Self-sustaining populations (1 Viewer)

[Andyt]

When does a group of birds become a self-sustaining population ?

While I assume that the sea eagles on the Scottish west coast are now considered a self-sustaining population, what about the re-introduced Red Kites ? When would the planned re-introduced sea eagles on the Scottish east coat become self-sustaining ? What about the Parakeets in the London area and smaller groups elsewhere ?

It assume that this will not solely depend on factors, such as numbers, but that other parameters, such as age of first reproduction, lifespan, brood size, etc. come into play.

Is there a definition of what constitutes a self-sustaining population ?

Andre

 

[Capercaillie71]

I would define a self-sustaining population as one where average annual productivity exceeds (or equals) annual mortality in the long term, with minimal direct human intervention. In addition the population would have to be sufficiently large and geographically spread to avoid the risk that a one-off natural event (weather, forest fires etc.) could result in the extinction of the population.

The parameters that you mention will vary between species and mean that what constitutes a self-sustaining population will differ between species.

I would guess that red kites in southern England are now self-sustaining, but those in northern Scotland are probably not yet.

 

[Tero]

It will be difficult to define a time frame that defines self sustaining. A dozen birds of a rare species may be all that there is, and they may hang in there for decades.

 

[njlarsen]

Lots of natural populations are not really safe from that one-off natural event: just to take one example, extinction of St. Kits/St. Christopher Bullfinch, viped out by a hurricane after the population had been limited to the highest part of the island by human encroachment on the remaining island for plantations.

For that reason, I would not include that in what defines a selfsustaining population. The ABA Checklist group seem to have established rules that they go by, but does anyone know the wording of those rules?

thanks
Niels

 

[johnraven]

I have attached an excerpt from a publication (Ibis Volume 147 Issue 4
Page 803 - October 2005) that has a useful discussion about the
definition of a self-sustaining population:



DUDLEY, S.P. (2005). Changes to Category C of the British List. Ibis 147
(4), 803-820. Available at:
http://www.blackwell-synergy.com/doi/full/10.1111/j.1474-919X.2005.00470
.x



=======================================

Determining a self-sustaining population



When considering individual, often isolated, populations, it needs to be
determined whether any population is self-sustaining. Such a definition
should apply equally to populations both of naturally occurring breeding
populations and to naturalized non-native or established feral
populations. An essential feature of sustainability is the likelihood
that succeeding generations will persist. This matters for both
short-lived and long-lived species. A population is deemed to be
self-sustaining if it is considered probable that succeeding generations
will persist without human interference. However, measuring
sustainability is not always easy. Populations of long-lived species
might survive for many years without breeding - and therefore without
problems such as habitat change (affecting nest-site, roost site and
feeding availability, fledging success and predator avoidance) being
detected - or without breeding very successfully, before eventually
becoming established. Alternatively, individual birds might continue to
live long after a population ceased to be self-sustaining. Conversely,
populations of short-lived species may persist in the short term through
many breeding cycles until environmental change occurs, and the
population rapidly declines to extinction.

The overall size of a self-sustaining population may only be small, but
the establishment, over time, results in a stable population which a
natural event (e.g. diverse weather affecting breeding or survival) is
unlikely to reduce to a less than self-sustainable level, and which
would require direct intervention by Man (intentionally or accidentally)
to reduce the population to such a level that it would be deemed no
longer to be self-sustainable. A self-sustaining population is therefore
defined as one that survives at, or increases beyond, what is assessed
to be a viable stable level in a natural state in the wild in Britain.

For the purposes of the British List, species are admitted to Categories
C1-C4 if their populations are deemed to be self-sustaining. When a
naturalized population declines to a level that is deemed to be no
longer self-sustaining, the species will be placed in Category C6 even
if some individuals persist in the wild, e.g. Lady Amherst's Pheasant.

This paper covers all species placed on Category C before
recategorization in 1996 (Holmes et al. 1998) as well as some species
currently on Categories A, B, C, D and/or E where categorization issues
have been identified. Some of the conclusions differ from those
previously published by the BOU (e.g. in Vinicombe et al. 1993) because
numbers of some populations have increased or, using the definition of
self-sustaining above, a species is now deemed to be self-sustaining.

=======================================

 

[Steve Dudley]

John, you just beat me to my own article! Nice one.

Andre, the article John has cited above is the criteria the BOU (I am their Senior Administrator) uses in relation to the British List. So, re. the re-established Red Kites, yes, they qualify for Category C of the British List as most (if not all) of the re-established populations are self-sustaining (just as White-tailed Eagle is as you stated, but unlike Osprey in Rutland which at present is not deemed to be).

The article also provides details of all Cat C species on the British List and their current categorisation.

Steve
watching British Dragonflies - see it at Birdfiar 2007 - www.wildlifebooks.com

 

[Andyt]

John & Steve,

Thanks for the article, which is very helpful. Two sentences, however, stick out:

'...measuring
sustainability is not always easy'

'For the purposes of the British List, species are admitted to Categories
C1-C4 if their populations are deemed to be self-sustaining.'

Note the word 'deemed' in the last sentence. It confirms my suspicion that the issue is not at all a straightforward one.

How does the BOU deem a population to be self-sustaining ? Am I right that it is based on long-term monitoring data but still a professional judgement at the end of the day, given the various parameters involved, the values of which may not all be available or known ?

If I interpret you right a Red Kite from a non-self-sustaining population is still part of the metapopulation on category C, as most of the other populations are self-sustaining and therefore acceptable as a 'British List' bird.

