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

[simple]

Seems to be going around in circles here - I suggest more reading is required on the subject and the wealth of peer reviewed papers demonstrating how if the right scale of options are selected and put in the right places then farmland bird declines do reverse. Hope farm is one of a number of examples that demonstrate this in practice. (i.e. SAFFIE research amongst a wealth of others).

I would suggest you visit the farm or speak to the farm manager directly. The facts and figures speak for themselves, as do the research findings for projects such as the SAFFIE project.

After all, that is how farmers increased the population of Cirl Buntings.

From a basic understanding of ELS you can demonstrate just how easy it is for farmers to select options that they already conduct as part of good farm practice to achieve the 30 points per ha for £30 per ha. Selecting options such as skylark plots, wild bird mixes and nectar flower mixtures aren't attractive at sufficent quantities at farmscale to deliver the needed reversal in fortunes (as seen at Hope Farm).

I know the RSPB can also locally demonstrate that this can be delivered on farms in Eastern England (contact their adviser for more info). The RSPB/BTO/GWCT/NE have put together a farmland bird package (based on findings from farms such as Hope Farm) this can be found on their farm pages of the RSPB website - its trying to influence farmers to tell them exactly which options and how much they should be selecting, to make a real difference for farmland birds. The research proves that this would make the difference if a sufficent number of ELS agreements include these measures - which equates to between 3.03% - 4% of the arable area on a given farm (less than the 8% for production led set-aside).

Interestingly not to much mention of the BTO research looking at associations between predators and prey over the last 40 years from analysis of CBC and BBS data. Which as many of us are aware show actually positive correlations between prey and predator species, particularly sparrowhawks.

We now know what needs to be done all conservation organisations and government agree.....now its time to get it done...who's with us?

 

[simple]

a slight addition on set-aside, production led set-aside never halted the decline in farmland birds (like skylark). However, you can see positive responses in the Farmland Bird Indicator and this increases as the rate of set-aside increases.

Also there are 30+ peer reviewed papers on the value of set-aside for farmland birds and other wildlife. This is why the industry developed the Campaign for the Farmed Environment (which also bases its targets on the farmland bird package through ELS).

 

[mjh73]

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.

What a strange post.
C P Bells research is based on analysis of data gathered by hundreds if not thousands of Joe Public observers submitting their sightings to national survey programs.

As a member of the aforementioned Joe Public I have got involved in WeBS, black grouse surveys, Osprey monitoring, Farmyard Bunting census, Rookery census, Painted Snipe survey, shorebird surveys and Orange Bellied Parrot surveys. Every single one of these has involved me, as an unqualified volunteer, contributing my sightings to help scientists determine answers about the abundance or occurrence of birds etc.

A large part of science is about seeing stuff - of course usually in a structured way, so as to make the drawing out of answers easier or more reliable. But seeing stuff all the same. Even the guys that faff about with computer models need 'real' data from the field to build and validate the models.

At the end of the day, if there is going to be anything left to see in years to come we need to convince politicians, policy makers, developers etc that there is a need to protect and conserve. We can try and convince them using formal, structured, testable data sets and conclusions drawn from them. Or we can use informal, anecdotal here-say. They might both say the same thing, but only one has some chance of getting a hearing. The other, if anyone even knows it exists, or thinks to offer it up, is highly unlikely to be given any notice IMHO.

I am currently studying for a formal qualification in ornithology. The very first assignment we were given was..... to go out and see stuff, and try and draw some valid conclusions from what we saw.

 

[CPBell]

Deboo/Andrew Rowlands

The plastic fascia/soffit board cum cavity wall insulation caused nest site shortage theory crumbles fairly quickly in the face of what we know about sparrow decline. The demographic mechanism for decline is declining adult/1st year survival, rather than anything to do with breeding. Sparrows are often slow to adopt nest boxes when provided, which wouldn’t be expected if there were a chronic shortage of nesting opportunities. This was one of the major problems faced in the Leicester sparrow study. I also found a fairly meagre take up of nest boxes when I organised a scheme for the sparrows at London Zoo, based on the observation that they had disappeared from parts of the zoo where new buildings had replaced old. The lack of nest-box take up was one of the things that got me interested in Sparrowhawks.

