Eagle Owls (1 Viewer)

RobinD said:

The most relevant point I can see is a reply by Andrew Kelly, the author of the isotope paper to an article on the RaptorPolitics web site at http://raptorpolitics.org.uk/?p=860
The gist of it is that the paper has been peer reviewed and that the 2H/1H signatures suggest the bird came from Scandinavia, althiugh it is not definative proof.

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Thanks RobinD this helps a little. It is good to see it will be published in BB, but will any of the peers reviewing it be competent in assessing isotopic analysis?

The comment by Kelly mentions only Deuteium/Protium ratios and that the bird appears to have "originated in an area with very low 2H/1H signatures". Not confident what this means but i assume Deuterium very rare. Very low detection will mean high error potential so i hope the work includes analysis of other isotopes such as 16O/18O.

what is the difference in 2H/1H ratios between Scandinavia and Northern Britain? Trawling the internet i only find very low resolution maps that suggest very little.

Presumably the Hydrogen is getting into birds via water, drunk or in food (do owls drink much?) and not inhaled water vapour (confirm anyone?). If largely via food then the isotope ratio is only suggesting the origin of the food, not the bird, thus an assumption is being made that all captive owls are fed on locally sourced food (perhaps reasonable but still an assumption). Even if they are, this bird could have been reared in captivity in Scandinavia then escaped and made its own way to Britain or been imported (illegally?).

Even if it is shown that this Eagle Owl got here under its own power from a wild population, so what? extrapolating such a result to the current GB population is too much.

I am aware that much of the concern here is in opposition to the proposed extirpation of the GB population. I too oppose culling of GB Eagle Owls but feel that appealing to such tentative "evidence" will not help. It is too easily dismissed. Far better to highlight the absence of evidence of harm to GB species in the hands of those who support a cull.

Ficedula said:

I too oppose culling of GB Eagle Owls but feel that appealing to such tentative "evidence" will not help. It is too easily dismissed. Far better to highlight the absence of evidence of harm to GB species in the hands of those who support a cull.

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Well put.

Sometimes conservation is not an exact science and common sense and logic can be more appropriate than "evidence"

Common sense and logic very strongly suggest that Eagle owls will have no negative impact - why don't they just get a team of experts together to make that judgment? Even if the anti's are correct and eagle owls never lived here in the past, would the fact that one individual crossed the sea accidentally mean that suddenly their effect would be different? When you think about it, the fact that one could cross the sea naturally is just as relevant as whether one actually did! Realistically the notion that no eagle owl has ever occurred in Britain naturally is extremely unlikely, so to consider it a totally alien species alongside parakeets and grey squirrels is a nonsense.

take a look at http://raptorpolitics.org.uk/ time is short before the FERA risk assessment is complete and they seem to be very one sided in their opinions, time is short if you wish to voice your concerns

Presumably if the species is put on Schedule 9 nobody will be able to fly their Eagle Owl outdoors in case it legs it and creates an offence?

John

Farnboro John said:

Presumably if the species is put on Schedule 9 nobody will be able to fly their Eagle Owl outdoors in case it legs it and creates an offence?

John

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There is some defra guidance about that and various other tricky cases under section 14, Sched 9, to the effect that flying raptors is OK if done "competently" and with the intention that the birds will come back .

Hi all

Whether this isotope analysis is accurate, I feel sure Eagle Owls do occur here as natural vagrants, even if only once in a blue moon - just because so many far less likely vagrants do turn up.

Yet this is not the same as saying the Eagle Owl is a native breeding British species. It puts it rather in the same category as Canada Geese - a sprinkling of vagrants, and a large population derived from introductions/escapes. I'd guess the number of vagrant Eagle Owls turning up here must be tiny - thus the lack of records from east coast watchpoints. Like vagrant Canada Geese, I imagine they'd never have been able to establish a breeding population.

I always look at wildlife issues from both a conservation and an animal welfare point of view. It seems to me unlikely these owls will ever be a mjaor problem for other species in Britain. But on the precautionary principle, I'd like to see these Eagle Owls removed now, while there are still few enough of them for it to be feasible to do it by non-lethal means (pricking eggs, capturing chicks and maybe adults for relocation to the continent).

cheers
James

James Blake said:

Yet this is not the same as saying the Eagle Owl is a native breeding British species. It puts it rather in the same category as Canada Geese - a sprinkling of vagrants, and a large population derived from introductions/escapes. I'd guess the number of vagrant Eagle Owls turning up here must be tiny - thus the lack of records from east coast watchpoints. Like vagrant Canada Geese, I imagine they'd never have been able to establish a breeding population.

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agree that the vagrants would be unlikely to start a population.

But given that EO's range across the whole continent in all kinds of habitats/climatic zones, don't you think its likely that they were once here - and would therefore still be here without the actions of humans?

