Should we stop some natural colonisers? (1 Viewer)

[ColinD]

The recent debate about Eagle Owl breeding in Lancashire, and the alledged threat to British raptors, brought to mind something I've been thinking about for a while (I've deliberately moved it off the Eagle Owl debate).

I remember years ago reading an article in a magazine (might have been British Birds), which suggested that even if the Brown-headed Cowbird made its way over here naturally, it should not be allowed to breed in Britain. If I remember correctly, this was because the author considered that as a parasitic species, the damage it could do to our native bird populations could be huge. I think it was around the time that one had been seen in Britain.

Perhaps I've got the exact detail of the article wrong, but that doesn't really matter. In principle, how would people feel about stopping the natural colonisation of Britain by a species which could cause damage to our native birds, especially a non-European species such as Brown-headed Cowbird?

My opinion is, it's easy to be appalled at what would be inteferance by Man, but the fact is, virtually the whole of Britain is Man made, even the bits we consider to be our protected countryside. Almost nothing is untouched by our actions, even the remotest regions. We've put many of our species under severe pressure, and many are in decline thanks to us. Therefore, if it came to it, we should take action to protect them from a species which could push them over the edge, even if that species was a natural coloniser.

It would be interesting to see what would happen if a pair of Ruddy Ducks with North American rings bred in Britain. Would we let them spread?

 

[Amarillo]

I would say you need to look at each situation individually.

If damage is likely to be caused to our native birds then I think it is justified to intervene.

 

[Gentoo]

Normally, I'm for letting nature take its course but you bring up some good points here. At this point, nature has been so thoroughly disrupted that anythig that happens wouldn't have natural results anyway. Brown-Headed Cowbirds in Britain would have devastating effects on native birds. Even some populations of American birds, mostly on either coast, are suffering big declines because of the spread of cowbirds which was once a primarily great plains species.

As mentioned before, each case should be looked at individually. Should House Finches suddenly turn up in Britain, I don't think there's much to worry about there. Should cowbirds turn up, get rid of them fast!

 

[KnockerNorton]

It depends on what you can do about it. For example, if a common and ubiquitous species over the channel spreads here totally naturally, like collared dove, there's not a lot you can do about it. But if a species is spreading in small numbers only due to man-made measures like reintroductions and habitat creation (like the EO in Holland), then it becomes manageable in that it will be easy to remove or control them if we want to. Accidental colonisers, like Chinese Mitten Crabs and signal crayfish are not tolerated, so I can't see why we're going gooey-eyed over eagle owls.

In the USA, starlings may well be vagrants, but they're also introduced and cause serious damage. The problem is, they're too numerous and prolific to do anything about now. You have to decide whether they will be a problem (and the precautionary principle usually applies here, as by the time you know it will be too late, hence deliberate introductions of anything are illegal), and how you want to manage the countryside and the species you have.

My bee in the bonnet about EO is that I am concerned for ban owls and red kites specifically, and anything else they may target. I do not know if they will have an impact, maybe they wont. But evidence from the most similar environment (Holland) shows they prey on a lot of owls and raptors in that kind of landscape. And bearing in mind our kite population is small, and our barn owl population still tumbling, and the money and PR that's been spent on them, I think it's just plain bonkers to risk it for a species that there is not a single bit of evidence suggesting it was ever native (unlike, say, wolves or white-tailed eagles).

 

[Amarillo]

Accidental colonisers, like Chinese Mitten Crabs and signal crayfish are not tolerated, so I can't see why we're going gooey-eyed over eagle owls.

because these are species from different ecosystems half way round the world. I cannot think of a single example of a species introduced on a local level from one part of a continent to another, that has caused problems. Can you give me an example?

evidence from the most similar environment (Holland) shows they prey on a lot of owls and raptors in that kind of landscape. And bearing in mind our kite population is small, and our barn owl population still tumbling, and the money and PR that's been spent on them, I think it's just plain bonkers to risk it for a species that there is not a single bit of evidence suggesting it was ever native (unlike, say, wolves or white-tailed eagles).

The habitats eagle owls have appeared in in the UK have hardly been comparable to Holland. Much of northern and western Britain would appear to be far more suitable habitat for EO's than Holland.

If you've ever been to Holland you will know how much more numerous raptors are there than in Britain. They are simply taking the most abundant prey!

No-one is suggesting a deliberate introduction, but now they are here it seems crazy to interfere unless there is real evidence that they will cause problems.