King Edward

The reason that sparrows carry extra weight in winter is because it’s winter and food isn’t regular and sufficient. The carrying of extra weight is a survival mechanism to help them overcome this. However, when Sparrowhawks appear it makes them easy to pick off, so their choice is either starve or get eaten. In either case the appearance of Sparrowhawks is the change that causes increased mortality and population decline.

Simple

I don’t know what your background is, but I assume you are a sincere conservationist and an enthusiastic RSPB member – your posts are a faithful rendering of the RSPB line on these matters. All I would say to you is – don’t follow blindly. The RSPB is not infallible, and it is not a disinterested party. Where there is a divergence between the interests of the public/wildlife and the corporate interest of the RSPB or any big-business conservation body, and inevitably there will be, you can be sure which path that particular organisation will take. The members of these organisations are one of the few checks and balances available to counteract this tendency, so it’s critical that they are prepared to question the line taken. This is especially so with something like agri-environment, where the RSPB et al. have leveraged bird declines in the interest of a large-scale power grab, then gone looking for scapegoats when the promised utopia fails to emerge.

I’m more than happy to discuss any of the BTO research on predator-prey associations. Where would you like to begin?

mjh73

Good points – I would also add that although it’s perfectly valid to be sceptical of scientific findings, the scientific method is our most reliable tool for finding solutions. Conservation interests are the first to say that their policies are science-based, since they wouldn’t hold much credibility if they were’nt, which means they can only be effectively challenged from a scientific standpoint.

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

 

[simple]

CPBell I'm curious to why you draw the conclusion that I follow blindly - I have studied various aspects of this for the last 30 years I have questioned the science as the statoury bodies have, the same conclusions have been reached.

My posts are not faithful, they are fact, the issue is european wde and the solutions are tried and tested.

 

[deboo]

CP Bell,

When the BOU and RSPB et al accept your theory and the Independent posts you the 5 grand, I will be the first person on BF to congratulate you. You stick to your guns very well and I admire that. Not that I think you're right

Ludd Gang dave...

 

[King Edward]

King Edward

The reason that sparrows carry extra weight in winter is because it’s winter and food isn’t regular and sufficient. The carrying of extra weight is a survival mechanism to help them overcome this. However, when Sparrowhawks appear it makes them easy to pick off, so their choice is either starve or get eaten. In either case the appearance of Sparrowhawks is the change that causes increased mortality and population decline.

I am perfectly aware of all this, but you don't seem to have understood the point I have been making (perhaps I have been unclear). Your research has focused on the temporal connection between Sparrowhawk appearance and Sparrow decline, which I am not disputing. My point is that changes in the rural landscape (essentially, habitat simplification and loss of diversity) are likely to have increased the impact of predation on the populations of sparrows and perhaps other small bird species.

Put simply, I am suggesting that Sparrowhawk predation in a modern, agriculturally intensive landscape has more of an impact than it would in a less intensive one.

Back to the weight question, of course food is harder to come by in winter and starvation is more likely, especially for birds with lower fat reserves. But surely starvation and death are going to be even more likely in a landscape where food and cover are scarce (e.g. because seed-rich autumn stubble has been ploughed under, because seed-poor silage fields have replaced seed-rich hay meadows, because barley-eating horses have been replaced by tractors, because hedges have been flailed into see-through skeletons etc. etc.).

 

[CPBell]

Simple

I take you at your word, but I would feel more confident about doing so if I could put a cigarette paper between yourself and the RSPB PR machine. In a field like this it’s always a surprise if two independent actors ‘reach the same conclusions’, and you don’t have to march neatly in step with the RSPB to be in favour of stewardship schemes. See for instance the posts by Citrinella on pages 7 and 8 of the thread.

