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

So a single site would be enough to convince you? Not even a tetrad or even a small geographic region?

Has there been any research on the affects of panel fencing on birds in the urban environment? Back in the 1970's I recall that just about every garden would have a decent (usually privet) hedge. Since the 1980's many of these have been replaced by the easy to manage panel fence. These offer A) a lack of nesting sites and B) a lack of refuge for birds when mammalian and avian predators strike.

I remember working for the RSPB and fielding a call from a very ditressed lady who had noticed an almost total lack of birds in her garden in comparison with the previous year. She stated that she had seen the farmer spraying crops in the adjacent fields and made a correlation with that. After explaining that spraying was unlikely to be the cause, I asked if she had made any changes in her garden. She replied that she hadn't. I then mentioned panel fencing and she informed me that her hedges (too high maintenance) had been replaced by said fencing.

Only conjecture on my part but I think these are a real menace.

Jane Turner said:

So a single site would be enough to convince you? Not even a tetrad or even a small geographic region?

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When I say on a site by site basis I’m referring to the analysis shown in figure 3 of the paper, where we equalise date of Sparrowhawk establishment across sites and look at the average pattern. As I’ve said time and again, many individual sites don’t show any relationship, but it’s the overall pattern that’s important, because it evens out all the quirks. The contributors who think they are shooting the conclusions down in flames because they still have Sparrows in their gardens, despite the local pair of Sparrowhawks, are therefore deluding themselves.

If you really want to understand what we did I would urge you to read the paper itself. If it’s too difficult, watch the powerpoint I put together. Ask as many questions as you like – I’m happy to answer them here. I promise I won’t hide in my ivory tower like the fine folk at the BTO and the RSPB.

peterbrash said:

Has there been any research on the affects of panel fencing on birds in the urban environment? Back in the 1970's I recall that just about every garden would have a decent (usually privet) hedge. Since the 1980's many of these have been replaced by the easy to manage panel fence. These offer A) a lack of nesting sites and B) a lack of refuge for birds when mammalian and avian predators strike.

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There has certainly been endless speculation about hedge removal, plastic fascia boards, decking, Leylandii, cavity wall insulation, off-road parking spaces etc. Every visible change in the urban environment has been cited at one time or another, but they don’t bear scrutiny. See post 265 for instance.

Nobody remembers the changes that have occurred in the other direction. I also remember the 1970s, and I recall great swathes of terraced housing with back yards rather than back gardens, and hardly a green leaf in sight, but plenty of sparrows. Most of these have been cleared and replaced by housing with way more greenery, but often without a sparrow to be seen.

So if say a whole county had records that bucked your trend, you'd ignore that?

Jane Turner said:

So if say a whole county had records that bucked your trend, you'd ignore that?

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It’s not a question of ignoring: I never ignore any information that’s available. How much store you set by it is another question. Maybe a lot if it’s good quality information and the county is, say, Yorkshire; maybe not very much if it’s poor quality and the county is Rutland. We don’t live in a world where ideas are proved and disproved in an instant, or where people wear either black or white hats.

Will you tell me which county it is if I say please?

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

Christopher,

when you say that changes in the urban environment do not bear scrutiny, do you mean that these factors have been scientifically investigated and found to be of no significance or that there is not a scientifically rigorous way of investigating these factors?

If the answer to this is that the panel fence/hedge question has been investigated I'd be interested in any links to papers.

I could imagine that restricting availability to nest sites could be a causal factor in decline and may be worthy of investigation. Correlations with Leylandii, parking spaces, unleaded petrol, mobile 'phones etc less worthy in the case of house sparrows and most other species.

CPBell said:

It’s not a question of ignoring: I never ignore any information that’s available. How much store you set by it is another question. Maybe a lot if it’s good quality information and the county is, say, Yorkshire; maybe not very much if it’s poor quality and the county is Rutland. We don’t live in a world where ideas are proved and disproved in an instant, or where people wear either black or white hats.

Will you tell me which county it is if I say please?

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

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So which of the following would convince you? Merseyside, Lancashire, Derbyshire, Cheshire, Staffordshire, Clwyd, Cumbia

peterbrash said:

when you say that changes in the urban environment do not bear scrutiny, do you mean that these factors have been scientifically investigated and found to be of no significance or that there is not a scientifically rigorous way of investigating these factors?

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I suspect there is a scientifically rigorous way of investigating the effect of hedge replacement, but if so it hasn’t yet been followed. One possibility would be to send out questionnaires to all participants in the Garden Bird Feeding Survey to ask if and when they’ve had hedges replaced by walling or fencing some time since 1970, since the theory would predict a temporal correlation with Sparrow decline across sites. I’ve no doubt that if a pattern similar to that in figure 3 of our paper emerged from such an analysis, nobody would be tying themselves in knots trying to explain it away.

