Who To Believe? (4 Viewers)

[David Bryant]

Sorry Tim! You're quite right about Darwin!
Is this 'Krebs' the one from the cycle? If so, what a gifted geezer!
The gull is some sort of Yellow-legged job, but I never have time to stop and grill it!
ATB!
David

 

[Rhion]

Why are there no Black Kites flying freely around the U.K. and why are only captive bred Red Kites, and their siblings flying around in the U.K.

The Red Kites in Wales are wild, and we were still part of the U.K. last time I looked. Unfortunately - but that's another story :C

 

[Anthony Morton]

...and Anthony's quote of Ian Peter's post doesn't make any sense to me at all. I'm baffled as to the meaning of it, and if read at face value it seems irrelevant and not related to Stevie Evens post at all. To have any effect on numbers it is necessary to remove all predators is so odd I wouldn't know where to start in repying!!!

Tim,

I am not looking to start another literary punch-up, as Keith and others have correctly surmised. My concern is that there appears to be two conflicting answers here, so which one is correct - or are they both perhaps wrong as I believe you may have suggested earlier?

I'm also sorry if my short precis of Ian's posting #193 on the 'Hunting -v- Birdwatching' thread has confused the issue. Perhaps if it is read in full against StevieEvans Postings #117 and 179 the situation will become clearer, as hopefully will my reason for starting this thread.

Anthony

 

[Edward woodwood]

"until then the accepted science is as Mike P and Jos pointed out."



To who, the blinkered, the un-questioning, the pack followers, actually WHO accepts this "science".

This argument is reductionist to the point of absurdity. If you start to deny what the vast majority of scientists accept, just where are we? There will never be any end to this 'debate'.

I can't begin to answer the 101 questions in your post Malky. If you seriously believe those ideas you need to do some studies and publish them and convince people.

atb
Tim

 

[Jane Turner]

Sorry Tim! You're quite right about Darwin!
Is this 'Krebs' the one from the cycle? David

No sorry.. Krebs from the Krebs Cycle was a refugee from Nazi Germany who did his work in the UK... the Krebs of Ecology fame was/is Charles.... I had to dig through all sprts of old books to find that!

 

[GeoffWood]

Books to study

Ecology by Krebs is an old standard
Ecology by Begon, Harper and Townsend likewise

Evolution by Peter Skelton touches on similar areas but is excellent in its own right

An introduction to behavioural ecology by Krebs and Davies is very good as well

May I suggest a look at "Population Ecology of Raptors" by Dr Ian Newton (Poyser) Ian Newton is a professionally qualified ecologist.
OK before anyone corrects me, I know that Magpies are not "raptors" but as predators, there will be a lot of relevant comparisons along with scientific data.

 

[Anthony Morton]

If You Want Songbirds, Kill Magpies.

Another thread of deliberately obtuse cod-science. Having tried all the other debates we're now left with the old Magpie/songbird argument.

It has been proved time and time again that Magpie density does not affect the number of songbirds which survive to the the following year. Yes, they eat songbirds, but they are the birds that would have died anyway - if very Great Tit chick survived the winter we'd be swamped in the things by now.

Obtuse cod-science? That's rather dismissive and not a little patronising, isn't it? I freely admit that I'm only a foot-soldier when it comes to the scientific side of birding, so I'll leave others to pick the bones out of what follows. Please note, however, that these are NOT my words - they are extracts from an interesting article published in the April 2002 edition of THE FIELD magazine under the title: 'If You Want Songbirds, Kill Magpies' based on the scientific paper referred to below and which was published in the Journal Of Applied Ecology.

Quote ...'Biologists from the British Trust for Ornithology (BTO) and the University of East Anglia, who are the authors of "Large-scale spatial variation in the breeding performance of song thrushes (Turdus philomelos) and blackbirds (T merula) in Britain", conclude: 'Nest failure rate during incubation increased significantly where corvids were more abundant, suggesting a role for avian nest predators in determining spatial variation in reproductive output." This might seem like common sense to anyone connected with game management but for many years it has been vigorously denied by bird protectionists.

'The Game Conservancy Trust comments that the result "comes as somewhat of a surprise, since the BTO and the RSPB have loudly proclaimed a 'not guilty' verdict for these corvids in relation to songbird declines. At Loddington we have seen a spectacular increase in song thrush breeding density which followed hard on the heels of improved nesting success brought about by crow and magpie control."

'The recent BTO study has the virtue of being extremely thorough and founded on a huge database: the nest records collected by thousands of amateur bird-watchers since the Thirties. A sample of this information, covering about 6,000 nests, was put alongside more than a dozen factors that might influence breeding success, from altitude and landscape to latitude and spring temperature.

'One of the most influential factors turned out to be the frequency occurrence of corvids. This study is serious science and it has produced an outcome that even the authors themselves may not have foreseen: predation is crucial.