Taking that into account along with the possibility of vagrants puts them surely in a different category to canada geese?

Amarillo said:

agree that the vagrants would be unlikely to start a population.

But given that EO's range across the whole continent in all kinds of habitats/climatic zones, don't you think its likely that they were once here - and would therefore still be here without the actions of humans?

Taking that into account along with the possibility of vagrants puts them surely in a different category to canada geese?

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Hi Amarillo

Agree that the analogy with Canada Geese is far from exact! For one thing, in Britain the Eagle Owls are interacting with a suite of species fairly similar to that found in their (undisputably) natural range on the continent. That can't be said of the Canadas.

Not sure if the Owls' wide range and adaptability makes it likely they were resident here anytime recently, given that the sea does seem to have been a genuine barrier to a lot of species which are well-established in northern France, Belgium and the Netherlands. But then I haven't kept up with the evidence for presence here since the BB article of a year or two ago.

cheers
James

Eagle Owl was present in Britain up until the last ice age (c.10,000 years BP) (Stewart 2007) but there is no evidence that supports natural occurrence since, and since the land bridge between Britain and the Continent disappeared (Melling et al 2008). If anyone who hasn’t seen the latter paper then please PM me your email address, or email me, and I will send you a PDF.

As to stable isotopes, changes in climatic conditions can be compared (e.g. comparing a movement between two different regions with significantly different rainfalls). Care needs to be taken when looking for differences between areas within what is considered to be the same climatic region (e.g NW Europe). If a bird moved from a 'wet' area to a 'dry' area, even within the same climatic region, this could result in an obvious indication in stable isotope analysis. So, for arguments sake, the Norfolk EO moved from a wet area and died in a dry (Brecks - a low rainfall area) area could show this. But how you would prove that the wet area was Scandinavia over say Northern England (were EOs have bred successfully in recent years ) would I expect be very difficult as I understand they would have similar isotope signatures.

By contrast, isotope analysis of Baikal Teal (Votier et al 2009) was relatively easy because of the vast differences in isotope signature between the low-rainfall far northeast Palearctic and the high rainfall west. It is also worth remembering that isotope signatures of feathers reflect the diet of the bird when it was growing its feathers. If a captive bird was fed on e.g. grain from eastern Europe, or on rats that had been fed on pellets made from grain from eastern Europe, then the bird would show a false signature suggesting east European origin. In short isotope analysis of feathers is not the silver bullet that most birders seem to think it is, but it can be useful in certain situations.

Refs
Melling, Tim., Dudley, Steve & Doherty, Paul. 2008. The Eagle Owl in Britain. British Birds 101: 478-490.

Stewart, John. 2007. The fossil and archaeological record of the Eagle Owl in Britain. British Birds 100: 481-486.Hi

Votier, Stephen, Bowen, Gabriel J. & Newton, Jason. 2009. Stable-hydrogen isotope analyses suggest natural vagrancy of Baikal Teal to Britain. British Birds 102: 697-699.

Steve Dudley said:

Eagle Owl was present in Britain up until the last ice age (c.10,000 years BP) (Stewart 2007) but there is no evidence that supports natural occurrence since, and since the land bridge between Britain and the Continent disappeared (Melling et al 2008). If anyone who hasn’t seen the latter paper then please PM me your email address, or email me, and I will send you a PDF.

As to stable isotopes, changes in climatic conditions can be compared (e.g. comparing a movement between two different regions with significantly different rainfalls). Care needs to be taken when looking for differences between areas within what is considered to be the same climatic region (e.g NW Europe). If a bird moved from a 'wet' area to a 'dry' area, even within the same climatic region, this could result in an obvious indication in stable isotope analysis. So, for arguments sake, the Norfolk EO moved from a wet area and died in a dry (Brecks - a low rainfall area) area could show this. But how you would prove that the wet area was Scandinavia over say Northern England (were EOs have bred successfully in recent years ) would I expect be very difficult as I understand they would have similar isotope signatures.

By contrast, isotope analysis of Baikal Teal (Votier et al 2009) was relatively easy because of the vast differences in isotope signature between the low-rainfall far northeast Palearctic and the high rainfall west. It is also worth remembering that isotope signatures of feathers reflect the diet of the bird when it was growing its feathers. If a captive bird was fed on e.g. grain from eastern Europe, or on rats that had been fed on pellets made from grain from eastern Europe, then the bird would show a false signature suggesting east European origin. In short isotope analysis of feathers is not the silver bullet that most birders seem to think it is, but it can be useful in certain situations.

Refs
Melling, Tim., Dudley, Steve & Doherty, Paul. 2008. The Eagle Owl in Britain. British Birds 101: 478-490.

