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Sparrowhawks responsible for House Sparrow decline says scientist (1 Viewer)
- Thread starter John B (not the sloop)
- Start date
I have not read the original paper , but does it take into account the major decline in house sparrows in the early 20th centuary. This was driven by the change over from the horse to the car. Horses were the main method of transporting goods in cities. They were fed with nose bags during the working day and horses are wasteful feeders. This major food source was lost with the change over to the car. In more recent years sparrows have been further denied food as modern hygene demands corn is kept apart from pests , both animal and bird. Grain silos now have no access for birds and grain has become so valuable that today spillage from lorries is almost non existant. Couple that with much shorter harvest periods and the sparrow has undergon a major loss of food sources.
Of course that has be countered to some extent by the provision of bird feeders , but even here there have been changes. While corn grains are doubtless better food than bread when i was a kid most people chucked out stale bread crusts for the birds instead. Of course sparrows love bread perhaps more than wheat ( its easy to handle and digest ) , but today we see fewer people feeding " unhealthy " bread prefering
" healthy " sunflower seeds and corn.
The other major change is the change in house roofing. In the past they could nest under the pan tiles of most houses. Today they cannot get into the roofs of modern houses. Less easy to explain is the desertion of hedge nesting colonies. When i was young it was a common sight. But i have not seen one for 20 years.
Sparrowhawks may have a small impact on house sparrows , but I very much doubt if it is a major cause of their decline.
Of course that has be countered to some extent by the provision of bird feeders , but even here there have been changes. While corn grains are doubtless better food than bread when i was a kid most people chucked out stale bread crusts for the birds instead. Of course sparrows love bread perhaps more than wheat ( its easy to handle and digest ) , but today we see fewer people feeding " unhealthy " bread prefering
" healthy " sunflower seeds and corn.
The other major change is the change in house roofing. In the past they could nest under the pan tiles of most houses. Today they cannot get into the roofs of modern houses. Less easy to explain is the desertion of hedge nesting colonies. When i was young it was a common sight. But i have not seen one for 20 years.
Sparrowhawks may have a small impact on house sparrows , but I very much doubt if it is a major cause of their decline.
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It is pretty much accepted that the change from horse to engine is responsible for the sparrow decline in the first half of the twenteith century.
The change in supplementary feeding habbits is interesting, a lot of people no longer feed bread to birds and I wonder if this is significant, having said that I still see sparrows going mad for mixed seed. The argument has been which factor is most responsible for the decline over the last 30 years.
More paving in gardens = Reduced invertibrates for nestlings
Pannel fences replacing hedges = Less colonial nesting sites
Law restricting height of evergreen hedging = less protection from predators
More cats = Pressure on breeding populations
More magpies
More raptors
More modern rooves and loft insulation = Less cavity nesting
More pigeons = More competition for traditional
food supplements
The change in supplementary feeding habbits is interesting, a lot of people no longer feed bread to birds and I wonder if this is significant, having said that I still see sparrows going mad for mixed seed. The argument has been which factor is most responsible for the decline over the last 30 years.
More paving in gardens = Reduced invertibrates for nestlings
Pannel fences replacing hedges = Less colonial nesting sites
Law restricting height of evergreen hedging = less protection from predators
More cats = Pressure on breeding populations
More magpies
More raptors
More modern rooves and loft insulation = Less cavity nesting
More pigeons = More competition for traditional
food supplements
The article only addresses the post-1970 trend, and I don’t dispute the explanation for early 20th century urban sparrow decline. I wouldn’t recommend you read the article unless you have a background in ecological science, but it’s here nevertheless. You might instead be interested to take a look at a powerpoint presentation that tackles the alternative hypotheses and sets out the article’s main findings.
The BTO in particular has tried to patch together a scenario based on different aspects of agriculture as they apply in different parts of the country, including grain silos, switch to autumn sowing, more efficient harvesting methods, variation in livestock levels etc. When they go looking for evidence, however, they find it isn’t there, but they bury the findings away in voluminous reports that no-one will ever read, while continuing to push their hand-waving scenario to keep the government cash flowing. The fact that you’ve reproduced aspects of it here is testimony to their success.
http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
Having now read your paper i feel there are a number of issues that need to be addressed from it.
CP Bell quote “I disagree with the proposition that a decline in food abundance has caused House Sparrow populations to collapse.”
As I have said in a previous post the type of food we put out for birds has changed greatly in the past 30 years. Bread is eaten by a range of garden birds , but especially sparrows. Finches and tits will feed on it too , but in my experience will always go for seed food first. Bread has a quick handling time for sparrows who have to de-shuck seeds before eating them. Bread is now an uncommon garden bird food and with the increasing trend for countryside birds to move into gardens house sparrows have far more competition for other foods. I can remember as a child in London that in the parks almost all the birds coming to the bread we fed the birds were sparrows and feral pigeons with only the odd finch or robin and blackbird. Now living in a sub-urban garden in Norfolk sparrows have to compete with a wide range of competitors on my feeders.
Back in the 1960 we always used to lose most of our garden sparrows to the farmland corn fields in late summer. this practice has almost stopped in my area. The modern harvest is very short and stubbles quickly ploughed in. In the past harvest could last 2 1\2 months . Today the harvest can be as short as 4 weeks some years and a farmer aims to leave less that 1% of his harvest in the stubble. 30 years ago it was over 5%. Grain silos have to be sealed from vermin to meet hygiene standards these days. Years ago the corn was shot onto the barn floor and birds had easy access to it in most cases. That adds up to a lot less available food and I would argue will have more of an impact on sparrows which unlike most other farmland birds would be happy to enter buildings for food.
CP Bell quote “it is unarguable that there has been a vast increase in urban litter”
This might be true , but what type or use is it going to be to sparrows. I would suggest that corn derived food in urban areas in rubbish is unchanged over the past 40 years.
CP Bell quote “The numbers of Sparrowhawks in Britain has increased approximately four-fold since the early 1960s.”
