Uk Peregrine Population Limit? (1 Viewer)

[robinm]

Based on your figures, this shows that Sparrowhawks predate the equivalent in weight of 110 million songbirds per annum. Yes, 110 MILLION!

Which is, of course, not the same as 110M actual birds.

 

[CBB]

I nearly missed this - must be getting old. More 'schoolboy howlers' of the mathematical kind I'm afraid.

You suggest the population of Sparrowhawks is 40,100 breeding pairs. Fair enough but haven't you forgotten that there will be a similar number (say 40,000) of unpaired adults and juveniles? This makes the TOTAL UK Sparrowhawk population around 120,000 individual birds.

Ian Newton suggests that the male Sparrowhawk consumes the equivalent of 2 sparrow-sized birds per day, and 3 for the larger female. Then if the number of each sex is roughly the same, the average requirement will be 2.5 sparrow-sized birds for each Sparrowhawk.

If 120,000 Sparrowhawks each predate the equivalent weight of 2.5 sparrow-sized songbirds per day, this equates to 300,000 per day. And 300,000 per day x 365 = 109,500 million sparrow-sized birds consumed in a year. As you say, according to the H&OT, songbirds make up between 90% - 98% of the Sparrowhawks' prey requirements.

Based on your figures, this shows that Sparrowhawks predate the equivalent in weight of 110 million songbirds per annum. Yes, 110 MILLION!

Surely this figure is ludicrous! On these figures we appear to be heading towards Sprawk Armageddon. On a similar note, the farmer has just ploughed his fields behind my house and the local kestrel is picking off the mice at free will. Should I be worried about Leicestershire's mouse population or will nature balance this out like it does with most things Come on AM, try and be sensible please.

 

[Edward woodwood]

I don't believe there's a healthy songbird population in UK

Certainly the 'unnatural' landscape (large fields, fewer hedges, insects) leads to the songbird populations being a lot lower than they ought to be. Could sprawks etc keep the population lower than it would otherwise be?. I mean are they having a proportionally greater effect than they 'normally' would in a healthy countryside? Is the sprawk - songbird dynamic cycling at a lower than natural (all things being equal) level?

Probably not but just a thought. I don't believe absolute numbers are that important but processes and the pressures on them certainly are?

Tim

 

[Edward woodwood]

another point

nature doesn't always 'balance' things out - not in such altered environments...

 

[CBB]

Hi Tim,
I was always under the impression that there will be an equilibrium. Do you mean that in an artificial environment, the equilibrium can change?

 

[Edward woodwood]

yes

my friend Dave has just updated the important cote / sutherland paper abstract. Worth getting hold of a copy

A meta-analysis of 20 published studies of predator removal programmes was undertaken to access the effectiveness of predator removal as a conservation measure (Côté & Sutherland 1997). Removing predators had a large, positive effect on hatching success of the target bird species, with removal areas showing higher hatching success, on average, than 75% of the control areas. Similarly, predator removal significantly increased post-breeding population sizes (i.e. autumn densities) of the target bird species. However, the effect of predator removal on breeding population sizes was not significant with studies differing widely in their reported effects. Whilst predator removal often fulfilled the goal of game management, i.e. to boost harvestable post-breeding populations, it was much less consistent in achieving the usual aim of conservation managers, i.e. to maintain and, where appropriate, increase bird breeding population sizes. This may be due to inherent avian population regulation, but also to ineffective predator removal and inadequate subsequent monitoring of the bird populations.

 

[CBB]

Cheers Tim,
Lots of food for thought there. Is the full report available on the web do you know? Wouldn't mind reading it.


Thanks

Chris

 

[nirofo]

I don't believe there's a healthy songbird population in UK

Certainly the 'unnatural' landscape (large fields, fewer hedges, insects) leads to the songbird populations being a lot lower than they ought to be. Could sprawks etc keep the population lower than it would otherwise be?. I mean are they having a proportionally greater effect than they 'normally' would in a healthy countryside? Is the sprawk - songbird dynamic cycling at a lower than natural (all things being equal) level?

Probably not but just a thought. I don't believe absolute numbers are that important but processes and the pressures on them certainly are?