'The biologists reached the conclusion after excluding carrion crows from their calculations; "Recent studies suggest that most predation is from smaller corvids, particularly magpies."

'The paper's authors are Emmanuel Paradis, Stephen R. Baillie, William J. Sutherland, Richard D. Gregory, Caroline Dudley and Humphrey Q. Crick and their study of large-scale ecological patterns is concentrated on the thrush and blackbird.' Unquote

Anthony

 

[James]

"Truth is a function of time."

Albert Einstein

 

[Nightranger]

Which one is correct?

Hi Anthony,

Essentially, both are correct. My post reflected the national situation whereas there is no doubt that short-term results can be achieved with local controls. All the same, experience shows us that this has a tendency to also cause an imbalance that gives advantage to the species that react quickest. A good example is our friend the great spotted woodpecker, which are predators in their own right. They are not top of the food chain though and removing the predators leads to an advantage for these birds and though the smaller birds will be OK for the first year or so, they will certainly experience difficulties later. Remember that woodpeckers are much more systematic than magpies particularly with tree-nesting birds.

Ian

 

[Jane Turner]

Hi Anthony,

Essentially, both are correct. My post reflected the national situation whereas there is no doubt that short-term results can be achieved with local controls. All the same, experience shows us that this has a tendency to also cause an imbalance that gives advantage to the species that react quickest. A good example is our friend the great spotted woodpecker, which are predators in their own right. They are not top of the food chain though and removing the predators leads to an advantage for these birds and though the smaller birds will be OK for the first year or so, they will certainly experience difficulties later. Remember that woodpeckers are much more systematic than magpies particularly with tree-nesting birds.

Ian

....plus there is plenty of evidence to say that locally the temporary increase in survival rate is quickly counter-balanced by increased competition for food etc.. so that any gains are cancelled out by the next breeding season.

 

[James]

Darwinian Evolution is VERY much under scrutiny at the mo! (viz the case of the Sticky Squid! A Darwinian impossibility!) You'd've been better using The Moon Landings as an example! LOL![/QUOTE]

Can you point me at more info on this squid and why it is an impossibility?

Cheers

James :h?:

 

[Nightranger]

""It has been proved time and time again that Magpie density does not affect the number of songbirds which survive to the following year. "Yes, they eat songbirds, but they are the birds that would have died anyway""

How does one qualify that statement, "but they are birds that would have died anyway".

Malky

Hi Malky,

The phrase is perfectly accurate because it is little realised that all bird populations are calculated on the basis of nest sites. We know how many young birds are produced each year and we know the population trends. Predation is not separately considered, it is merely a component of the overall mortality. Let me see if I can explain in hypothetical terms:

If population in pairs = X we can produce a number of scenarios because X also = population as used by BB, BTO, WWT, RSPB etc. Take the robin for instance.

X pairs produce 4 x 3 x X young where 4 is the average brood and three the number of broods (blue tits it would be 6 x 1 x X). For a stable population, we are always left with X. Robins are generally stable if not, increasing slightly so we can put some flesh on the equation. 4,200,000 pars x 4 x 3 = 50,400,000 young per year. If we look at the ratios, then young tend to outnumber adults by anywhere between 100-50:1 yet we have to get back to the orginal population figure so where do these birds go? 90% of all birds produced in any year will not reach maturity coupled with around 10% mortality of mature adults. The component that dictates declines is a reduction in breeding success and this is usually food or habitat failures whreas increases are dictated by survival rates of adults (mainly through winter). Given that robins and chaffinches are magpie fodder yet have stable populations and blue tits and great tits are increasing, it does not make sense that predation of any kind is causing species declines. However, there is no question that you can get local effects by removing predators. The habitat is usually at carrying capacity anyway so all this is likely to achieve is a temporary build up of young birds surviving into autumn. There will be insufficient resources to support these birds through winter anyway but the main issue would be the natural spacing in spring and this would not change irrespective of the presence of predators. Robins are a good example because their territories are fixed and there simply is no space to fit additional territories in. In conclusion, I can guarantee that anyone removing magpies during the summer will see an improvement in bird numbers, particularly towards the end of summer.

Ian

 

[Richard D]

...THE FIELD magazine under the title: 'If You Want Songbirds, Kill Magpies' based on the scientific paper referred to below and which was published in the Journal Of Applied Ecology.

Quote ...'Biologists from the British Trust for Ornithology (BTO) and the University of East Anglia, who are the authors of "Large-scale spatiasl variation in the breeding performance of song thrushes (Turdus philomelos) and blackbirds (T merula) in Britain", conclude: 'Nest failure rate during incubation increased significantly where corvids were more abundant, suggesting a role for avian nest predators in determining spatial variation in reproductive output." This might seem like common sense to anyone connected with game management but for many years it has been vigorously denied by bird protectionists.

It would be interesting to read the original research rather than a game-shooting's magazines spin on it, as all research suggests that breeding levels are not the reason for the decline in song thrush numbers, rather the survival rate of first year (which would rule out Magpie predation as the cause).