King Edward

No, I follow what you’re saying. As I mentioned @ #235, sparrow decline could be caused by a combination of increased predation and declining food availability. However, while we know that predation has increased, we don’t know that food has declined. We can’t measure food availability for wild animals, so we are forced to draw inferences (at the risk of incurring general wrath, this argument is set out in detail in the first part of the powerpoint here). The main piece of evidence from which food decline is inferred is sparrow decline itself, which is circular reasoning. I could equally claim intensification increases food availability because sparrows were increasing during ‘intensification’ in E. England.

Invoking Occam’s razor, therefore, the conclusion is ‘Sparrowhawks ma’am’. Anything else is just trying to patch up a crumbling hypothesis, much like the stories being told about yuppie lifestyles stealing food from the hungry beaks of urban sparrows.

 

[spencer f]

I disagree

,the leicster study proved that invertibrate food supplies can be measured.

In a measured area around the nest site, the density of native and non native shrubs, aswell as concrete and bare soil were monitored. This data correlated well with the level of invertibrates found in chick diet. It is well known that invertibrates occur in much higher densities on native perennials and shrubs. The available level of invertibrates had a MEASURED impact on chick starvation.

Privet (ligustrum Ovalifolium) is technicaly a none native, however it has grown in brittish gardens for centuries and is home to a good number of invertibrates, Privet Hawk Moth is an obvious candidate, also have you ever noticed the amount of spiders webs in privet on a dewy late summers morning.

The loss of garden habbitat over the last 30 years has been catastrophic, its impact as with that of Sparrowhawks deserves alot more study. I do not accept your dismisal of its relevance.

 

[King Edward]

I agree with spencer that food availability can be measured at least to a certain extent, although obviously on a landscape scale it could be difficult. For instance, this BTO study: The Effects of Different Crop Stubbles and Straw Disposal Methods on Wintering Birds and Arable Plants. It is perfectly reasonable to assume that an area of unploughed stubble provides more overwinter food for seed-eating birds than the same area that has been autumn-ploughed and resown. There's obviously going to be a lot of variation between the seeds available in the stubbles of different crops and depending on the number of weeds, but these things can be measured.

So, I completely reject your assertion that diminished food supply can only be assumed by way of a circular agrument on the basis that bird numbers have declined - there are good independent reasons for thinking that fewer seeds are available in a typical area of intensive arable agriculture than there would be under a less-intensive farming system.

Likewise when it comes to hedges. I don't have any figures but many, many hedges in the arable parts of Herefordshire are flailed frequently and heavily (at least once a year, perhaps more), with the result that their value to wildlife must be much diminished. Walking past tall, bushy hedges one frequently disturbs birds of several different species, but walking past the short, flailed ones it is clear that these support nothing like the same numbers or variety of species.

 

[spencer f]

Almost anything can be measured, it just requires time and effort. Quadrat surveys can be carried out on fields to determine densities of weed seeds and vegetable matter, comparisons can then be drawn with other crop types. Fields can be monitored to see which birds are using them at which times. Sparrows are easier to monitor because they are short ranging. Berry, seed and invertibrate crop comparisons can be drawn from hedges under different cutting regimes, flailed and a layed hedge for example. And of coarse chick fecal samples to establish what is being eaten and when.

 

[earleybird]

I totaly agree with KE and Spencer . We cannot simply dismiss the impact on sparrow numbers by the changes in food availability in our gardens or countryside or any other area for that matter.

I remember on my last visit to the City of london 15 years ago that sparrows were at absolute plague proportions , worse than pigeons! and an absolute menace. What has changed in that envionment that has effected their numbers so much ?

Theories are all well and good but what we desperately need is more information from comprehensive short and long term studies over the whole gamut of environments throughout the British Isles which regretably we do not, and will never have.

I'm sure that the rise in BOP must have had a devastating effect on sparrow and other small bird numbers over the last 15-20 years or so but there must be much more to it than that surely.