Tim

Hi Tim

I see we are back where this all started a couple of years ago on the Sparrowhawk thread, it was pointed out then and eventually accepted by the majority, that in order for the Sparrowhawk population to remain healthy and survive, there had to be an equally healthy and surviving population of prey species available. Now, unless something has radically changed the status quo in the last couple of years, then I would suggest there's no point in going back over old ground. The fact remains without a healthy population of songbirds etc, then there can be no Sparrowhawks, full stop!!! If the Sparrowhawk population is increasing then so must the songbirds etc.

_____________________


Hi Anthony Morton

By the way , still waiting for your replies to the questions posed to you in earlier posts?

nirofo.

 

[nirofo]

Quote: Anthony Morton, post 518.

"250,000 x 365 = 9.2 million? Shouldn't the total be 91.25 million songbirds predated by hawks in a year?"

Ok, your sums are not wrong, what is wrong however is your failure to understand the breeding dynamics of songbird populations. You quote a figure of 91 million songbirds predated per year, lets assume that 30 million of these birds would have been breeding pairs, now, most songbird pairs will rear a brood of say 4 young to fledging, that's an estimated 120 million young songbirds per year! If we now add to the total of young songbirds the original 91 million adults, we have a total of 211 million songbirds. Quite a healthy population from what is only a small representative total of the number of songbirds in the whole of the UK.

Sparrowhawks and any other bird of prey for that matter are not designed to decimate their food supply to such an extent that they no longer have enough to survive on. Who are we to judge anyway, we farm and kill Chickens, Pheasants, Duck, Geese, Pigs, Cows, Sheep etc., we do this to feed ourselves and survive. Sparrowhawks can't enter into the farming industry very easily, so, they have to hunt wild prey to survive, they need to, we don't!!

nirofo.

 

[Edward woodwood]

Hi

CBB, I think you may be abe to get the paper on line - it's certainly referred to ina nother thread. I might have an electronic copy somewhere

As you might imagine, and the paper hints at (and Bill Sutherland is one of the top ecologists in the world), the reality is more complex than either side on here would have you believe.

Tim

 

[Jos Stratford]

That's EXACTLY what it was, a factual statement whose only intention was to inform the wider audience.

Absolute rubbish - if the only intention was to inform a wider audience, why then the slogan 'save our songbirds' - inform is to give information, ie the figure regarding the number of birds predated. The slogan is propoganda, trying to sway others into the mistaken belief that there is a problem.


Did wonder about your reading and comprehension skills a little earlier Anthony (remember, the post you thought rude) - but if you read that sticker as a simple little desire to pass over a fact about rates of predation and nothing more, then I think it's time for you to restart primary school!

 

[Anthony Morton]

Absolute rubbish - if the only intention was to inform a wider audience, why then the slogan 'save our songbirds' - inform is to give information, ie the figure regarding the number of birds predated. The slogan is propoganda, trying to sway others into the mistaken belief that there is a problem.

Once again you appear to be seeking to deny others the right to hold any opinion which differs with your own. Despite this, do you wish to either accept or contradict the (now outdated) statistical information on songbird predation shown on the sticker?

Did wonder about your reading and comprehension skills a little earlier Anthony (remember, the post you thought rude) - but if you read that sticker as a simple little desire to pass over a fact about rates of predation and nothing more, then I think it's time for you to restart primary school!

Yes indeed, although rudeness does seem to be the preferred defensive tactic of several members on this forum when put on the spot. The expression 'Sticks and stones ...' also springs to mind.

BTW, I can do 'rude' if necessary and some here might even be amazed at how many ways I know to spell PRAT!

 

[Anthony Morton]

Ok, your sums are not wrong, what is wrong however is your failure to understand the breeding dynamics of songbird populations. You quote a figure of 91 million songbirds predated per year, lets assume that 30 million of these birds would have been breeding pairs, now, most songbird pairs will rear a brood of say 4 young to fledging, that's an estimated 120 million young songbirds per year! If we now add to the total of young songbirds the original 91 million adults, we have a total of 211 million songbirds. Quite a healthy population from what is only a small representative total of the number of songbirds in the whole of the UK.

