Uk Peregrine Population Limit? (1 Viewer)

[Jane Turner]

Oikos
Volume 104 Page 71 - January 2004
doi:10.1111/j.0030-1299.2004.12814.x
Volume 104 Issue 1


Faced with a choice, sparrowhawks more often attack the more vulnerable prey group
W. Cresswell and J. L. Quinn,

Whether predators always attack the most vulnerable prey or simply attack prey that exceeds a minimum vulnerability level is an important question to answer in furthering our understanding of predator and antipredation behaviour. Predators may attack any reasonably vulnerable prey rather than waste time identifying the most vulnerable prey, particularly when prey can respond quickly to alter their vulnerability in response to a predator. We tested whether sparrowhawks always choose to attack the group of prey that maximises their capture probability, or whether they simply attack any group above a minimum vulnerability. We modelled sparrowhawk attack success when hunting redshanks using data from three winters and found that probability of capture increased when group size or distance to predator-concealing cover decreased. We then used this model to predict the relative vulnerability to capture of redshank groups occurring in pairs in a fourth winter and found that sparrowhawks attacked the most vulnerable prey group twice as often as not (66% n=59 pairs). When sparrowhawks attacked the less vulnerable group, there was no tendency for both groups to be particularly vulnerable or for the difference in the vulnerability between the two groups to be relatively small. This suggests that, while sparrowhawks do on average attack the most vulnerable group available, they consider other factors that affect vulnerability or that additional factors lead them to also attack opportunistically. This suggests that there will be selection for the predator to monitor a large number of prey individuals and groups and for prey to have the ability to monitor the behaviour of conspecifics in the same and different groups so that they can assess relative vulnerability.

 

[London Birder]

my own observations include attacks on birds up front, stragglers and birds seperated from the middle of flocks, and of course on individuals not part of flocks; it's worth ponting out also that many, many stoops and chases are wholly unsuccessful, pigeons are excellent avoiders, often plummeting headlong toward the deck at surprisingly high speeds, I've even seen the odd pigeon actually struggle free when caught ... Peregrines are reasonably opportunistic and in my experience (though I accept not everyones is the same) there are no hard and fast rules or methodolgy utilised in attack.

 

[Jane Turner]

From BWP

Prospective prey spotted at distance, either from circling flight or from elevated vantage-point, e.g. cliff, tree, hill (Baker 1967; Monneret 1973). Pursuit flight follows, finally rising above prey preparatory to rapid stoop (wings folded and held slightly away from body). Estimates of stoop speeds 160–410*km per hr, and at least 240*km*per hr considered feasible (Brown 1976a). Angle of stoop varies with particular circumstances (Glutz von Blotzheim et al. 1971). Unsuccessful stoops frequent: e.g. ♂♂ 83%, ♀♀ 78% (Hantge 1968); of 260 stoops only 7·3% successful (Rudebeck 1953). Suggested that stoops sometimes in play, serious success rate higher (Ratcliffe 1962). Prey usually killed or caught from above in air or struck on ground. Sometimes stoop causes victim to fly up and may then be struck or seized from below (see Glutz von Blotzheim et al. 1971). Occasionally prey caught in air without stoop.


With some species, especially flocking birds, attempts to incapacitate individuals, possibly preferring those with conspicuous traits, e.g. light-coloured plumage, behavioural peculiarity, etc., or obviously weak, injured, or diseased (Eutermoser 1961; Saar 1961; Treleaven 1961; Ratcliffe 1963; Baker 1967; Porter et al. 1973).




Where is your evidence Anthony?

 

[colonelboris]

Wherever I go, in science, reenactment or birding, you always find someone who can pull up references like these in minutes.
Wish I could do that...

 

[Jane Turner]

Wherever I go, in science, reenactment or birding, you always find someone who can pull up references like these in minutes.
Wish I could do that...

Its years of practise refuting some of Anthony's wilder assertions!

 

[Jos Stratford]

Its years of practise refuting some of Anthony's wilder assertions!

Otherwise known as hogwash.

 

[nirofo]

"Time Out!
I see that we are already up to 250 postings on this thread but sadly far too many of them, including some replies, have little or nothing to do with the question I posed at the beginning. It seems that some are only interested in trying to antagonise or belittle other interests they either do not understand, or do not want to understand. Rather than bringing the two sides closer together by examining the common ground, this will only serve to drive them further apart.

So perhaps while we catch our breath we should all read 'Grousemore's' Post #86 again, and in particular the second paragraph which I have highlighted. In the meantime, I will try to answer a few more of the outstanding comments and/or suggestions as and when time allows."

Originally Posted by Grousemore...Certainly not that I've read and I wholly agree with your points about fines; but zealots are on the loose with a 'worthy' cause, so it doesn't matter.