Stewart, John. 2007. The fossil and archaeological record of the Eagle Owl in Britain. British Birds 100: 481-486.Hi

Votier, Stephen, Bowen, Gabriel J. & Newton, Jason. 2009. Stable-hydrogen isotope analyses suggest natural vagrancy of Baikal Teal to Britain. British Birds 102: 697-699.

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Excellent summary, and with citations! :clap::clap::clap:

I do think people should stop trying to convince themselves that this isotope analysis supports the case for the Eagle Owls. Far better to attack the lack of robust evidence of harm from EO's and the real motivation of those bringing the greatest pressure for a cull, ie the hunting lobby.

Ficedula said:

Excellent summary, and with citations! :clap::clap::clap:

I do think people should stop trying to convince themselves that this isotope analysis supports the case for the Eagle Owls. Far better to attack the lack of robust evidence of harm from EO's and the real motivation of those bringing the greatest pressure for a cull, ie the hunting lobby.

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I agree totally to quote someone else

The first thing that should concern anyone with a practical interest in the Eurasian eagle owl is the way the Risk Assessment document has been handled and publicised. It was only by sheer chance that the document was highlighted to members of the NWRPG last week.

Steph. A can of worms and/or some really good discussion!

Perhaps it is time to focus on the politics of Defra (or whatever they are called this week)! Why shoot eagle owls , but introduce WT eagles. That does not make sense!!!:cat::cat:

Well, Defra or not, Eagle Owl is protected under the current European law, escape or not.

Many Eagle Owls WERE recorded in Britain, from early historic accounts to recent sightings, but they are not on the list because natural vagrants and escaped birds were unrecognizable. Which is a very different situation from "not occuring in Britain". Now, with isotope analysis, there is a way.

Note also that historically, EO population in the whole NW Europe was hunted close to extinction. Which by itself is artifical man-made factor and prevented recent vagrants/colonization/recolonization to Britain. Now the population is visibly increasing, and ringed juveniles disperse for several 100. km. So the wild records are not unexpected.

I wish that effort put into tracing EO origin in Britain was put into disproving a rather persistent tale that they might be a threat to any British species. Although EO eat individual birds, they are not a threat to any bird or mammal on the population level in the Continental Europe.

Steve Dudley said:

If a captive bird was fed on e.g. grain from eastern Europe, or on rats that had been fed on pellets made from grain from eastern Europe, then the bird would show a false signature suggesting east European origin.

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I think the bird (or rats fed to it) would need also to drink water coming from the faraway area. Not likely at all. Correct me if I'm wrong.

jurek said:

I think the bird (or rats fed to it) would need also to drink water coming from the faraway area. Not likely at all. Correct me if I'm wrong.

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I stated my understanding of how this can work but I’m happy for anyone who works with stable isotopes to confirm this or not.


QUOTE=jurek;1709033] Many Eagle Owls WERE recorded in Britain, from early historic accounts to recent sightings, but they are not on the list because natural vagrants and escaped birds were unrecognizable. Which is a very different situation from "not occuring in Britain".[/QUOTE]

This is exactly what the Melling et al (2008) paper referred to in my earlier post covers. It reviews the historical literature and known claims of EO in Britain listing all known occurrences from 1678-1990. This paper also covers EO in captivity in Britain (using data from the Independent Bird Register), the likelihood of EOs escaping from captivity, and the likelihood of natural vagrancy to Britain based largely on ringing data from Scandinavia. I repeat my offer to send anyone a PDF of the paper. I just need your email address in a PM.

jurek said:

Note also that historically, EO population in the whole NW Europe was hunted close to extinction.

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What is your reference for this statement?

Eagle Owl has been persecuted across Europe, especially during the 19thC, but it has never been close to extinction (at least I have not seen any literature sources that supports this). Mikkola (1983) estimated the central and north European population as between 4571 - 6472 pairs (total based on 12 countries only, see Mikkola for these). This was about the time the first protection of EOs began and from which the population in some areas has since increased. So I take Mikkola's estimate as the low point at a time when persecution was still exercised and at the time (1983) EO was also a legal hunting quarry in Finland.

Persecution, whilst a major cause of decline, is by no means the only reason. Disturbance, habitat change/loss and toxic chemicals (in their prey) have all contributed to the decline and since many of these additional pressures are contemporary, they will have placed an increased (disproportionate?) amount of pressure on declining populations.

For those interested in EO diet and in particular other bird species predated by EOs, I suggest you read Mikkola for a fuller account. Mikkola states that depending on available mammal prey, birds can make up to 51% of an EO's diet and to quote Mikkola, included "crows, ducks, grouse, seabirds, and even other raptors and owls" (this from a study of 17,615 prey items from four countries). BWP (Cramp 1985) gives a list of bird species recorded as EO prey and these include "full-grown" Grey Heron, ad male Capercaillie and "full-grown" EOs, and also states that EOs "frequently takes raptors (Accipitriformes and Falconiformes) and other owl species, apparently more often than their abundance warrants." BWP also states that most bird prey is taken "full-grown". Many of these "full-grown" birds will be near-fledged young from nests - Mikkola refers to EOs predating a heronry 4.1 km from their own and a Common Buzzard nest 4.8 km away. EO hunting range is given as 10+ km.