This is true , but prior to this sparrowhawks had been a fairly widespread rural bird of prey present on most farms and yet sparrows were common in both rural and urban areas.
CP Bell quote “Sparrowhawks became noticeably more common in wartime when gamekeeping declined.”
In which case using your argument there should have been a initial post war boost in sparrow numbers. As far as I am aware sparrows were flat lining after the early 20th century decline until about 25 years ago.
The graph shows a interesting picture , but what it does not show is comparable numbers. If this a was included the same trend would emerge , but the sparrowhawks lines would be restricted to the bottom fraction of the graph while the sparrow graph would be pushing at the top. An interesting manner in which stats can twist values.
CP Bell quote “Sparrow populations in the south and east lived for a minimum of several decades without any experience of predation by Sparrowhawks. Under these conditions the most successful individuals would have been those that were less vigilant, and more inclined to take risks to secure resources, such as feeding out in the open away from cover. When Sparrowhawks finally returned, therefore, they found sparrow populations that had lost their predator averse behaviour, and were therefore all too easy to pick off.”
This is very true , but is their any reason why sparrows cannot adapt to increased predation risk in the same manner other birds such as tits have , by becoming more agile. One thing I quickly learnt while ringing house sparrows is they are very quick learners. A net set one week in a new spot would result in very high catches . In the second week a hand full would be caught and by the third week is was a waste of time attempting to catch any further members of the flock as they had become very wary of a mist net. This shows a high level of adaptability.
CP Bell quote “This explains why the steepest Sparrow declines have occurred in arable areas, because it is these areas in particular from which Sparrowhawks were extirpated by heavy use of pesticides as seed dressings.”
O what a sweeping statement. If all ecology was so simple. It does nothing of the sort, there are a lot of other factors involved here from changes in farming methods , new crops , pesticides , landscape changes …….. I could go on zzzzzzzz.
CP Bell quote “It has often been noted that Sparrows seem to cling on better in less affluent areas of cities. They disappear from leafy suburbs, but continue to thrive in sprawling council estates. The reason is that affluent areas provide nesting opportunities for Sparrowhawks, because they contain large gardens, private grounds, and well-managed parkland where the hawks can nest safely.”
You are correct affluent areas with large gardens\trees suit sparrowhawks better. But Less affluent areas tend to have a high percentage of old style roofs with pan tiles that are far more suitable for house sparrows to nest in. One of my ex students some years ago under took a study of the sparrow clans in his village. He found there was a very strong coloration between roof type and sparrow nesting areas. And in one case an old large warehouse was replaced by new houses with sealed roofs. The result the sparrow clan that lived in that area dispersed within a year of the new development being completed. The two other clans in his village were all centered in areas of old style pan tiles. So I would sugest its nesting habitat rather than predation that would explain your statment.
Perhaps I should make clear now I used to lecture in ecology and ornithology at the UEA and use to use house sparrows as a case study in urban ecology. As a result several students
( New fledgling ecologists with open minds ) went off to do their final research paper on house sparrows which resulted in more data for the following years students to work on. You have presented some worth wile arguments on sparrowhawk predation of house sparrows , but if a student of mine had presented such data I would have not marked him very highly as the subject has been approached in a rather blinkered manner.
You have fallen into the same trap as the BTO in taking a one dimensional look at the problem. In the BTOs case looking at a more local problem , not nation wide in your case looking only at the present day situation without a close study to important factors of the past. Long running data sets are as important to ecology as up to date research.
Yes sparrowhawks do kill house sparrows and may have some local impacts , but sparrowhawks are hardly what you would call abundant in comparison with house sparrows and any inroads they make should be within the capabilities of a healthy sparrow population to absorb. I suspect in reality the answer is a cocktail of several factors, increased competition in urban areas , reduced nesting habitats , changes in food type and supply and of course predation not just from hawks , but also from cats will have had an additive effect.
Population , predator and prey models are only as good as the data put into them and are easily open to mistaken conclusions and without good solid supporting evidence I would take a questioning view of them. History has produced some classic mistakes in such models , for example the WWTs claim that pink footed geese would never exceed 70,000 individuals. With a population more than treble that it can be seen that great caution needs to be placed in such data. Going out and collecting your own data in the field and then seeing if that fits into your model might produce more reliable results.
One piece of anecdotal evidence. I used to have a clan of 50-80 house sparrows in my garden. They disappeared when a old nesting building close by was pulled down 20 years ago. After a 9 year absence small numbers have returned using boxes on a shed nearby. During this time sparrowhawks have been a unchanged but regular and uncommon visitor to my bird table , maybe a dozen sightings a year. There is no suggestion that their presence has any impact on house sparrow numbers in my garden.
PS, none of the links you provide on your site can be located on my browser. All say NOT FOUND.
CP Bell quote “I disagree with the proposition that a decline in food abundance has caused House Sparrow populations to collapse.”
As I have said in a previous post the type of food we put out for birds has changed greatly in the past 30 years. Bread is eaten by a range of garden birds , but especially sparrows. Finches and tits will feed on it too , but in my experience will always go for seed food first. Bread has a quick handling time for sparrows who have to de-shuck seeds before eating them. Bread is now an uncommon garden bird food and with the increasing trend for countryside birds to move into gardens house sparrows have far more competition for other foods. I can remember as a child in London that in the parks almost all the birds coming to the bread we fed the birds were sparrows and feral pigeons with only the odd finch or robin and blackbird. Now living in a sub-urban garden in Norfolk sparrows have to compete with a wide range of competitors on my feeders.
Back in the 1960 we always used to lose most of our garden sparrows to the farmland corn fields in late summer. this practice has almost stopped in my area. The modern harvest is very short and stubbles quickly ploughed in. In the past harvest could last 2 1\2 months . Today the harvest can be as short as 4 weeks some years and a farmer aims to leave less that 1% of his harvest in the stubble. 30 years ago it was over 5%. Grain silos have to be sealed from vermin to meet hygiene standards these days. Years ago the corn was shot onto the barn floor and birds had easy access to it in most cases. That adds up to a lot less available food and I would argue will have more of an impact on sparrows which unlike most other farmland birds would be happy to enter buildings for food.