What there have been instead are surveys of sparrow distribution in relation to aspects of urban habitat. You might want to check out Wilkinson, who found a correlation of sparrow density with native shrubs in gardens, which fits in with the officially sanctioned story of urban insect decline but provides no critical evidence for it since the native shrubs could simply be providing cover.

Another paper is that of Chamberlain, which is the end product of the toil of the hapless BTO volunteers who took part in their House Sparrow survey a few years ago (and those who forked out for their House Sparrow appeal). He produces a model predicting a decline of sparrow density from around 60 per hectare where all houses have gardens to about 7 per hectare where there are no gardens, which is the basis of their well-publicised conclusion that even a small reduction in garden area will produce a catastrophic sparrow decline. Less well publicised is the solid empirical data reported in the paper, indicating a sparrow density of 2 per hectare in residential areas with gardens and slightly less in areas with no gardens whatsoever.

You could also look at the paper by Shaw, who was a BTO supervised PhD student at Exeter and produced a wonderful hand-waving exercise on the back of Chamberlain’s crazed scribblings, reading all manner of significance into the habits of the kinds of people who live in ‘back to back’ housing, though she obviously has no idea what this is. The socio-economic status angle of urban House Sparrow declines can be more easily be explained by Sparrowhawks nesting in the gardens of big posh houses.

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

Jane Turner said:

So which of the following would convince you? Merseyside, Lancashire, Derbyshire, Cheshire, Staffordshire, Clwyd, Cumbia

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Well, I really don't know. You'll have to tell me: a) What the relevant patterns are, b) What the source of the information is.

If any of the above counties showed a decrease in House Sparrow breeding numbers before and increase Sparrowhawks as part of a county avifauna breeding bird survey for example.

Jane Turner said:

If any of the above counties showed a decrease in House Sparrow breeding numbers before and increase Sparrowhawks as part of a county avifauna breeding bird survey for example.

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What a tease you are!

Like I said, I'll be very interested to take a look whenever you decide to disclose whatever it is you're on about.

Thanks Christopher, I really think there may be something in the panel fence thing, posibly not for house sparrow in particular but for garden birds in general. Rather than dive into a hedge to avoid predators, birds have to take an 'up and over' route which would certainly play into the hands (or talons) of a sparrowhawk. I suspect birds are less likely to feed in gardens (even if food is in abundance) when there is liitle cover to escape to. This is only from personal observation.

My days of T-tests and ANOVAs are thankfully over, I may try to suggest it to those I know who are still in academia.

peterbrash said:

My days of T-tests and ANOVAs are thankfully over, I may try to suggest it to those I know who are still in academia.

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I agree with you up to a point. I think the urban House Sparrow colonies that survive inside Sparrowhawk breeding territories are in places where successful hunting sorties are difficult, so it’s more than likely that there are some places that would have retained sparrows if hedges had not been removed. However I’m sceptical towards the idea that hedge removal has exacerbated the predation-related decline, since urban areas seem to be getting greener on the whole.

Nevertheless, as you say, it would be beneficial to investigate the issue, though I doubt you will find any academics with the cojones to risk the displeasure of the RSPB. I’ve searched high and low for such a creature without any success, but if you find one do put him in touch with me. (Tips on how to get articles in the Guardian would also be welcome ;-)

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

CPBell said:

However I’m sceptical towards the idea that hedge removal has exacerbated the predation-related decline, since urban areas seem to be getting greener on the whole.

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

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I realy don't understand where you get this from. There may be the odd park tree planting, or a few hanging baskets, but this would have little bearing on sparrows when thousands of miles of hedge is destroyed for parking.

CPBell said:

However I’m sceptical towards the idea that hedge removal has exacerbated the predation-related decline, since urban areas seem to be getting greener on the whole.

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As a Building Surveyor of Social Housing and LA Schools I traveled widely in the South West across Wilts, Dorset, Devon, and Somerest often traveling 200+ miles a day!
My over-riding impression over the past 7x years doesn't agree with your assertion about urban areas getting greener ? quite the reverse in my experience. I would be interested in hearing why you believe this

I just cannot see how this factor cannot have at least some significance in sparrow populations . I am surprised at how dismissive you are of any other factors that don't fit into your research on predation?

CPBell said:

I suspect there is a scientifically rigorous way of investigating the effect of hedge replacement, but if so it hasn’t yet been followed. One possibility would be to send out questionnaires to all participants in the Garden Bird Feeding Survey to ask if and when they’ve had hedges replaced by walling or fencing some time since 1970, since the theory would predict a temporal correlation with Sparrow decline across sites. I’ve no doubt that if a pattern similar to that in figure 3 of our paper emerged from such an analysis, nobody would be tying themselves in knots trying to explain it away.

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That will be because loss of habitat is generally an accepted explanation for species decline, whereas predation by a native species isn't.

If you come up with results that go against basic ecological principles, it is inevitable that you will be subject to far more scepticism, especially when the findings of your study give ammunition to anti-conservation groups.