My biggest problem with this debate is that people trot out all sorts of 'facts' with no evidence to support their claims. It would be helpful if others were able to provide references in order to substantiate their claims and for others to refer to.

Refs
Cramp, S (Ed). 1985. Handbook of the Birds of Europe the Middle East and North Africa (BWP). OUP, Oxford.

Melling, Tim., Dudley, Steve & Doherty, Paul. 2008. The Eagle Owl in Britain. British Birds 101: 478-490.

Mikkola, H. 1983. Owls of Europe. T & AD Poyser, Carlton.

jurek said:

I wish that effort put into tracing EO origin in Britain was put into disproving a rather persistent tale that they might be a threat to any British species. Although EO eat individual birds, they are not a threat to any bird or mammal on the population level in the Continental Europe.

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Sorry that's putting the cart before the horse! The first step is to consider how they got here. If they arrived naturally then there is no need to worry further because they are a natural part of our avifauna.

However the available evidence clearly indicates that the UK population is due to escapes, deliberate releases and their offspring (see the BB paper referred to by Steve Dudley).

PaulD said:

Sorry that's putting the cart before the horse! The first step is to consider how they got here. If they arrived naturally then there is no need to worry further because they are a natural part of our avifauna.

However the available evidence clearly indicates that the UK population is due to escapes, deliberate releases and their offspring (see the BB paper referred to by Steve Dudley).

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I cannot agree, natural does not = harmless and anyway GB semi-natural habitats are highly anthropogenic. The origin of the GB EO's will have no bearing on the damage they might or might not do, they are all EO's and will affect their prey and competitor species identically however they got here.

The first and most important question to be answered (the horse of your metaphor) is will EO's cause harm to GB fauna measurably greater than the harm caused by other historically established species (however they got here) that we are happy to tolerate. Those in favour of a cull must show that the substantially equivalent faunas on the near continent where EO's have recently arrived or increased have been effected detrimentally to a significant degree. As far as i know this has not been shown.

However this question is resolved the origin of the GB EO's is irrelevant, if EO's are going to lead to the extinction in GB of (eg) Golden Eagles then they must go. If they are going to affect Golden eagles no more than do WT Eagles then there is no justification for a cull. Their "naturalness" or otherwise should not impinge on this assessment.

I would like to suggest that this concern for the natural origins is a particular fetish of birdwatchers because of the "tickability" factor. The GB EO population is of mixed origin, some are known escapes, most are of unknown origin and it is a reasonable assumption that a few got here under their own steam. Even if ringing recovery proved the latter it would not suddenly convert all GB EO's into indigenous.

Hi Ficedula

I think you've expressed some important things really well.

As also became apparent on at least one other thread recently (about wild boar in Britain), I'd say that there are several common assumptions about wildlife which do not stand up to close scrutiny.

These assuptions are:
natural = good
unnatural = bad
created or influenced by humans = unnatural
independent of human influence = natural

IMO we have to manage the community of living things we are part of as best we can, aiming for a healthy and diverse ecosystem and following the best ethical standards we can. As far as I can see 'natural' can be a very useful working concept in conservation, but no more.

Jurek's suggestion that without human influence Eagle Owls on the continent would have been in more of a position to colonise Britain is an interesting one, but surely at best no more than an untestable hypothesis. But it does again show up how problematic the concept of 'natural' is.

I'd like to point out again that removing Eagle Owls doesn't necessarily have to mean killing them.

cheers
James

Ficedula

Well if you feel that birds colonising Britain naturally should be subject to a risk assessment to see if they will compete with species already present then I don’t think you will get much support.

Are Little Egrets competing with other species? How about Cetti’s Warblers – what impact are they having on some of the rarer insects in our southern wetlands? Sorry I can’t see any merit in having a committee to consider whether birds occurring here naturally might compete with other species. It sounds like a nightmare proposal in fact.

I would also challenge your assertion about Eagle Owls that “a few got here under their own steam”. What information is that based on? I think it is perfectly possible to look at the information from ringing recoveries etc and suggest that we haven’t seen a naturally occurring Eagle Owl for thousands of years.

Ficedula said its a reasonable assumption that a few have got here under their own steam. And its difficult to argue against that.

The probability of a naturally arriving bird being recognised as such is extremely slim. Not many EO's are ringed on the continent and an unringed bird would be assumed an escape once seen in the UK. It is completely unrealistic to assume that because we haven't proved that an EO has arrived here naturally, that it hasn't happened.