In the past week or so I have watched a number of programs on on TV about our studies into the decline of many British species including the eel .

How is it that one of the toughest & hardiest survivors we have is in such catastrophic decline ? Eels can climb into a lump of moist mud and survive a drought for crissakes. They swim all the way to the Sargasso sea and back and yet according to a 10 year study their numbers have declined by apparently 98% in recent years??:eek!: What on earth could be effecting such a hardy animal when our rivers are cleaner richer envionments than they have been for decades

There is some very strange things going on in the world which we are clearly at a loss to explain.

 

[CPBell]

Spencer

The Leicester study did show a correlation between aphid density and nestling survival, but you can’t infer from this that food shortage is a cause of population decline. Let me illustrate.

Imagine a sparrow nest with a conveyor belt running past it on which there are mealworms. The only thing constraining the number of nestlings that can be raised is the rate at which the adults can pick up mealworms and stuff them into their mouths. A pair might be able to raise 100 nestlings at once. Imagine another nest with a much slower conveyor belt. Here the pair can only raise 50 nestlings because they have to wait longer for mealworms. There is also a still slower conveyor belt where a pair can only raise 25 nestlings. There is a perfect correlation between food availability and nestling survival, so the population must be declining because of food shortage, right? Not very likely if a pair can raise a minimum of 25 offspring at a time.

King Edward

You need to be a little careful when relying on ‘grey literature’ such as the report you cited, especially when it’s from the BTO. Very little of their fat, taxpayer-funded report on sparrow decline made it through to the peer-reviewed literature, and given the weasel words that pepper the abstract of this one I wouldn’t be surprised if the same applies here.

I seems to say (I won’t be rushing to fork out the £10 it costs) that there are more weeds in fields where less weed-killer is used, so there are more seeds in those fields, and sometimes there are more birds in fields with more seeds, therefore birds must have declined because of increased use of weedkiller, and would increase if it were used less. However this is only true if weed seeds in arable fields are a limiting resource, which can’t be deduced from the fact that birds are attracted to fields with lots of seeds. It may be that without such fields they would feed somewhere else and survive equally well.

Earleybird

The thing that’s changed in the last 15 years is that Sparrowhawks have started nesting in all the central London parks, as well as in large gardens and private grounds throughout the city centre.

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

 

[Brian Stone]

I suspect eel declines correlate with the increase in Sparrowhawks. You have your culprit!

I'm also struggling to remember ever seeing a Sparrowhawk take a House Sparrow, plenty of thrushes, columbidae, etc. though. We also have a fairly healthy House Sparrow population where I live and a lot of Sparrowhawk activity but then we also have a lot of ivy-clad walls and 'wild' gardens. Only another anecdotal report of course.

 

[earleybird]

I suspect eel declines correlate with the increase in Sparrowhawks. You have your culprit!

:-O:-O:-O

you seem to have pretty similar enviornment to me . I'd be curious to know what recorded field data the Sprawk hypothesis is actually based on because we have Sprawks nesting next door for 5 years now and our sparrow population is very healthy and shown no significant decline over the past 12 years that I have noted. On the three occasions I have seen a Sprawk kill in my garden the birds taken were thrush blackbird and starling ...My wife did witness a Peregrine kill in front of her horse when she was out hacking once but that is another story !

 

[James_Owen]

You need to be a little careful when relying on ‘grey literature’ such as the report you cited, especially when it’s from the BTO. Very little of their fat, taxpayer-funded report on sparrow decline made it through to the peer-reviewed literature, and given the weasel words that pepper the abstract of this one I wouldn’t be surprised if the same applies here.

You know what's well weird about this thread? It's the way CPBell seems to think using such sensational and unguarded language discredits his opponents and not him.
Even if he has a point who'd believe the guy?

BTW, it's entirely unscientific but I'll add that my garden is also full of sparrows, I see sprawk activity every week, and the street is full of gardens with all the vegetation you'd like to see.
The unweary blackbirds have had a tough time of it though.

