincing to me if they'd listen to what Joe Public observes and offers up for consideration. But hey what do we know...we're only out and about seeing stuff.

and yes I blame thatcher too...she unleashed the massive phalanx of Sprawks to swarm all over our lowland scene gobbling up all the spadgers

Down pokey quaint streets in Cambridge
Cycles our distant spastic heritage
It's a gay red roundhead, army career, grim head
If we was smart we'd emigrate

dave...