CP Bell quote “it is unarguable that there has been a vast increase in urban litter”
This might be true , but what type or use is it going to be to sparrows. I would suggest that corn derived food in urban areas in rubbish is unchanged over the past 40 years.
CP Bell quote “The numbers of Sparrowhawks in Britain has increased approximately four-fold since the early 1960s.”
This is true , but prior to this sparrowhawks had been a fairly widespread rural bird of prey present on most farms and yet sparrows were common in both rural and urban areas.
CP Bell quote “Sparrowhawks became noticeably more common in wartime when gamekeeping declined.”
In which case using your argument there should have been a initial post war boost in sparrow numbers. As far as I am aware sparrows were flat lining after the early 20th century decline until about 25 years ago.
The graph shows a interesting picture , but what it does not show is comparable numbers. If this a was included the same trend would emerge , but the sparrowhawks lines would be restricted to the bottom fraction of the graph while the sparrow graph would be pushing at the top. An interesting manner in which stats can twist values.
CP Bell quote “Sparrow populations in the south and east lived for a minimum of several decades without any experience of predation by Sparrowhawks. Under these conditions the most successful individuals would have been those that were less vigilant, and more inclined to take risks to secure resources, such as feeding out in the open away from cover. When Sparrowhawks finally returned, therefore, they found sparrow populations that had lost their predator averse behaviour, and were therefore all too easy to pick off.”
This is very true , but is their any reason why sparrows cannot adapt to increased predation risk in the same manner other birds such as tits have , by becoming more agile. One thing I quickly learnt while ringing house sparrows is they are very quick learners. A net set one week in a new spot would result in very high catches . In the second week a hand full would be caught and by the third week is was a waste of time attempting to catch any further members of the flock as they had become very wary of a mist net. This shows a high level of adaptability.
CP Bell quote “This explains why the steepest Sparrow declines have occurred in arable areas, because it is these areas in particular from which Sparrowhawks were extirpated by heavy use of pesticides as seed dressings.”
O what a sweeping statement. If all ecology was so simple. It does nothing of the sort, there are a lot of other factors involved here from changes in farming methods , new crops , pesticides , landscape changes …….. I could go on zzzzzzzz.
CP Bell quote “It has often been noted that Sparrows seem to cling on better in less affluent areas of cities. They disappear from leafy suburbs, but continue to thrive in sprawling council estates. The reason is that affluent areas provide nesting opportunities for Sparrowhawks, because they contain large gardens, private grounds, and well-managed parkland where the hawks can nest safely.”
You are correct affluent areas with large gardens\trees suit sparrowhawks better. But Less affluent areas tend to have a high percentage of old style roofs with pan tiles that are far more suitable for house sparrows to nest in. One of my ex students some years ago under took a study of the sparrow clans in his village. He found there was a very strong coloration between roof type and sparrow nesting areas. And in one case an old large warehouse was replaced by new houses with sealed roofs. The result the sparrow clan that lived in that area dispersed within a year of the new development being completed. The two other clans in his village were all centered in areas of old style pan tiles. So I would sugest its nesting habitat rather than predation that would explain your statment.
Perhaps I should make clear now I used to lecture in ecology and ornithology at the UEA and use to use house sparrows as a case study in urban ecology. As a result several students
( New fledgling ecologists with open minds ) went off to do their final research paper on house sparrows which resulted in more data for the following years students to work on. You have presented some worth wile arguments on sparrowhawk predation of house sparrows , but if a student of mine had presented such data I would have not marked him very highly as the subject has been approached in a rather blinkered manner.
You have fallen into the same trap as the BTO in taking a one dimensional look at the problem. In the BTOs case looking at a more local problem , not nation wide in your case looking only at the present day situation without a close study to important factors of the past. Long running data sets are as important to ecology as up to date research.
Yes sparrowhawks do kill house sparrows and may have some local impacts , but sparrowhawks are hardly what you would call abundant in comparison with house sparrows and any inroads they make should be within the capabilities of a healthy sparrow population to absorb. I suspect in reality the answer is a cocktail of several factors, increased competition in urban areas , reduced nesting habitats , changes in food type and supply and of course predation not just from hawks , but also from cats will have had an additive effect.
Population , predator and prey models are only as good as the data put into them and are easily open to mistaken conclusions and without good solid supporting evidence I would take a questioning view of them. History has produced some classic mistakes in such models , for example the WWTs claim that pink footed geese would never exceed 70,000 individuals. With a population more than treble that it can be seen that great caution needs to be placed in such data. Going out and collecting your own data in the field and then seeing if that fits into your model might produce more reliable results.
One piece of anecdotal evidence. I used to have a clan of 50-80 house sparrows in my garden. They disappeared when a old nesting building close by was pulled down 20 years ago. After a 9 year absence small numbers have returned using boxes on a shed nearby. During this time sparrowhawks have been a unchanged but regular and uncommon visitor to my bird table , maybe a dozen sightings a year. There is no suggestion that their presence has any impact on house sparrow numbers in my garden.
PS, none of the links you provide on your site can be located on my browser. All say NOT FOUND.
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It would appear that you've read the sparrow pages on my website rather than the paper itself. The website is certainly the source of all the quotes you've cited. Nevertheless, I'll see if I can address your points. The links in my earlier post are working fine for me both in Explorer and Chrome.
Here are the first two passages you quoted in their original context, with the most important point in bold:
Food availability for wild animals is notoriously difficult to measure, and few of the studies citing food abundance as a cause make any attempt to measure it directly. Instead, evidence is presented in the form of proxy variables that are thought to provide an index of food abundance. For rural sparrow populations, in common with those of a variety of declining farmland birds, changes in agricultural practices are cited, including increased use of herbicide and insecticide, and changes in sowing and harvesting regimes. For urban sparrow populations, the main factors are said to be conversion of front gardens for off-road parking, development of brownfield sites, and planting of ornamental shrubs, all leading to a lack of insects to feed nestlings.