 

[KnockerNorton]

No-one is suggesting a deliberate introduction, but now they are here it seems crazy to interfere unless there is real evidence that they will cause problems.

but this has been deliberate introductions, in all probability, in some cases. Or at least negligent, which in the law is the same thing.

The point is, unless we act now, it will be too late. You're advocating letting them get established and THEN see what damage they might do. But by then it will be very difficult to remove them. Right now, there may be less than 100 birds, and bearing in mind the evidence that they COULD be a problem for other rare or threatened native birds, and they are NOT native, then I think the onus is on us to take these escapees back into captivity, before they get like muntjac deer or signal crayfish or mink or grey squirrel.

Other species which have caused problems by transferring from a continent to an island include sycamore in the UK (dominates woods), possums in NZ, rat and mouse species to any island and, as mentioned on the other thread, mink and hedgehogs to UK or UK islands.

 

[johnraven]

I think you need to be very careful what you wish for in terms of interfering with nature. The hunting fraternity are actively looking for excuses to kill raptors as vermin, and letting them loose on anything is dangerous for all raptors.

The Eagle Owl pair in Yorkshire were shot. There is no chance of a raptor population becoming dangerously out of control in this country as at the first indication that it is okay to do so, the hunters would slaughter the lot, just as they have done numerous times in the past. They would probably finish off a bunch of other raptors while they're at it.

 

[Amarillo]

The point is, unless we act now, it will be too late. You're advocating letting them get established and THEN see what damage they might do.

As a top predator they are not going to multiply like grey squrrels or muntjac deer. The known pairs should be monitored, and the issue looked at by experts.

possums in NZ.

That is a very bad example. New Zealand and Australia are in no way comparable to Britain and mainland Europe. They are two entirely different ecosystems.

 

[Vultur]

I cannot think of a single example of a species introduced on a local level from one part of a continent to another, that has caused problems. Can you give me an example?

Yes - though it's not a bird. Falthead catfish from the Deep South introduced to the West. As large (they can routinely hit 20-40 lbs. in good waters, and the world record is somewhere over 120!), opportunistic carnivores, they have harmed the local populations of sunfish and other small fish. (However, like most things, whether this is significant gets into a political debate...)

Disclaimer: I am not from Europe so everything that follows may be totally off base

Do think this is relevant, however? No. I don't know eagle owls, but judging by the Great Horned Owl (a North American Bubo with very similar niche - top owl predator through most of the continent), they do eat smaller owls, but I'm not sure the predation is significant. (Owls, as predators, are much rarer and more alert than their mammal prey.)

I would love to see top-level predators, say Red Wolves or Black Bear, re-enter Texas. Predators are usually good for the ecosystem as a whole.

 

[Gentoo]

Yes - though it's not a bird. Falthead catfish from the Deep South introduced to the West. As large (they can routinely hit 20-40 lbs. in good waters, and the world record is somewhere over 120!), opportunistic carnivores, they have harmed the local populations of sunfish and other small fish. (However, like most things, whether this is significant gets into a political debate...)

Disclaimer: I am not from Europe so everything that follows may be totally off base

Do think this is relevant, however? No. I don't know eagle owls, but judging by the Great Horned Owl (a North American Bubo with very similar niche - top owl predator through most of the continent), they do eat smaller owls, but I'm not sure the predation is significant. (Owls, as predators, are much rarer and more alert than their mammal prey.)

I would love to see top-level predators, say Red Wolves or Black Bear, re-enter Texas. Predators are usually good for the ecosystem as a whole.

Another example, no bird related is the BullFrog Form the east to the west. It has done major damge in California especially.

 

[Gentoo]

Do think this is relevant, however? No. I don't know eagle owls, but judging by the Great Horned Owl (a North American Bubo with very similar niche - top owl predator through most of the continent), they do eat smaller owls, but I'm not sure the predation is significant. (Owls, as predators, are much rarer and more alert than their mammal prey.)

Acually the GHO has significant effects on other birds of prey. Peregrine Falcons have had [roblems when reintroduced and Barn Owls, Red-Shouldered Hawks and other species often drop in numbers when Great Horned Owls move in.

 

[citrinella]

I take the David Attenborough view : foreign species should not be introduced. Maybe we can't see negative effects, but you bet they will be there. I extend this to colonization. No, we should not turn a blind eye to it because there will be negative effects. Trouble is, it's impractical

because these are species from different ecosystems half way round the world. I cannot think of a single example of a species introduced on a local level from one part of a continent to another, that has caused problems. Can you give me an example?

Yes. Red-legged partridge have a severe negative effect on greys. There are two obvious effects :
1. direct competition for food and habitat;

2. red-legs dump odd eggs in other species nests. Fine if it is a pheasant, but if it is a grey the grey will desert. So breeding is also compromised.