The very worst of Birdforum has been exhibited on this (and a similar) Thread, in that facts and proof are irrelevant when faced with an opportunity to have a go at those whose hobbies we don't share.

You asked earlier about how many 'PF's' have been convicted; the lack of any response speaks volumes to me."

In response to the question you pose above, let's be certain about this, there is nodody who can tell you categorically what the extent of the Peregrine breeding population is likely to become in the future, there are to many unknown factors which will determine the equalibrium of that species and any other for that matter. I doubt you will get anyone including the most eminent ornithologists in the UK to give you a direct answer without restrictions! That said, please don't continue harping on the same ground over and over again, if you want to do something constructive on this thread, answer a few of the questions that have been put to you?

There are many on this forum who understand only too well what you are attempting to put across, especially to those who are less well informed on the Raptor persecution situation. We understand only too well the fact that you would love to make a case for a change in the Wildlife Protection Laws, in particular pertaining to certain Raptor species, to enable your RPRA to legitimise a cull of what they term troublesome birds of prey. You will never succeed in bringing as you say, the two sides together while ever you continue along the misguided idea that you have a right to persecute Raptors!

The question about how many PF's have been prosecuted for Raptor persecution has been answered several times, both by myself and others on this forum. The real question is, how many PF's have got away with it for the reasons already stated. The same applies to how many keepers or other Raptor persecutors have been prosecuted. When you weigh up the total prosecutions against known Raptor persecutions, the figure is ludicrously low.

nirofo.

 

[nirofo]

This is another myth put out by the pro-raptor lobby. When a Peregrine Falcon attacks pigeons during a race, it goes for the first ones it sees which are the leaders. In other words the fastest (best) birds are attacked first and either killed or scattered, while the slower ones following on behind get through.

So the only 'natural selection' possible as a result of predation by Peregrine Falcons is to ultimately reduce the pigeon's racing ability, not improve it!

What's this pro raptor lobby you're on about Anthony, can you tell me where it is being run and who's in charge of it. Af far as I'm aware the Schedule One Protected Raptors don't need a pro lobby, they're already covered by legislated wildlife protection laws!!

This rubbish about the Peregrine going for the leader of the RP pack is a total falacy, the Raptors will always go for the prey they can single out from the rest, there's nearly always a straggler that's slightly adrift from the others in the flock. Why do you think birds like the waders always fly in tight flocks and always turn together, they do this to present the least possible opportunity to birds of prey, limiting kills to birds that can't quite keep up with the rest, or are less agile. I don't know how many Peregrine stoops and kills you've observed Anthony, but it can't be many otherwise you'd know the birds prefer to go for a seperate prey item, be it RP or any other species. If you have observed Peregrines going for the leading RP's by preference on a regular basis, then I would think it worthy of a paper in "British Birds".

nirofo.

 

[Anthony Morton]

My observations of Peregrines taking out Pigeons are the complete opposite. In about 400 observed kills the victim has always been a straggler or a lone bird

Jane,

Many thanks for the earlier statistical information and references. However I'm intrigued to know how you can identify any of the pigeons you've seen killed by Peregrine Falcons as stragglers - whether they are flying on their own or even in groups.

For a start, not all the racing pigeons you see passing through will be taking part in the same race, so in simple terms there is no way you would be able to tell whether the pigeon killed by a falcon was (say) a straggler in Race A, an 'average' performer in Race B, or the clear leader in race C. Bear in mind also that pigeon races are held over distances varying from 75 - 600 miles or more, which are referred to as 'sprint', 'middle distance' and 'long distance' races.

Therefore a bird apparently burning up the sky could be just an average sprinter, while what looks rather slow by comparison could be the Paula Radcliffe of the racing pigeon world. Sprint races can be won by birds achieving an average velocity of 2,000 yards per minute or more, while long distance races are frequently won at velocities of barely 1,000 yards per minute. Bear in mind that these velocities are the average distance travelled for every minute of the time it takes from the bird being released along with all the others, until it is clocked in at its home loft.

In a nutshell, it is impossible to say with any degree of certainty whatsoever which category a particular falcon victim would fall into. All we can say with certainty is that it will not be coming home, regardless of its past performances!

 

[nirofo]

Clearly a new breed of Peregrine is evolving - one that hoardes scores of dead pigeons in cliff top refrigerators. That would explain Anthony's "take out the leader" observation too. No more of this "just take the easiest bird to catch" shinnanegins

Hi Jane

I've seen this sort of thing happening with Short-eared and Long-eared Owls, the birds will store up a good few Voles to feed to the young, so that when prey becomes scarce they've got something to fall back on. I think the Peregrines must have been observing this and adapting it for their own use. If they are using refrigerators to store the prey, does that mean they have their own wind driven turbine generator.