I disagree with the proposition that a decline in food abundance has caused House Sparrow populations to collapse. There is little or no critical evidence to suggest that this is the case, and arguably such evidence is impossible to obtain, since there are so many potential covariates of any of the proxy indices that have been used for food abundance. For urban areas in particular, it could be argued that the environment has become greener, with better air quality over the period of sparrow decline, and it is unarguable that there has been a vast increase in urban litter, with commensurate feeding opportunities for Sparrows.
Your list of anecdotes could be construed as a reason for entertaining the proposition that food has declined, just as the litter anecdote could be a reason for thinking it has increased, but my point is that there is no objective evidence (i) that food has become a more limiting factor (ii) that this has contributed to their decline. As a former UEA lecturer, I'm sure you understand the difference.
The next two quotes are taken from the following passage:
The numbers of Sparrowhawks in Britain has increased approximately four-fold since the early 1960s. Prior to this the species had undergone its own catastrophic decline, caused by the residues of pesticides introduced just after the Second World War.
No census data are available earlier than this, so we have no idea how many Sparrowhawks there were in Britain, but we do know that they were heavily persecuted, partly because they became noticeably more common in wartime when gamekeeping declined.
It's also relevant that we don't have census data for sparrows, so we cannot say whether the short-term wartime recovery of sparrowhawks had any effect. The point is that sparrowhawks were heavily persecuted prior to 1960, and rural sparrows had not had time to lose predator averse behaviour.
I've attached the plot for convenience, but I think you're trying a little too hard here. Even the current ratio is 500:1. Are you seriously suggesting the species should be graphed on the same scale, or that a predator can't affect prey unless it occurs at a similar density?
Your quibbles over regional and urban variation are missing the point. The distinctive patterns in house sparrow decline on a variety of scales can be explained by a rococo patchwork of divergent variables on the one hand, or on the other hand by sparrowhawks, so the latter is preferable on grounds of parsimony.
Just so we're all clear that's the UNIVERSITY OF EAST ANGLIA folks, tuition fees £3,750 p.a.
Attachments
I followed the link you yourself provided and based my comments on the site it brought up. I think it is reasonable to assume that your website and paper come with the same arguments and the same conclusions . If this is not the case then the your work must be discounted.
CJ BELL Quote “I disagree with the proposition that a decline in food abundance has caused House Sparrow populations to collapse. There is little or no critical evidence to suggest that this is the case”
On the contrary there is plenty of evidence if you care to look for it ( try looking at DEFRA data ) the amount of grain left after the harvest has declined by 80% in the past 25 years . Indeed one possible reason why corn buntings seem to be doing best in intensive arable areas compared to less productive farmland is the difference in yields between these two farm types. In intensive West Norfolk or Fenland farmland yields of 10 tones per ha are not unusual. In West Wales 2.25-3 tons per Ha is the average yield. When modern harvesting leaves about only 1% of the crop on the field its clear that 1% of 10 tones per ha is a lot more that 1% of 2.25-3 tons. And despite on average smaller fields and plenty of “ wild “ hedges\field boundary corn bunting are doing better in the more intensive areas despite large fields and close cut hedges with little natural food.
I helped a PhD student looking into the decline of buntings back in the 1990s and We did a lot of work on seed availibity for finches and buntings by sampling seed density and depletion across a selection of arable fields. We found a depletion of over 80% during the course of the year and much less that other studies had found a decade beforehand. Of course to provide a reliable bench mark the same fields and crop types need to be sampled over 20 years or more , but there was good evidence to suggest a sharp drop in the amount of available food compared with past years. This might have a more profitable course of action for your study rather than relying on pure stats. When you do the work yourself you get a far more clear picture of your results and maintain a more balanced view on the subject you are studying.
I would suggest that your statement “There is little or no critical evidence to suggest that this is the case” is because you have not looked for it in the right place. Or better still go out and look for it yourself before condemning such evidence.
Litter
I would suggest you have a look at the type of litter you can find in urban areas. I have never quantified its type , but from what I have seen its mainly potato \ fish\ chicken based rather than corn based , so it would produce very little in the way suitable of sparrow food. If the work has not been done then you need to do it before making claims that sparrowhawks are to blame for the decline in house sparrows as your actions could if certain groups use your work to push for culling of sparowhawks.
CJ Bell Quote "I've attached the plot for convenience, but I think you're trying a little too hard here. Even the current ratio is 500:1. Are you seriously suggesting the species should be graphed on the same scale, or that a predator can't affect prey unless it occurs at a similar density? "
To the layman that graph is very convincing , but with no quantifying legend ( apart from time ) how do you expect it to be understood correctly. Its basic stats a graph has to have a X and Y legend or it is open to different interpretations .
CJ Bell quote “Just so we're all clear that's the UNIVERSITY OF EAST ANGLIA folks, tuition fees £3,750 p.a.” Just what has that to do with the subject in hand.
While I was there the UEA was nationally recognised as one of the top universities to study ecology in the country bettered only by Oxford and Cambridge. That did not stop those universities offering lecturing jobs to several of the UEAs lecturers. It’s a very juvenile statement you have made not worthy of a schoolboy let alone someone who is supposed to be mature.
One of the major objectives I always imparted into my students was to question everything you read or I taught and form a balanced opinion of their own , not to go blindly on with a closed mind. It’s a lesson some others would do well to follow.
You have some good points , but not enough to prove your case. These are to many other variables in play that could be affecting house sparrows decline and you seem to claim that if the evidence is not available other causes cannot counted. If the evidence is not available , then before making such possibly damaging claims that could result in sparrowhawk control go and do the work yourself. Come back with a balanced paper with all the other variables explored , then make your claims. Exploration of stats and population models is only half the job and needs to be supported with hard field work. And you wondered why the paper rejected your work !
In short Job only half done. Well I have to get on with my own data inputs now from a day in the field with wild geese!