 

[Frenchy]

I've followed this thread for a while, and what the heck is going on?

To an amateur ornithologist like me and seemingly most people on this thread, the house sparrow decline is most likely attributable to a wide variety of contributory factors, including:
* loss of urban habitat
* decrease in available invertebrate prey due to increased use of pesticides and decline in urban habitat
* loss of nest sites
* decline in rural food availability

Just because these factors are difficult to measure and quantify does not mean that you can just discount them.

Here's a thought. About 20 years ago (i think?), many people in Wolverhampton were sold a nice aerial photo of their house. Surely it would be possible to get hold of early aerial images and then measure differences in urban vegetation cover against google earth images of modern urban area. That can't be rocket science as i've just thought of it! Just involves a bit of detective work rather than looking at numbers and nothing else.

No matter how good the correlation between house sparrow decline and the revival of sparrowhawk numbers appears, it doesn't guarantee that this is the sole cause, or even a contributory factor. To take that sort of logic to its extreme, i could state that drinking milk as a child will always lead to heroin addiction. The link is clear, and i'm just conveniently ignoring the huge number of other factors which might contribute to taking up smack.

CP Bell wrote:

The Leicester study did show a correlation between aphid density and nestling survival, but you can’t infer from this that food shortage is a cause of population decline. Let me illustrate.

Imagine a sparrow nest with a conveyor belt running past it on which there are mealworms. The only thing constraining the number of nestlings that can be raised is the rate at which the adults can pick up mealworms and stuff them into their mouths. A pair might be able to raise 100 nestlings at once. Imagine another nest with a much slower conveyor belt. Here the pair can only raise 50 nestlings because they have to wait longer for mealworms. There is also a still slower conveyor belt where a pair can only raise 25 nestlings. There is a perfect correlation between food availability and nestling survival, so the population must be declining because of food shortage, right? Not very likely if a pair can raise a minimum of 25 offspring at a time.

I must be being a bit dense tonight, as i have no idea what you're trying to infer from this.

Also, if the RSPB were so frightened of upsetting their members, why did they agree to the ruddy duck cull? The answer is because they thought the science was sound.

And just to add my entirely unscientific observations to the debate, i have also never seen a sparrowhawk take a sparrow. Thrushes, blackbirds, tits yes. But never a sparrow. Perhaps that should be the next study...

Those are just my thoughts on this, but i really would like further clarification on the aphid issue.

 

[PhilW]

I've followed this thread for a while, and what the heck is going on?

To an amateur ornithologist like me and seemingly most people on this thread, the house sparrow decline is most likely attributable to a wide variety of contributory factors, including:
* loss of urban habitat
* decrease in available invertebrate prey due to increased use of pesticides and decline in urban habitat
* loss of nest sites
* decline in rural food availability

Just because these factors are difficult to measure and quantify does not mean that you can just discount them.

Here's a thought. About 20 years ago (i think?), many people in Wolverhampton were sold a nice aerial photo of their house. Surely it would be possible to get hold of early aerial images and then measure differences in urban vegetation cover against google earth images of modern urban area. That can't be rocket science as i've just thought of it! Just involves a bit of detective work rather than looking at numbers and nothing else.

No matter how good the correlation between house sparrow decline and the revival of sparrowhawk numbers appears, it doesn't guarantee that this is the sole cause, or even a contributory factor. To take that sort of logic to its extreme, i could state that drinking milk as a child will always lead to heroin addiction. The link is clear, and i'm just conveniently ignoring the huge number of other factors which might contribute to taking up smack.



I must be being a bit dense tonight, as i have no idea what you're trying to infer from this.

Also, if the RSPB were so frightened of upsetting their members, why did they agree to the ruddy duck cull? The answer is because they thought the science was sound.

And just to add my entirely unscientific observations to the debate, i have also never seen a sparrowhawk take a sparrow. Thrushes, blackbirds, tits yes. But never a sparrow. Perhaps that should be the next study...

Those are just my thoughts on this, but i really would like further clarification on the aphid issue.