Where this argument is flawed is in the unknown potential number of young birds lost either at the egg or nestling stage because one or even both parents are taken by a Sparrowhawk. Let's assume a pair of Blackbirds go to nest and hatch five young. The Sparrowhawk takes one of the parents and the other continues to rear the youngsters until it too is predated. How many Blackbirds died? In your theory it is only TWO but in practice it was SEVEN, because the five youngsters would all either die of cold or else starve to death, yet they are never included in the true number of birds predated.

Sparrowhawks and any other bird of prey for that matter are not designed to decimate their food supply to such an extent that they no longer have enough to survive on. Who are we to judge anyway, we farm and kill Chickens, Pheasants, Duck, Geese, Pigs, Cows, Sheep etc., we do this to feed ourselves and survive. Sparrowhawks can't enter into the farming industry very easily, so, they have to hunt wild prey to survive, they need to, we don't!!

nirofo.

This ignores one simple and inescapable fact - none of the animals you mention would ever be farmed to a level below a sustainable level, as man is capable of making a judgement on this and preventing it before it happens. Unfortunately predators such as Sparrowhawks are unable to make this same judgement and only see their next meal.

 

[Anthony Morton]

Surely this figure is ludicrous! On these figures we appear to be heading towards Sprawk Armageddon.

The figure was accurate a few years ago but is now higher and still increasing in line with the UK's Sparrowhawk population.

This is NOT the sort of information some bird protection agencies like to have publicised, as it might deter the little old ladies who donate money to supposedly look after the birds

Come on AM, try and be sensible please.

Sensible? Which of us is the one who doesn't seem to have a clue about the current level of Sparrowhawk predation on songbirds in the UK? I'll give you a clue - it's not me!

 

[Jos Stratford]

Once again you appear to be seeking to deny others the right to hold any topic which differs with your own.

I do not wish to deny you the right to hold an opposing opinion - you clearly hold a very different opinion to me on this whole issue and that is your right. What I do have issue with, however, is when certain members try to portray certain deeds as done purely through honest intentions. That sticker, no matter how many times you wish to portray it otherwise, is not a simple gesture by the homing pigeon people to educate the public on dietary requirements of hawks.

Instead of commenting on why this 'information only' gesture also has the loaded 'save our songbirds' alongside, you have chosen to ask me a question about the statistics themselves. Do I regard those statistics as incorrect? None of my posts mentioned this, so not sure why you have chosen to mention it, but I can answer it anyhow.
My answer is two-part:
- first, I have not bothered to go to any reliable references, so I do not know whether they are quoting true figures or not (hence the reason I have not previously responded to this point). However, given the nuber of falsehoods on the RPRA website, I would recommend any interested persons to check for themselves before taking this figure at face value.
- second, the actual figure is rather irrelevant. The sticker, associating the 'save our birds' with the statistics given, clearly wishes to imply there is a problem with the number of birds killed by hawks. I know your opinion differs here, but this is the natural predator-prey thing that you don't wish to accept. There is no point us re-debating this as Jane has given you plenty of information before on this, but sufficient to say, there is not evidence that hawks are causing any reductions whatsoever of bird populations in the UK - many of the most common prey items are increasing and the causes of species in decline have not been linked with any predation.

As regard rudeness, I don't think my posts are particulary rude, but I can apologise to you if they are - my comments on your comprehension skills are purely based on trying to account for why you have problem in understanding basic texts sometimes (did the 'casual' reader test you spoke of some time ago - funny they could see the message behind the sticker and they are not even a birder).

 

[Jos Stratford]

Where this argument is flawed is in the unknown potential number of young birds lost either at the egg or nestling stage because one or even both parents are taken by a Sparrowhawk. Let's assume a pair of Blackbirds go to nest and hatch five young. The Sparrowhawk takes one of the parents and the other continues to rear the youngsters until it too is predated. How many Blackbirds died? In your theory it is only TWO but in practice it was SEVEN, because the five youngsters would all either die of cold or else starve to death, yet they are never included in the true number of birds predated.

Irrelevant, taking your example with Blackbird

Start of breeding season,
Two Blackbirds - two or three broods during the year (10-15 young assuming 5 hatch). So now we have 12-15 birds. Only two will survive to the start of the next season to maintain the stable population. Hawks, cats, food shortages, weather, etc will account for the remainder.