CJ BELL Quote “I disagree with the proposition that a decline in food abundance has caused House Sparrow populations to collapse. There is little or no critical evidence to suggest that this is the case”
On the contrary there is plenty of evidence if you care to look for it ( try looking at DEFRA data ) the amount of grain left after the harvest has declined by 80% in the past 25 years . Indeed one possible reason why corn buntings seem to be doing best in intensive arable areas compared to less productive farmland is the difference in yields between these two farm types. In intensive West Norfolk or Fenland farmland yields of 10 tones per ha are not unusual. In West Wales 2.25-3 tons per Ha is the average yield. When modern harvesting leaves about only 1% of the crop on the field its clear that 1% of 10 tones per ha is a lot more that 1% of 2.25-3 tons. And despite on average smaller fields and plenty of “ wild “ hedges\field boundary corn bunting are doing better in the more intensive areas despite large fields and close cut hedges with little natural food.
I helped a PhD student looking into the decline of buntings back in the 1990s and We did a lot of work on seed availibity for finches and buntings by sampling seed density and depletion across a selection of arable fields. We found a depletion of over 80% during the course of the year and much less that other studies had found a decade beforehand. Of course to provide a reliable bench mark the same fields and crop types need to be sampled over 20 years or more , but there was good evidence to suggest a sharp drop in the amount of available food compared with past years. This might have a more profitable course of action for your study rather than relying on pure stats. When you do the work yourself you get a far more clear picture of your results and maintain a more balanced view on the subject you are studying.
I would suggest that your statement “There is little or no critical evidence to suggest that this is the case” is because you have not looked for it in the right place. Or better still go out and look for it yourself before condemning such evidence.
Litter
I would suggest you have a look at the type of litter you can find in urban areas. I have never quantified its type , but from what I have seen its mainly potato \ fish\ chicken based rather than corn based , so it would produce very little in the way suitable of sparrow food. If the work has not been done then you need to do it before making claims that sparrowhawks are to blame for the decline in house sparrows as your actions could if certain groups use your work to push for culling of sparowhawks.
CJ Bell Quote "I've attached the plot for convenience, but I think you're trying a little too hard here. Even the current ratio is 500:1. Are you seriously suggesting the species should be graphed on the same scale, or that a predator can't affect prey unless it occurs at a similar density? "
To the layman that graph is very convincing , but with no quantifying legend ( apart from time ) how do you expect it to be understood correctly. Its basic stats a graph has to have a X and Y legend or it is open to different interpretations .
CJ Bell quote “Just so we're all clear that's the UNIVERSITY OF EAST ANGLIA folks, tuition fees £3,750 p.a.” Just what has that to do with the subject in hand.
While I was there the UEA was nationally recognised as one of the top universities to study ecology in the country bettered only by Oxford and Cambridge. That did not stop those universities offering lecturing jobs to several of the UEAs lecturers. It’s a very juvenile statement you have made not worthy of a schoolboy let alone someone who is supposed to be mature.
One of the major objectives I always imparted into my students was to question everything you read or I taught and form a balanced opinion of their own , not to go blindly on with a closed mind. It’s a lesson some others would do well to follow.
You have some good points , but not enough to prove your case. These are to many other variables in play that could be affecting house sparrows decline and you seem to claim that if the evidence is not available other causes cannot counted. If the evidence is not available , then before making such possibly damaging claims that could result in sparrowhawk control go and do the work yourself. Come back with a balanced paper with all the other variables explored , then make your claims. Exploration of stats and population models is only half the job and needs to be supported with hard field work. And you wondered why the paper rejected your work !
In short Job only half done. Well I have to get on with my own data inputs now from a day in the field with wild geese!
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The link I provided is to the publication page on my website. There you will see a list of article titles, with the relevant paper at the very top. Beside each title is a ‘download’ link. If you click on this link, a pdf copy of the paper will appear on your computer screen. I regret the difficulty of this procedure, but I had assumed that it is widely understood, even at ‘leading universities’.
What evidence do you adduce that spilled grain was a limiting factor for the seed eaters on your study plots? Did you instruct your students to erect hypotheses, derive improbable predictions, and carry out critical tests? How did they do so in this case?
I would be intrigued to see you devise a protocol to quantify the amount of corn-based garbage in urban areas, and then establish its role as a limiting factor for sparrow populations. It would seem urgent that this be done if, as you say, we are not otherwise permitted to draw any inferences about the cause of population decline.
I seem to have achieved the feat of being convincing and incomprehensible at the same time. However I doubt whether the plot would deceive anyone capable of distinguishing a webpage from a scientific paper. In what way do you think the plot could mislead?
I don’t know, but since you brought it up I’m sure it must have something to do with it.
And did you impart an understanding that it’s unwise to impute a closed mind to another party on the basis that their opinion differs from yours, even when you’ve read the paper on which their opinion is based?
Do you believe that if an explanatory variable explains every detail of variation in a process across an extended period of time and a wide area, and if the explanatory power is equally evident at a variety of temporal and spatial scales, and if the process linking the explanatory variable with the process is readily understood, that inference of a connection between the variable and the process remains illegitimate unless every other conceivable variable has been quantified and eliminated?
http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
Your links are still not working so perhaps your system is not compatible with my server.
CJ BELL quote “What evidence do you adduce that spilled grain was a limiting factor for the seed eaters on your study plots? Did you instruct your students to erect hypotheses, derive improbable predictions, and carry out critical tests? How did they do so in this case? “
Now here you show your inexperience. Forget collected data for a moment. 30 – 40 years ago you could walk into many farm barns and see uncovered corn spilled on the barn floor. Tons of it. Large flocks could be seen with the naked eye flying into open windows \ doors and feeding on the grain. Now visit a modern farm grain store . Birds are no longer allowed access to it.
You do not need to see data to see the difference. Ask any forum member over 50 who used to visit farms and they will tell you the same story , but because nobody counted the birds , grain loss or dropping spoiling of the corn you seem incapable of accepting this.
Maybe I am wrong and the birds just went in there to watch the mice play !!!!!!!!!
