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.
Having now read your paper i feel there are a number of issues that need to be addressed from it.
PS, none of the links you provide on your site can be located on my browser. All say NOT FOUND.
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.
Perhaps I should make clear now I used to lecture in ecology and ornithology at the UEA
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.
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.
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.
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.
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 !
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.
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
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.
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. .
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 .
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.
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 !!!
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.
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.
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.
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.
Jeez, this thread has turned into a bloody tennis match!
If the work is so shoddy how did it get through peer review?
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..