There may be other effects, e.g. spread of disease, which are masked by the first two. There is another effect - shooters shoot the greys when they are really supposed to be shooting red-legs.

If you've ever been to Holland you will know how much more numerous raptors are there than in Britain. They are simply taking the most abundant prey!

Really ? When I visited Flevoland I thought it was an ecological desert. The Dutch had realized this and were belatedly planning to allow a few hundred hectares to wetland and scrub to form a nature reserve. What do Dutch census figures show ? I'd be surprised if they show more raptors.

No-one is suggesting a deliberate introduction, but now they are here it seems crazy to interfere unless there is real evidence that they will cause problems.

Except that we are useless at detecting problems. How often are we really clear about the reasons behind population changes, even if we study them quite hard ? If we ever did notice an effect, it would already be far too late for the victims.

Mike.

 

[Stevie babe]

In answer to the initial question my reply would be no.

Facts of the Eagle Owl have been given as
Habitat: Can be found from Europe across Russia to Pacific, South to Iran, Pakistan across to China and Korea. Eagle Owls occupy a variety of habitats, from coniferous forests to warm deserts. Rocky landscapes are often favored. Adequate food supply and nesting sites seem to be the most important prerequisites.

Diet: Will eat almost anything the moves - from beetles to deer fawns. The major part of their diet consists of mammals (Voles, rats, mice, foxes, hares etc...), but birds of all kinds are also taken, including crows, ducks, grouse, seabirds, and even other birds of prey (including other owls). Other prey taken includes snakes, lizards, frogs, fish, and crabs.

It seems to me, as was mentioned earlier in this thread that as our BOP situation in the UK is quite low, Eagle Owls will go for easier pickings and I would imagine that Squirrels could be top of the menu. OK that could mean Reds being taken but it could also mean that Greys get a natural predator as well so another introduction gets automatically checked. Why should they target Barn Owls anyway. Its not as if they have a label saying "hey I'm a barn Owl I'm ready to eat". Diet could also include Little Owls (for instance) another introduction. Anyway the above description suggests that the main part of the Eagle Owls diet is mammal based. Mice, Rats, Rabbits even Foxes (that should please farmers if fox hunting is only about removing a pest - which I don't agree with, and I have worked on a farm)

Taking the argument to eradicate introductions further, should artificially stocking of lakes & reservoirs be stopped (which in some cases can be detrimental for Ospreys, either as a stop over or for nesting - This is, I am told, is what has happenned at Bough Beech Reservoir, Kent.

There is hardly any limit now to spread of species. Another thread states what would you bet will be the next species to move into the UK. Almost a suggestion that we want new species to settle in the UK (and lets face it we have no problems letting the rest of the human world settle here) Global warming, whether natural or man made, will cause species to shift and for us the probability is for a northward movement. We would gain species but we would also lose some. That's a natural shift and, as far as I am concerned in this instance let nature take its course. Some new species could be here or about to spread to the UK because we have screwed up their environment elsewhere. What's the point of screwing it up for these species here as well.

I'm off my soap box now.

Steve

 

[Amarillo]

Yes. Red-legged partridge have a severe negative effect on greys. There are two obvious effects :
1. direct competition for food and habitat;

2. red-legs dump odd eggs in other species nests. Fine if it is a pheasant, but if it is a grey the grey will desert. So breeding is also compromised.

I'm not sure about that. I thought the decline of the grey partridge was more to do with farming practises. In any case, gamebirds are not a very good example as their populations and habitats are managed by humans to such a degree that its difficult to see how they would interact in a natural ecosystem.

Really ? When I visited Flevoland I thought it was an ecological desert. The Dutch had realized this and were belatedly planning to allow a few hundred hectares to wetland and scrub to form a nature reserve. What do Dutch census figures show ? I'd be surprised if they show more raptors.

Well in the parts of Holland I've been to I'm always amazed at the density of buzzards, there seems to be one soaring over every field. No doubt with the density of human population and intensity of agriculture there are areas like that however.

 

[KnockerNorton]

Yes - though it's not a bird. Falthead catfish from the Deep South introduced to the West. As large (they can routinely hit 20-40 lbs. in good waters, and the world record is somewhere over 120!), opportunistic carnivores, they have harmed the local populations of sunfish and other small fish. (However, like most things, whether this is significant gets into a political debate...)