Perhaps I could put this another way. Put 100 sparrows in a cage with ample food for a few weeks and then remove 1\2 the food . It would be reasonable to assume the removal of the food will effect the birds in some way. Very artificial I know , but it gives a taster of what has happened in the countryside.
Talk about a close mind. It’s a real world out there and everything is not quantified.
CJ Bell quote “I would be intrigued to see you devise a protocol to quantify the amount of corn-based garbage in urban areas, and then establish its role as a limiting factor for sparrow populations. It would seem urgent that this be done if, as you say, we are not otherwise permitted to draw any inferences about the cause of population decline.
I would have thought that would be very easy for anyone with the practical skills of a well trained ecologist. I would have expected any of my 1st year students to do it , but it does mean going out into the real world away from computers and looking for yourself. Picking over the types of “ urban waste “ and seeing what percentage the sparrows eat , OOOOO you could even do a calorific breakdown. Then would have the basis to form some data.
Where have I said that we cant draw any inferences about the cause of population decline. In fact I have been saying the opposite we need to look at all factors involved.
CJ Bell quote “I seem to have achieved the feat of being convincing and incomprehensible at the same time. However I doubt whether the plot would deceive anyone capable of distinguishing a web page from a scientific paper. In what way do you think the plot could mislead?
Any graph without clear labelling is open to individual interruption. That’s basic maths any schoolboy knows. . You have fallen into the trap of so many before you. You know what you mean , and assume everyone else knows what you mean too. .
CJ Bell quote “I don’t know, but since you brought it up I’m sure it must have something to do with it.”
Read your own post. I did not bring up the subject of university fees , you did.
CJ Bell quote “Do you believe that if an explanatory variable explains every detail of variation in a process across an extended period of time and a wide area, and if the explanatory power is equally evident at a variety of temporal and spatial scales, and if the process linking the explanatory variable with the process is readily understood, that inference of a connection between the variable and the process remains illegitimate unless every other conceivable variable has been quantified and eliminated? “
I have several problems with that statement .
1. explanatory variable explains every detail of variation in a process across an extended period of time and a wide area.
NO. This only covers the details you have included. It is very unlikely that every variable over a extended period of time will have been quantified or perhaps even known.
2. explanatory power is equally evident at a variety of temporal and spatial scales, and if the process linking the explanatory variable with the process is readily understood
This is very subjective as it depends on the number of time linked spatial scales to provide a reliable answer and only if the researcher had approached the data in an unbiased manner .
3. other conceivable variable has been quantified and eliminated?
In ecology its almost impossible to quantify every variable , we work on probability and the higher percentage of probability the more likely our conclusions are correct.
Our senior lecture now a fellow in Cambridge university used to have a similar extract posted up outside his office and stated if anyone produced such wording their work would be down marked . It clearly shows the way your mind works in an abstract from the real world. Science has to be understood by everyone if it is to have any value in society not a snobbish minority or it has no value. For gods sake look up from your computer models and PC screen and see there is a real world out there.
As I have said already you have got some possible answers to the problem of declining sparrows . but until all other factors are covered its not the whole answer.
CJ BELL quote “What evidence do you adduce that spilled grain was a limiting factor for the seed eaters on your study plots? Did you instruct your students to erect hypotheses, derive improbable predictions, and carry out critical tests? How did they do so in this case? “
Now here you show your inexperience. Forget collected data for a moment. 30 – 40 years ago you could walk into many farm barns and see uncovered corn spilled on the barn floor. Tons of it. Large flocks could be seen with the naked eye flying into open windows \ doors and feeding on the grain. Now visit a modern farm grain store . Birds are no longer allowed access to it.
You do not need to see data to see the difference. Ask any forum member over 50 who used to visit farms and they will tell you the same story , but because nobody counted the birds , grain loss or dropping spoiling of the corn you seem incapable of accepting this.
Maybe I am wrong and the birds just went in there to watch the mice play !!!!!!!!!
Perhaps I could put this another way. Put 100 sparrows in a cage with ample food for a few weeks and then remove 1\2 the food . It would be reasonable to assume the removal of the food will effect the birds in some way. Very artificial I know , but it gives a taster of what has happened in the countryside.
Talk about a close mind. It’s a real world out there and everything is not quantified.
CJ Bell quote “I would be intrigued to see you devise a protocol to quantify the amount of corn-based garbage in urban areas, and then establish its role as a limiting factor for sparrow populations. It would seem urgent that this be done if, as you say, we are not otherwise permitted to draw any inferences about the cause of population decline.
I would have thought that would be very easy for anyone with the practical skills of a well trained ecologist. I would have expected any of my 1st year students to do it , but it does mean going out into the real world away from computers and looking for yourself. Picking over the types of “ urban waste “ and seeing what percentage the sparrows eat , OOOOO you could even do a calorific breakdown. Then would have the basis to form some data.
Where have I said that we cant draw any inferences about the cause of population decline. In fact I have been saying the opposite we need to look at all factors involved.
CJ Bell quote “I seem to have achieved the feat of being convincing and incomprehensible at the same time. However I doubt whether the plot would deceive anyone capable of distinguishing a web page from a scientific paper. In what way do you think the plot could mislead?
Any graph without clear labelling is open to individual interruption. That’s basic maths any schoolboy knows. . You have fallen into the trap of so many before you. You know what you mean , and assume everyone else knows what you mean too. .
CJ Bell quote “I don’t know, but since you brought it up I’m sure it must have something to do with it.”
Read your own post. I did not bring up the subject of university fees , you did.
CJ Bell quote “Do you believe that if an explanatory variable explains every detail of variation in a process across an extended period of time and a wide area, and if the explanatory power is equally evident at a variety of temporal and spatial scales, and if the process linking the explanatory variable with the process is readily understood, that inference of a connection between the variable and the process remains illegitimate unless every other conceivable variable has been quantified and eliminated? “
I have several problems with that statement .
1. explanatory variable explains every detail of variation in a process across an extended period of time and a wide area.
NO. This only covers the details you have included. It is very unlikely that every variable over a extended period of time will have been quantified or perhaps even known.