If hawk predation was such a problem, I do wonder how any of these songbirds actually managed to survive into the modern era.

 

[CBB]

The figure was accurate a few years ago but is now higher and still increasing in line with the UK's Sparrowhawk population.

This is NOT the sort of information some bird protection agencies like to have publicised, as it might deter the little old ladies who donate money to supposedly look after the birds



Sensible? Which of us is the one who doesn't seem to have a clue about the current level of Sparrowhawk predation on songbirds in the UK? I'll give you a clue - it's not me!

Hi AM,
Surely the level of predation is irrelevant. It is the effects of predation which should be the focus. There is much literature around, regarding the subject. I'm prepared to read it. You could too. Also you appear to be insinuating that 'some agencies' can have their own agendas. Would this include loaded car stickers from the BHW?


:news:

 

[Jane Turner]

http://www.birdforum.net/showthread.php?t=26754

I'm no going to go to the lengths of refuting AM's riiculous claims again - just read the above thread if you have a need to see what happened last time he stirred this particular pot! All the peer reviewed papers you could wish for are there. Here is just one...


Oh and its amusing to see another thread started by AM with just the same intention!


Proceedings: Biological Sciences
ISSN: 0962-8452 (Paper) 1471-2954 (Online)
Issue: Volume 265, Number 1410 / November 7, 1998

Pages: 2057 - 2062
DOI: 10.1098/rspb.1998.0540
URL: Linking Options
The widespread declines of songbirds in rural Britain do not correlate with the spread of their avian predators

D. L. Thomson, R. E. Green, R. D. Gregory, S. R. Baillie

Abstract:

During the last 30 years, there have been marked declines in the populations of many British songbirds breeding on farmland, while two of their main predators, sparrowhawk (Accipiter nisus) and magpie (Pica pica), have spread back into areas from which they had disappeared. The causes of the songbird declines remain unclear but given the coincidence in timing, it might appear that increased predation could be responsible. Although many studies have failed to find links between changes in the populations of breeding songbirds and mortality from avian predators, previous work has, with few exceptions, involved only short-term studies on small spatial scales. Here we use large-scale, long-term data from a national bird census scheme to examine whether magpies and sparrowhawks could have depressed the rates of year-to-year population change in 23 songbird species. Our results indicate that magpies and sparrowhawks are unlikely to have caused the songbird declines because patterns of year-to-year population change did not differ between sites with and without these predators.

 

[Collster]

The figure was accurate a few years ago but is now higher and still increasing in line with the UK's Sparrowhawk population.

This is NOT the sort of information some bird protection agencies like to have publicised, as it might deter the little old ladies who donate money to supposedly look after the birds



Sensible? Which of us is the one who doesn't seem to have a clue about the current level of Sparrowhawk predation on songbirds in the UK? I'll give you a clue - it's not me!

I thought this thread was about Peregrines, am i to take it that the lack of answers to several questions on that subject means that you have run out of steam. The fact that you have shifted the emphasis to sparrowhawks indicates that you are just after one thing, the right to cull raptors. Give it up Anthony as you are making yourself sound foolish by ignoring the information thats been given to you. You also accuse others of being rude, thats you in a nutshell, you just veil your rudness with a fine command of the English language, still doing it though. Once again i ask, as have others that you kindly address the questions put to you in earlier posts about Peregrines and not wander off to Sparrowhawks just because you haven't got the answers.

 

[Collster]

Where this argument is flawed is in the unknown potential number of young birds lost either at the egg or nestling stage because one or even both parents are taken by a Sparrowhawk. Let's assume a pair of Blackbirds go to nest and hatch five young. The Sparrowhawk takes one of the parents and the other continues to rear the youngsters until it too is predated. How many Blackbirds died? In your theory it is only TWO but in practice it was SEVEN, because the five youngsters would all either die of cold or else starve to death, yet they are never included in the true number of birds predated

Once again you show how little you know about wild birds. As others have pointed out song birds lay several clutches throughout the breeding season, so any calculations you care to make are going to be flawed. To come at it from another angle, Sparrowhawks themselves can be eaten by Goshawk( found two this season) are things like this factored into your equations. No of course not because you think raptors are immune to being eaten, they aint, they suffer at the hands of nature too.