Its interesting to see how Goldfinches are doing in comparison to House Sparrows as well as how they are doing in urban compared to rural gardens. Greenfinches were matching (though at a higher population level) them till a trichomonis outbreak interrupted their similarly meteoric rise in 2000.

Starlings on the other hand have taken a House Sparrow-like dive. Another hole nester. Perhaps just a coincidence.

(David Glue and Tim Harrison BB 103 718

spencer f said:

I realy don't understand where you get this from. There may be the odd park tree planting, or a few hanging baskets, but this would have little bearing on sparrows when thousands of miles of hedge is destroyed for parking.

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earleybird said:

I just cannot see how this factor cannot have at least some significance in sparrow populations . I am surprised at how dismissive you are of any other factors that don't fit into your research on predation?

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I’ve discussed this with Spencer previously, and as I said then, it’s nothing more than my ‘over-riding impression’. My instincts as a naturalist are no more or less valid than his. It may well be that loss of garden hedges has exacerbated predation-related sparrow decline, but the point is that there’s no scientific evidence to this effect. This is why I’m sceptical (not dismissive)! It’s my job to be sceptical about anything that doesn’t have any objective evidence to back it up.

Amarillo said:

That will be because loss of habitat is generally an accepted explanation for species decline, whereas predation by a native species isn't.

If you come up with results that go against basic ecological principles, it is inevitable that you will be subject to far more scepticism, especially when the findings of your study give ammunition to anti-conservation groups.

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It really depends on what you mean by ‘basic ecological principles’. There’s nothing in modern scientific ecology to support your assertion, but it does fit in with long-discarded notions of the ‘balance of nature’, which is a quasi-religious idea rather than a scientific principle. Part of the problem facing conservation organisations like the RSPB is that their ethos developed at a time when this was still taken seriously, and it’s therefore difficult to change their culture, particularly since religious-style myths are good for winning hearts and minds.

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

CPBell said:

It really depends on what you mean by ‘basic ecological principles’. There’s nothing in modern scientific ecology to support your assertion, but it does fit in with long-discarded notions of the ‘balance of nature’, which is a quasi-religious idea rather than a scientific principle. Part of the problem facing conservation organisations like the RSPB is that their ethos developed at a time when this was still taken seriously, and it’s therefore difficult to change their culture, particularly since religious-style myths are good for winning hearts and minds.

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This links in somewhat with where I think you're coming from, if you'll pardon my vague analysis.

One Swallow doesn't make a Summer. One Scientific study doesn't prove anything.

Science (evolutionary, geographically, medicinally etc) has always been about theories about which have been proposed which are controversial and unpopular. A status quo exists. Someone comes up with an idea which goes against the norm. They fight, get ostracised, ideas publicly debunked, then twenty years later (often after their death), suddenly new material comes to light/obfuscation declines and the idea suddenly becomes accepted.

Historically there has been a lot more personality/entrenchment/ignorance than there would be in an ideal scientifically honourable world.

Science is still akin to religion in many ways, although I think people would find it hard to accept this. Research grants are often flawed, eg bias in the way projects are decided upon in the cases of eg large multinationals (randomly, eg Glaxo Smithkline), and in the presupposition of conclusions.


One study indicating House Sparrow numbers are controlled by their predator is not indicative that it is actually the case. Only after rigorous testing of the idea and multiple studies down the line later, and maybe we could see that we have all been wrong and myth debunked ...

In ten years time, maybe we'll all be eating humble pie and admitting that we were wrong and ten years after that you will eventually be hailed the hero and be awarded the prize ...

dantheman said:

In ten years time, maybe we'll all be eating humble pie and admitting that we were wrong and ten years after that you will eventually be hailed the hero and be awarded the prize ...

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Although I don't actually believe that will be the case, sorry ...



Incidentally, your link didn't work, presumably you meant this one; http://en.wikipedia.org/wiki/Balance_of_nature ?

Quote from article;

An example of this was shown in an eight year study on small Baltic Sea creatures such as plankton, which were isolated from the rest of the ocean. Each member of the food web was shown to take turns multiplying and declining, even though the scientists kept the outside conditions constant. An article in Journal Nature stated; "Advanced mathematical techniques proved the indisputable presence of chaos in this food web ... short-term prediction is possible, but long-term prediction is not."[3]

But surely this is nothing new? The cyclical nature of predator/prey relationships such as I was taught at (primary?) school vis Lynx and Snowshoe Hare populations indicates this??

The one factor which you seem to not be taking account of in the possible interactions between the prey and predator (Hosp and Hawk) is man and his influence (ok, so that widens out into a spectrum of factors relating to nesting site, roost site (hedges), prey, agricultural changes etc etc ...).

Because they do all interact, it probably does mean that it is very difficult to unravel ONE factor as being causal. And hence to say that eg Sparrowhawk predation is THE cause of House Sparrow decline is being disingenuous to say the least ...