2. explanatory power is equally evident at a variety of temporal and spatial scales, and if the process linking the explanatory variable with the process is readily understood
This is very subjective as it depends on the number of time linked spatial scales to provide a reliable answer and only if the researcher had approached the data in an unbiased manner .
3. other conceivable variable has been quantified and eliminated?
In ecology its almost impossible to quantify every variable , we work on probability and the higher percentage of probability the more likely our conclusions are correct.
Our senior lecture now a fellow in Cambridge university used to have a similar extract posted up outside his office and stated if anyone produced such wording their work would be down marked . It clearly shows the way your mind works in an abstract from the real world. Science has to be understood by everyone if it is to have any value in society not a snobbish minority or it has no value. For gods sake look up from your computer models and PC screen and see there is a real world out there.
As I have said already you have got some possible answers to the problem of declining sparrows . but until all other factors are covered its not the whole answer.
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Nature__lover
Well-known member
I think it has more to do with the industrialisation of the landscape which reduces invertebrate numbers and therefore house sparrow numbers. Obviously, House sparrows are well adapted to living in cities and towns, but a lot of people think of them as pests because of that fact and actively discourage them, rather than accepting the fact they have been pushed into more industrialised because their natural environment is gradually dwindling. I also think the neatening of gardens has contributed a lot- they need deep undergrowth and thick, flourishing hedgerows- not perfectly trimmed ornamental hedges and concrete patios . but of course, we'll never be able to pinpoint the exact reason for their decline, because it will be a mixture of things. but natural predators should not be decided as the reason.
everyone just needs to stick together and do all they can to help the House sparrows!
putting up communal nestboxes and leaving your garden a little wilder could really help.
Amy
everyone just needs to stick together and do all they can to help the House sparrows!
putting up communal nestboxes and leaving your garden a little wilder could really help.
Amy
AnotherNightOwl
Registered Guest
Frenchy
Well-known member
I was talking to an old Lincs farmer the other week while doing Atlas work. The inevitable subject of Magpies came up, and while we were happily and constructively debating the issue, he said that back when he was a young man (presumably the 1950's) there were thousands of sparrows on his farm (nr Skegness). In fact, there were so many they were like a plague. He then slipped up by saying that in one day alone he had deliberately poisoned 1000 sparrows. When i pointed out the slight correlation with the decline of sparrows on his land and him killing them all, he went a bit quiet.
One more factor to throw in the mix, even given an exaggeration on his part!
One more factor to throw in the mix, even given an exaggeration on his part!
It wouldn't be reasonable to make such an assumption. If food availability is ‘ample’ at the beginning of the experiment, it may still be after it has been halved, and even if it is halved again. The birds will only be affected if food is reduced below the threshold of ‘ampleness’. This is why nothing can be inferred from a correlation between a decline in a measure of food abundance and that of a consumer population.
That would be the real world in which you can walk onto anyone’s property and start poking around in their rubbish any time you want, would it?
I recommend you re-read the sentence, and concentrate hard on the qualifier ‘otherwise’. I also doubt you really mean ‘all factors involved’. Studies of bird declines tend to invest much treasure in investigating agricultural variables, while blithely ignoring predation.
Er.. yeah, I think we know what you mean, but what I asked you was how you think the plot could mislead.
“Yes” would have been more concise.
I’m afraid you’ve lost me here. What wording am I getting low marks for? I need to know so I can pass on the admonishment to my senior Cambridge lecturer co-author.
You sure got me there. I’m a real Ivory Tower guy – never try to explain my work to anybody, and never done a day of fieldwork in my life.
http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
CJ Bell quote “It wouldn't be reasonable to make such an assumption. If food availability is ‘ample’ at the beginning of the experiment, it may still be after it has been halved, and even if it is halved again. The birds will only be affected if food is reduced below the threshold of ‘ampleness’. This is why nothing can be inferred from a correlation between a decline in a measure of food abundance and that of a consumer population.”
If you have never tried it how do you know that ? Guess work I suppose !!!
CJ Bell quote “That would be the real world in which you can walk onto anyone’s property and start poking around in their rubbish any time you want, would it? “
I see no problem with that at all. When ringing I have often asked householders if we could use their garden to catch birds and never been refused yet. If they are happy to let someone ring I am sure there would be no objections to surveying their rubbish , but the majority of urban waste that is going to be of any interest to house sparrows is likely to be in public areas , parks , rubbish tips , outside fast food outlets ect, as not many people leave waste laying in their garden . Its in bins out of reach of the birds.
CJ Bell quote “Er.. yeah, I think we know what you mean, but what I asked you was how you think the plot could mislead.”
Guess .. maybe the words “Any graph without clear labelling “ is a hint.
CJ Bell quote “Yes” would have been more concise.”
I did not say yes because it would not be sufficient for your question and open to misinterpretation.
Finally can you really say that last statement was written in a manner the majority of people can clearly understand. Science that only a few elite can understand is not good for the future of research and that last question clearly falls into that box. I doubt more that a hand full of people on this form without a lot of thought would understand it.
As for marks , the mere fact that any of this work is open to question and indeed is being questioned or even disbelieved by some of the people who have posted on the topic indicates that the work is not of the highest standard. To acheve a high standard a students work needs to be watertight. If you had admitted that it only covers one aspect of the possible cause of house sparrow decline , then fine , but by dismissing any other causes merely because the data is not available it discredits the conclusions of the report.
You make assumptions that house sparrows would be vulnerable to predation to the returning sparrowhawks because they had lost the need to be wary of them. My experience is that predator avoidance can be reduced , but regained very quickly.
To give an example of this. Common buzzards are a recent coloniser to my area . Our first birds turned up in my wood 15 years ago and when one entered a wood all the wood pigeons fled as they would any large raptor. Over the following years they learned buzzards were not a serious threat and on a number of occasions would feed on the same stubble as up to 3 buzzards were hovering above hunting voles. Last year a pair of goshawks arrived in the wood and within a couple of weeks the pigeons fled at the sight of any large raptor including common buzzards. In this case predator avoidance was learnt within 2 weeks. Is there any reason why house sparrows , a bird with quick learning ability should not learn hawk avoidance just as quickly.