I wonder, if the Peregrines are concentrating on taking out the leaders of the RP pack, does that mean they are bringing in 10 RP leaders per day to the eyrie and if so, how many RP's are passing through the Peregrines territory in a day, in a week, in a month?

nirofo.

 

[abagguley]

In a nutshell, it is impossible to say with any degree of certainty whatsoever which category a particular falcon victim would fall into.

I believe you are absolutely right when you say this, Anthony.

Which begs the question of why you previously said this:

When a Peregrine Falcon attacks pigeons during a race, it goes for the first ones it sees which are the leaders.

Adrian

 

[CBB]

Jane,

Many thanks for the earlier statistical information and references. However I'm intrigued to know how you can identify any of the pigeons you've seen killed by Peregrine Falcons as stragglers - whether they are flying on their own or even in groups.

For a start, not all the racing pigeons you see passing through will be taking part in the same race, so in simple terms there is no way you would be able to tell whether the pigeon killed by a falcon was (say) a straggler in Race A, an 'average' performer in Race B, or the clear leader in race C. Bear in mind also that pigeon races are held over distances varying from 75 - 600 miles or more, which are referred to as 'sprint', 'middle distance' and 'long distance' races.

Therefore a bird apparently burning up the sky could be just an average sprinter, while what looks rather slow by comparison could be the Paula Radcliffe of the racing pigeon world. Sprint races can be won by birds achieving an average velocity of 2,000 yards per minute or more, while long distance races are frequently won at velocities of barely 1,000 yards per minute. Bear in mind that these velocities are the average distance travelled for every minute of the time it takes from the bird being released along with all the others, until it is clocked in at its home loft.

In a nutshell, it is impossible to say with any degree of certainty whatsoever which category a particular falcon victim would fall into. All we can say with certainty is that it will not be coming home, regardless of its past performances!

But it would be helping the peregrines survive and move their numbers up. Possibly to over the two thousand mark.

 

[Jane Turner]

However I'm intrigued to know how you can identify any of the pigeons you've seen killed by Peregrine Falcons as stragglers - whether they are flying on their own or even in groups.

In a nutshell, it is impossible to say with any degree of certainty whatsoever which category a particular falcon victim would fall into. All we can say with certainty is that it will not be coming home, regardless of its past performances!

To remind you of the specific comment of yours I was responding to

In other words the fastest (best) birds are attacked first and either killed or scattered, while the slower ones following on behind get through.

I say again, I have only seen Peregrines take Ps from off the back of passing flocks or single birds.

I suspect RPs vulnerability is more related to their lack of street savvy than their speed or lack of it. Natural selection weeding out the ones that have no clue how to evade a falcon.

 

[Andrew Rowlands]

Jane,
... However I'm intrigued to know how you can identify any of the pigeons you've seen killed by Peregrine Falcons as stragglers - whether they are flying on their own or even in groups. ... <SNIP WAFFLE> ...
In a nutshell, it is impossible to say with any degree of certainty whatsoever which category a particular falcon victim would fall into. All we can say with certainty is that it will not be coming home, regardless of its past performances!

Anthony,

If I or another observer were to see a racer sitting around, we'd call it a straggler.

If it's flying by purposefully, we'd call it a racer.

Not too difficult a concept, is it?

 

[London Birder]

Anthony, you're agenda is bull, anything to keep your silly hobby safe from those nasty falcons and hawks huh, get a grip man...

you've avoided perfectly reasonble questions time and time again, you've started this thread merely as a vehicle to provoke discussion hoping in some way to garner some kind of support under the premise of pretending to be curious about what the late CM meant by the 2,000 pair limit question, something which even the most knowledgeable Peregrine worker cannot answer with any degree of certainty, not happy yet? ... your concerns centre around pigeon racing and the predation of pigeons by our raptors, not any concerns for the fate of the UK feral population (which is under no threat whatsoever from raptors) ... how about coming clean and acknowledging what is obvious to almost every birder who's participated in this thread ... I thought you were a birder! ... really and truthfully you're trying to protect your train set from being stood upon by bullies which don't really exist.

these racing organisations are an utter disgrace calling for the destruction of what they deem nusiance raptors ... and again, all in the name of a pastime, something they deem obviously more important than the welfare and prosperity of of our birds of prey.

try finding a hobby that doesn't condone the killing of these wonderful birds whilst using lies and snide misinformation to hoodwink.