Paul,

Like you I understand the various factors affecting a decline in House Sparrow numbers - including loss of nesting sites where old soffit boards are replaced with new PVC ones eliminating nesting holes. Something that wouldn't show up on aerial photographs. :t:

I was also taught about predator prey relationships. Predator populations (be it Lions, Tigers or Sparrowhawks) are limited by the number of prey individuals. A good example used by all good Zoology / Biology Undergraduates is the White-tailed Deer population in N America which exploded with the demise of Wolves but then crashed when food & habitat were in short supply - overgrazing by a burgeoning deer population meant there wasn't enough food to go around so the population fell.

Its ridculous and frankly sensationalism to blame the demise of many song bird populations on an increase in Sparrowhawk numbers. The odds are a Sparrowhawk will kill a commoner species as it comes across those more readily - in our case Collared Doves and, if its a big female Sparrowhawk, Wood Pigeon. Sparrowhawks are top of the avian food chain in most gardens and their numbers will only continue to increase as long as there is prey. If prey numbers significantly reduce the Sparrowhawk population will ultimately decline and so the circle begins again.

 

[Frenchy]

Paul,

Like you I understand the various factors affecting a decline in House Sparrow numbers - including loss of nesting sites where old soffit boards are replaced with new PVC ones eliminating nesting holes. Something that wouldn't show up on aerial photographs. :t:

No, but any loss of vegetation cover would :t:

There are several well documented predator/prey relationships, and the one i was taught was snowshoe hares and lynx. I guess these are mainly applicable where you have a dedicated predator/prey relationship, which is not the case with sparrowhawk and house sparrow. Although i admit i'm not a scientist by any stretch!

 

[CPBell]

CPBell seems to think using such sensational and unguarded language discredits his opponents and not him. Even if he has a point who'd believe the guy?

I’m sorry I gave that impression (where)? I think I try to persuade my opponents by pointing out errors of fact or logic in their arguments. Like the fallacy of pseudo-refuting descriptions, for instance.

Try this as an example: A number of contributors have doubted whether Sparrowhawks take many Sparrows, because they see them taking thrushes or pigeons much more often. However, this is because they are more likely to notice when the prey are large enough to put up a fight. I’ve seen Sparrowhawks take Sparrows a few times. They snatch them up with hardly a missed wingbeat , and then carry them off to a nice secluded plucking post. Blink and you miss it, but proper controlled studies repeatedly show that House Sparrows are by far the preferred prey of Sparrowhawks when they are available.

There is also a widespread misconception that Sparrowhawks predation hypothesis predicts that Sparrows and Sparrowhawks can never coexist under any circumstances, so is refuted by the fact that ‘my garden has Sparrows and I see Sparrowhawks every day’. There were many examples in the dataset where Sparrows did not decline with Sparrowhawks present, but where they appeared in a site after previously being absent, the average trend was an inexorable decline.

Frenchy

The conveyor belt argument was in answer to a post from Spencerf on the paper by Peach of the RSPB. To understand it you really need to read the paper, or failing that, take a look at this. The Leicester study written up in Peach et al. exemplifies what generally happens in ecological, and especially bird studies, which is that people rush out into the field and collect a load of data, and while analysing this and writing it up realise that it doesn’t actually answer the question they were asking in the first place, which they then proceed to conceal by means of fancy statistics and sophistical argumentation.

PhilW

The reality is that nature doesn’t always follow the pat formulae taught to undergraduates. The ‘predators require healthy prey populations’ is a favourite of the RSPB, but if it were true, no predator would ever be able to drive a prey species to extinction. However this has happened time and again with introduced predators all over the world. Take as an example the Socorro Dove. You can see this in the Zoo, but not on Socorro Island, where it was wiped out by cats. The fact that the cats are still there is the main thing preventing a reintroduction programme. There must still be things there that the cats can eat, so why didn’t they switch to these when Socorro Doves became rare? Maybe they haven’t read the text books?

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