So if any of my students had made similar claims they would have lost marks on that one statement alone unless they could produce work to back it.
Good quality science comes from strong unshakable facts laid out in a manner that indicates the subject has been thoroughly investigated and is understood by most people with a reasonable education. Clearly the topic of this paper has only looked at one aspect of house sparrow decline , choosing to ignore other possible factors as I have said , it has some good points , but job is only half done .
And a job only half done is very risky when it could be used by those that want a cull of sparrowhawks.
Ps its great that you have done some fieldwork on other topics , Thats not in question , but how many observations in the field did you do on house sparrow - sparrowhawk interactions to back some off the claims you have made.
If you have never tried it how do you know that ? Guess work I suppose !!!
CJ Bell quote “That would be the real world in which you can walk onto anyone’s property and start poking around in their rubbish any time you want, would it? “
I see no problem with that at all. When ringing I have often asked householders if we could use their garden to catch birds and never been refused yet. If they are happy to let someone ring I am sure there would be no objections to surveying their rubbish , but the majority of urban waste that is going to be of any interest to house sparrows is likely to be in public areas , parks , rubbish tips , outside fast food outlets ect, as not many people leave waste laying in their garden . Its in bins out of reach of the birds.
CJ Bell quote “Er.. yeah, I think we know what you mean, but what I asked you was how you think the plot could mislead.”
Guess .. maybe the words “Any graph without clear labelling “ is a hint.
CJ Bell quote “Yes” would have been more concise.”
I did not say yes because it would not be sufficient for your question and open to misinterpretation.
Finally can you really say that last statement was written in a manner the majority of people can clearly understand. Science that only a few elite can understand is not good for the future of research and that last question clearly falls into that box. I doubt more that a hand full of people on this form without a lot of thought would understand it.
As for marks , the mere fact that any of this work is open to question and indeed is being questioned or even disbelieved by some of the people who have posted on the topic indicates that the work is not of the highest standard. To acheve a high standard a students work needs to be watertight. If you had admitted that it only covers one aspect of the possible cause of house sparrow decline , then fine , but by dismissing any other causes merely because the data is not available it discredits the conclusions of the report.
You make assumptions that house sparrows would be vulnerable to predation to the returning sparrowhawks because they had lost the need to be wary of them. My experience is that predator avoidance can be reduced , but regained very quickly.
To give an example of this. Common buzzards are a recent coloniser to my area . Our first birds turned up in my wood 15 years ago and when one entered a wood all the wood pigeons fled as they would any large raptor. Over the following years they learned buzzards were not a serious threat and on a number of occasions would feed on the same stubble as up to 3 buzzards were hovering above hunting voles. Last year a pair of goshawks arrived in the wood and within a couple of weeks the pigeons fled at the sight of any large raptor including common buzzards. In this case predator avoidance was learnt within 2 weeks. Is there any reason why house sparrows , a bird with quick learning ability should not learn hawk avoidance just as quickly.
So if any of my students had made similar claims they would have lost marks on that one statement alone unless they could produce work to back it.
Good quality science comes from strong unshakable facts laid out in a manner that indicates the subject has been thoroughly investigated and is understood by most people with a reasonable education. Clearly the topic of this paper has only looked at one aspect of house sparrow decline , choosing to ignore other possible factors as I have said , it has some good points , but job is only half done .
And a job only half done is very risky when it could be used by those that want a cull of sparrowhawks.
Ps its great that you have done some fieldwork on other topics , Thats not in question , but how many observations in the field did you do on house sparrow - sparrowhawk interactions to back some off the claims you have made.
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No, the thing that eludes you in virtually every comment you make, which is logic. Consider the argument implicit in this statement:
How do you know starvation has caused seed-eaters to decline?
Because seeds have declined.
How do you know seeds have declined below the starvation threshold?
Because seed-eaters have declined
How do you know starvation has caused seed-eaters to decline?
This is known as a circular argument. No guesswork is required to see that it doesn’t make sense.
So sparrows only feed where it’s easy to sample? It’s reassuring to know you taught your students the importance of randomisation. Do you think it might also be interesting to sample garbage in cities where sparrows haven’t declined? There must still be plenty of corn-based litter in those places according to your reasoning – but why do you suppose that is?
OK, I’ll give this one last try. What mistaken conclusion might it be possible to draw from the graph as it’s currently presented?
Forgive me if I don’t join you in condemning the science I don’t understand. I don’t really want to eat dirt and live in a hole in the ground thank you very much. So far as my question (not statement) is concerned, I suspect it only eludes members of a few special needs groups. Senior RSPB & BTO staff and ecology lecturers at leading universities spring to mind.
Did you ever give your students low marks for rambling responses that are irrelevant to the question I wonder? If the work is so shoddy how did it get through peer review?
Yes there is, and it’s set out in the paper. Have you read the paper yet, by the way?
The study leading to the article developed out of a House Sparrow nest box and colour ringing scheme that I devised and implemented personally, during which I spent many hours watching interactions with Sparrowhawks. Nice of you to ask, but I fear the horse has bolted.
http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
AnotherNightOwl
Registered Guest
Jeez, this thread has turned into a bloody tennis match! :-O
Deuce .....
Deuce .....
Jane Turner
Well-known member
As far as was aware, it was already game set and match, just someone hasn't noticed
Yep, it's called debate. Disturbing I know, but there are plenty of other threads where you can bask in smug groupthink and mutual backslapping. Here's something to soothe troubled minds:
It's the wicked farmer, this I know
For the RSPB tells me so..
For a topic that focusses on a very UK-based issue, one could also ask if this study was so good why it ended up in an American-based journal, rather than any of the respected UK journals.
Not good enough to get through UK peer reviews? Reviewers far afield might conveniently be less aware of failings in your data, such as urbanisation and bird data quality realting to the UK, etc.
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AnotherNightOwl
Registered Guest
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