 

[CBB]

Anthony, you're agenda is bull, anything to keep your silly hobby safe from those nasty falcons and hawks huh, get a grip man...

you've avoided perfectly reasonble questions time and time again, you've started this thread merely as a vehicle to provoke discussion hoping in some way to garner some kind of support under the premise of pretending to be curious about what the late CM meant by the 2,000 pair limit question, something which even the most knowledgeable Peregrine worker cannot answer with any degree of certainty, not happy yet? ... your concerns centre around pigeon racing and the predation of pigeons by our raptors, not any concerns for the fate of the UK feral population (which is under no threat whatsoever from raptors) ... how about coming clean and acknowledging what is obvious to almost every birder who's participated in this thread ... I thought you were a birder! ... really and truthfully you're trying to protect your train set from being stood upon by bullies which don't really exist.

these racing organisations are an utter disgrace calling for the destruction of what they deem nusiance raptors ... and again, all in the name of a pastime, something they deem obviously more important than the welfare and prosperity of of our birds of prey.

try finding a hobby that doesn't condone the killing of these wonderful birds whilst using lies and snide misinformation to hoodwink.

Well edited LB. I think that says it all for me. Couldn't agree more. :clap:

 

[Jos Stratford]

I think there should be a law banning these racing pigeons - I mean I can't even hang out my frilly knickers without that neighbour's bloody pigeons flying over and crapping all over then. I mean, can't you imagine how soul-destroying it is to spent the whole day lovingly washing my whites to ensure them whiter than white, then coming out to find them more dappled than the bleedin' pigeon loft next door. And, this is on my own property, I mean where's my legal recourse to go round throttle the owner and serve up his pigeons to the local raptor appreciation society for their annual dinner?

 

[Anthony Morton]

I think the gulf is wide enough down to your fellow hobbyists judging by the inane nonsense on the various websites ... nonsense like up to 10 pigeons per day at an eyrie, something which I've asked you about but you seem not willing to address, despite the empirical evidence of those who've actively watched eyries ... if there's a gulf that's down to the fanciers, no birder I know is anti-pigeon racing

LB,

I'm flattered that you think I'm the font of all wisdom with regarding all matters relating to pigeon racing, but I'm not.

The simple answer, and the reason I haven't replied earlier, is that I had nothing whatsoever to do with the website you are referring to, or its content.

Why not ask me where Lord Lucan is currently living, or whether Shergar is really pulling a milk float in Hackney instead!

 

[Anthony Morton]

can you source that Anthony?

reason I ask because that's not always the case in my experience, they equally take the birds which stand out the most, i.e. pigeons with more white in the plumage than average ... why are you on about racing pigeons again, the Peregrine doesn't differentiate between racers or local ferals ...

LB,

I've only got a limited amount of time today, but I promised you a reply to this posting which I will keep - despite some of your more recent uncomplimentary comments. So to (hopefully!) avoid the Boo-Boys and the nit-pickers, let me state that what follows is not taken from any dusty peer-reviewed reference works but rather from comments overheard or snippets of articles/letters read in the Fancy press.

Local experiments have been carried out to determine whether the choice of BOP's predating racing pigeons was influenced by colour. Believing that dark coloured birds were less likely to be predated, one fancier kept two teams of equal numbers, one of all dark coloured pigeons and the other containing light coloured birds. However the local Peregrine Falcons took equal numbers from each team, so he concluded that in his case the colour of the prey had no bearing on predation.

Contrary to your comments, I have also seen it suggested that pied racing pigeons, i.e those with varying degrees of white plumage, are LESS likely to be predated, not more so. This is thought to be because the white colouring breaks up the outline of the pigeon thus making it less recognisable to the predator, not more so. I seem to remember hearing something similar about the white neck-ring and wing bars on the Woodpigeon being a form of nature's own camouflage in action.

BTW, please don't accuse me of introducing the topic of racing pigeons, as this is just the result of others reading more into my postings than is either written or intended. They also try to suggest that I'm not interested in wild birds - WRONG!, have a hidden agenda - WRONG! and am calling for the wholesale destruction of raptors - WRONG AGAIN! That's the problem you see - when those involved started off by making incorrect assumptions and are still continuing to do so, they lose sight of the fox and just end up chasing their own tails.

Tally ho!

 

[London Birder]

LB,

I'm flattered that you think I'm the font of all wisdom with regarding all matters relating to pigeon racing, but I'm not.

The simple answer, and the reason I haven't replied earlier, is that I had nothing whatsoever to do with the website you are referring to, or its content.

Why not ask me where Lord Lucan is currently living, or whether Shergar is really pulling a milk float in Hackney instead!

yeah ok Anthony, whatever ... you've had your answer to your original question as best as people can answer it ... as a birder and a PF have you never questioned the morals and motivations of your fellow PF's