Likewise although the Rutland Water Osprey itself is not part of a self-sustaining population, it would be considered as part of a self-sustaining metapopulation and therefore part of the species on cat C, right ?

What about Mandarin Ducks (and similar species) that escape regularly throughout Britain. The Norfolk and other populations are self-sustaining I believe, yet a single bird away from these populations is not considered as being included in the British List and is instead considered belonging to cat E, as it cannot be unequivocally established whether it has originated from that population or not. Is that right ? If so, are we not using different criteria here ?

I am keen to hear your views on this.

 

[Steve Dudley]

Hi Andy

You are correct, it is far from straightforward, and our committee of 10 look at the monitoring data and take considered view of a species.

The BOU is only concerned with the national picture. We ourselves do not undertake monitoring. We simply review available evidence. If there is not enough evidence, then no decision is made.

Once a species is added to Category C we do not look at other populations. That is down ot the local recorders (usually bird clubs) to determine if their lcoal population falls withn self-sustaining and can be classed as Cat C. On a national level though, any individual bird from a Cat C species is effectively classed as Cat C. For instance, if it came to a court of law over say a shooting of a bird, the fact the species is on Cat C would mean it has more protection than a species not recognised on the British List, e.g. Ring-necked Parakeet is on Cat C and termed a British bird, whereas Monk Parakeet is not as it has not (yet!) satisfied self-sustainability criteria. But getting into legislative processes is even more of a minefield!

The main thing is that the British List is concerned solely with species, not individual birds. The British List simply lists those species that satisfy the criteria for each of the categorries based on available data. As a list it does not determine between individual birds.

Cheers, Steve

 

[Andyt]

Hi Steve,

Thanks for the additional information. I was aware that the ist deals with species and not individual birds; my wording was obviously not accurate enough to get this across. Sorry !

The 2005 paper on Changes to Category C of the British List goes into great detail in listing what populations are considered self-sustaining and which are not and is a great help. The problem is that populations change all the time and as far as I am aware local reports rarely give details about what is considered as a self-sustaining population at a local level.

Where I am still unclear is this: you mention that any individual bird from a Cat C species is effectively classed as Cat C. Clearly a Mandarin Duck from, say, Scotland, (or for that matter a Ring-necked Parakeet away from the London area) is not part of a self-sustaining population and can therefore not be considered for all intents and purposes as 'belonging' to a species on category C but is clearly an escape. Such birds should therefore not be countable on one's list but from what you say it would appear that such birds are still legally protected and treated in the same manner as birds from a self-sustaining population.

IN OTHER WORDS birds that are clearly escapes are legally protected as long as there is a self-sustaining population from that species somewhere in the UK ? If not, the Rutland Osprey could legally be shot.

I am keen to hear your views again.

Many thanks,

Andre

 

[Steve Dudley]

In the 2005 paper we included the details of the individual populations as this was the first time we were listing some species on Category C, so we thought it helpful that we reviewed all the documented populations and which of these satisfied Cat C criteria. We will do this for any new species being added to Cat C, but will not get involved in reviewing any other population of a species already on Cat C.

Re legal matters, since I, nor the BOU, are legislators, I can't comment in detail on how the law applies to individual birds rather than species. You would have to contact JNCC on that one.

Yes, a species on the British List is afforded protection, but what difference this makes to individuals considered NOT to be from one of the self-sustaining populations, I don't know. There may be some test cases which JNCC might be able to point to on this.

Even some species not on the British List are afforded protection under European Law if they are a native European species. So, a Bonelli's Eagle flying in off the sea in Kent is protected under EU law although it has never been accepted on to the British List.

Anyway, as I stated, if you want answers to legal questions then these should be sent to those who can provide a definitive answer.

 

[njlarsen]

It is a little strange to read the last post. In Denmark, a species is protected unless it is specifically included on a list of species that can be hunted. You make it sound as if the situation is reversed in the UK?

Niels

 

[Strandman]

It is a little strange to read the last post. In Denmark, a species is protected unless it is specifically included on a list of species that can be hunted. You make it sound as if the situation is reversed in the UK?

Niels

It's the same here- "wild birds" under EU law are protected here under Widlife and Countryside Act, independently of BOU listing decisions. So listing and protection may overlap, but they are separate issues.

 

[Andyt]

Steve,

Thanks for the additional information; much appreciated.

Can anybody elaborate on the legal issues raised ?

Andre

 

[Strandman]

Steve,

Thanks for the additional information; much appreciated.

Can anybody elaborate on the legal issues raised ?

Andre

If I have your question right, it is whether an obviously escaped individual which is remote from the locally self-sustaining population has the same protection as the individuals which form that local population.

The answer is that the protection system works at species level- but with a narrow exception. It is a defence under the WCA if you can show that the individual bird has been bred in captivity (that's bred in captivity- not just escaped from captivity). Have a look at the Eagle Owl threads if you can face it- the issue got an airing there.

So an obviously escaped captive-bred individual of a protected species may not be protected under WCA. But that doesn't mean that it is safe or wise to take a potshot at an escape- there are other private property, firearms and animal cruelty issues that may arise.

 

[Andyt]

ED,

Why is a distinction made between birds bred in captivity and birds escaped from captivity ?

Andre

 

[Strandman]

ED,

Why is a distinction made between birds bred in captivity and birds escaped from captivity ?

Andre

Good question- I've never had to look into it, but I think it may be because it provides a black- and-white test and ensures the exception from protection (section 1(6) WACA) only applies in a very narrow situation.

If the exception applied instead to any "escapes" from captivity, including birds originally taken into captivity from the wild, that might open up the exception a bit more. You would have to define the line between escapes and various kinds of release.