Richard

 

[Nightranger]

It would be interesting to read the original research rather than a game-shooting's magazines spin on it, as all research suggests that breeding levels are not the reason for the decline in song thrush numbers, rather the survival rate of first year (which would rule out Magpie predation as the cause).

Richard

Hi Richard,

I know of one paper covering song thrushes and magpies (I am pretty sure it was not BTO) that used one of the poorest scientific techniques I have ever seen. It took the distribution maps for magpies and song thrushes and overlaid them to see what happened. Presto! The densest populations of magpies coincided with low thrush numbers. Unfortunately, this is totally unhelpful because the densest populations of magpies are in urban areas that are unlikely to support large numbers of thrushes anyway.

Ian

 

[Jane Turner]

Until I was unable to convince the of the futility of it, my local Golf course used a Larsen trap to "control" Magpie populations. I've been covering the patch for 25 years and only observed one a few effects over the period of the cull... which may of course just been coincidental. There was an influx of new Magpies (as determined) by ringing, a increase in the number of Carrion Crows from one to two pairs and fewer pair of breeding Skylarks.

 

[Jane Turner]

Hi Richard,

I know of one paper covering song thrushes and magpies (I am pretty sure it was not BTO) that used one of the poorest scientific techniques I have ever seen. It took the distribution maps for magpies and song thrushes and overlaid them to see what happened. Presto! The densest populations of magpies coincided with low thrush numbers. Unfortunately, this is totally unhelpful because the densest populations of magpies are in urban areas that are unlikely to support large numbers of thrushes anyway.

Ian

Ian, the paper that I think is being refered to shows, somewhat unsurprisingly, that losses of eggs and nestlings of Slackbirds and Song thrushes to Magpies are higher where Magpies are common. As we say round here "No sh!t Sherlock" I don't think it goes as far as to comment on the long term stability of Thrush populations in those areas.

 

[Edward woodwood]

Obtuse cod-science? That's rather dismissive and not a little patronising, isn't it? [/I].

Quote 'The paper's authors are Emmanuel Paradis, Stephen R. Baillie, William J. Sutherland, Richard D. Gregory, Caroline Dudley and Humphrey Q. Crick and their study of large-scale ecological patterns is concentrated on the thrush and blackbird.' Unquote

Anthony

You sound suprised Anthony...?

Bill Sutherland is one of the best ecologists in the world and it's an interesing paper for sure but the picture is so much bigger and more complicated than that.

 

[Anthony Morton]

Hi Richard,

I know of one paper covering song thrushes and magpies (I am pretty sure it was not BTO) that used one of the poorest scientific techniques I have ever seen. It took the distribution maps for magpies and song thrushes and overlaid them to see what happened. Presto! The densest populations of magpies coincided with low thrush numbers. Unfortunately, this is totally unhelpful because the densest populations of magpies are in urban areas that are unlikely to support large numbers of thrushes anyway.

Ian

Hi Ian,

Can I suggest a few options to perhaps resolve this matter and prevent us going round in circles?

1. Do you have any contacts at the BTO or the University of East Anglia who can provide a copy of the original paper 'Large-scale spatial variation in the breeding performance of song thrushes (Turdus philomelos) and blackbirds (T merula) in Britain'?

2. Does the RSPB's own library hold copies of either the paper itself, or theJournal of Applied Ecology it was published in just before April 2002?

3. As I listed the six authors credited with presenting the paper, would it be possible for you to 'pull rank' and ask one of them for a copy?

Anthony

 

[Edward woodwood]

I have contacts at UEA and can get one from Mr Sutherland no doubt

the fact that so much emphasis is put on this ONE study belies a tale in itself.

 

[Nightranger]

Hi Ian,

Can I suggest a few options to perhaps resolve this matter and prevent us going round in circles?

1. Do you have any contacts at the BTO or the University of East Anglia who can provide a copy of the original paper 'Large-scale spatial variation in the breeding performance of song thrushes (Turdus philomelos) and blackbirds (T merula) in Britain'?

2. Does the RSPB's own library hold copies of either the paper itself, or theJournal of Applied Ecology it was published in just before April 2002?

3. As I listed the six authors credited with presenting the paper, would it be possible for you to 'pull rank' and ask one of them for a copy?

Anthony

Hi Anthony,

I am not sure what you are asking here because I did not comment on the paper you quoted, I mentioned the other paper just out of interest. I dare say I can get hold of the paper but I don't really have a professional reason for doing so at this stage. However, if you want me to get a copy of the paper for your use, then I will be delighted to do so but I think it would be better to do this through the PM system. I am currently looking at the Goostrey et al paper on cormorants and I will post this as a separate thread but not for evidence about the cull BTW. I assume if you want me to read this paper that supports one idea then it would be equally appropriate to read anything on the same subject and Tim Birkhead's book gives some excellent references.

Ian