Disclaimer: I am not from Europe so everything that follows may be totally off base

Do think this is relevant, however? No. I don't know eagle owls, but judging by the Great Horned Owl (a North American Bubo with very similar niche - top owl predator through most of the continent), they do eat smaller owls, but I'm not sure the predation is significant. (Owls, as predators, are much rarer and more alert than their mammal prey.)

I would love to see top-level predators, say Red Wolves or Black Bear, re-enter Texas. Predators are usually good for the ecosystem as a whole.

That also reminds me of Wells catfish in Britian, introduced from Europe. Or, indeed, Zander. Both seriously affect the other fish species where they are introduced in Britian.

Your comparison with Great Horned Owl isn't relevant as, as I've alreayd piointed out, Britian has a limited population of the other owls/raptors that are are not repopulated from the wider continent, unlike in Continental North America where there is much larger pool to populate from.

 

[KnockerNorton]

I'm not sure about that. I thought the decline of the grey partridge was more to do with farming practises. In any case, gamebirds are not a very good example as their populations and habitats are managed by humans to such a degree that its difficult to see how they would interact in a natural ecosystem.

I think I'm with Amarillo on this one.

 

[Gomphus]

We cannot wrap up our natural world in cotton wool and freeze it, it is a naturally evolving thing, things change, if a species expands naturally it is because it has found something in the enviroment that it likes... If it arrives naturally like Collared Dove, or say Cattle Egret which is expanding what right have we to say its in the wrong place, we are seeing evolution of our natural world in action, you could say we need to get over it, it happens, how do you think humans reached the UK?


I will be very suprised if Cowbirds get to a problem species in Europe in the near future, they have the small problem of the Atlantic ocean! There is as far as I know there is only one western palearctic record.... Ship assists are the obvious answer I suppose, like House Crow?
We talk about Ruddy Duck breeding from a wild pair, now I suppose it is a remote possibility but there are not many records of pure pairs of any North American wildfowl breeding in Northern Europe? Given the numbers of Ring-necked Duck etc I find that interesting.

 

[KnockerNorton]

We cannot wrap up our natural world in cotton wool and freeze it, it is a naturally evolving thing, things change, if a species expands naturally it is because it has found something in the enviroment that it likes... If it arrives naturally like Collared Dove, or say Cattle Egret which is expanding what right have we to say its in the wrong place, we are seeing evolution of our natural world in action, you could say we need to get over it, it happens, how do you think humans reached the UK?

Again though, using that logic you'd welcome any introduction, howveer it got here, and that includes mink, grey squirrel and crayfish. yes, things change, but our countryside is managed, and we are the ones trying to manage it for our own ends (either to conserve species we care about, or maintain biodiversity for the myriad of reasons proposed for it). So if you welcome grey squirrel, you'll have to say goodbye to reds, and lose that link with oru cultural history (from Beatrix Potter backwards), and if you want mink then you say goodbye to water voles (from Wind in the Willow backwards - 'Minky' never appeared in that story), and my argument is that if you welcome EO, or anything else, who knows what else you will have to say goodbye too?

After all, who'd have though we'd lose water vole due to mink to the extent that we have? We just don't know what the effect will be, but we do know that introductions of anything from anywhere usually DO have an effect. So it really is best to manage things for the status quo if we can.

 

[ColinD]

.....
After all, who'd have though we'd lose water vole due to mink to the extent that we have? We just don't know what the effect will be, but we do know that introductions of anything from anywhere usually DO have an effect. So it really is best to manage things for the status quo if we can.

I guess that the point I was trying to make when I started this debate, is that we don't really have a natural World as such in the UK. It's almost all Man made, and therefore any "new" species which colonise are taking advantage of habitat created by us, whilst many native species have been pushed out or to the brink by our actions or destruction of their habitat. In other words, we've given the newcomers an unfair advantage.

It would seem reasonable therefore to stop the spread of non-native species which could push our natives over the edge to extinction, especially if the newcomer is a known problem such as Brown-headed Cowbird (or dare I say it, an Eagle Owl).

If a pest species such as Dutch Elm beetle arrives in the UK, we try to stop it before it wipes out our trees. Should we not apply the same rules to birds?

 

[ColinD]

....
We talk about Ruddy Duck breeding from a wild pair, now I suppose it is a remote possibility but there are not many records of pure pairs of any North American wildfowl breeding in Northern Europe? Given the numbers of Ring-necked Duck etc I find that interesting.

A remote possibilty perhaps, yet released birds breed quite happily. Could they cross the Atlantic? Who knows, but Pied-billed Grebes can. It's all hypothetical, but would we allow Ruddy Ducks to spread in the UK if proven wild birds started breeding?