Proposal (189) to South American Classification Committee


Adopt guidelines for the assessment of introduced species


Summary: This proposal, if approved, would essentially adopt the BOU "Category C" model for the assessment of whether an introduced species should be included on the main list. The guidance would be used as a basis to assess whether any species had become "Introduced".


Proposed guidelines: The term "introduced species" would be interpreted as meaning the following:


"Species that, although introduced, now derive from the resulting self-sustaining populations:


Naturalized introduced species. Species that have occurred only as a result of introduction.

Naturalized established species. Species with established populations resulting from introduction by Man, but which also occur in an apparently natural state.

Naturalized re-established species. Species with populations successfully re-established by Man in areas of former occurrence.

Naturalized feral species. Domesticated species with populations established in the wild.

Vagrant naturalized species. Species from established naturalized populations abroad.

Former naturalized species. Species formerly placed in 1 whose naturalized population is either no longer self-sustaining or are considered extinct."



A recent example of how this works in practice is set out in Dudley (2005) for various bird species occurring in the British Isles.


These guidelines could be amended in the future by separate proposal to deal with any unusual cases. For example, the sixth category above was recently added by the BOU to cater for the case of a long-introduced Phasianidae species that appears now either to be in a decline towards extinction as an introduced species in Britain or which may already be extinct as such.


Discussion: At present, 11 bird species regarded as "introduced" are found on the main SACC list. At least one exotic bird species on the hypothetical list (Acridotheres cristatellus Crested Myna) and another proposed for inclusion on the hypothetical list (Streptopelia risoria Ringed Turtle-Dove, proposal #182) are species for which evidence of an established population may not be as strong as it could be.


Discussions connected with proposal #182 evidence a degree of uncertainty as to how the status of an introduced population is to be assessed by the SACC. This proposal is made with a view to clarifying this issue and allowing S. risoria to be assessed for the main list in due course.


The SACC, like the AOU, currently uses just one word - "introduced" - as a basis for assessments of exotics. Such an approach may be confusing because arguably a species could be said to be "introduced" as soon as it escapes from a cage. The status of species such as Budgerigars Melopsittacus undulatus, Chickens Gallus gallus, Black Swans Cygnus atratus and others that do not typically establish wild populations thus becomes a question. S. risoria is a case in point, with populations (in the sense of apparently more than just isolated escapees) existing in the wild, but the jury out on whether it is established long-term. An element of establishment or sustainability generally is required to be presented to most bird committees before an exotic is added to a national list and seems to be assumed by the AOU and the SACC. Any other approach would mean that committee time would be wasted assessing numerous escaped cage birds. However, a decision over whether a species should be added to the main list could be criticized as being opaque unless more detailed guidelines are adopted.


In South America, with a larger avifauna, introduced species have, rightly, been subject to relatively little attention. However, this question may become increasingly important in assessing national or regional avifaunas (e.g. introduced psittacids species from other areas). Further, detailed guidelines would help in assessing the situation of A. cristatellus, S. risoria, the 11 species currently on the full list (if challenged), and any future proposals of new exotics. As described further below, tough guidelines would also discourage proposals for escaped cage birds, meaning that the committee can focus on more important issues.


In the UK, the question of introduced species has been subject to much attention by the BOU for two main reasons. First, legal protection for bird species derives from BOU categories. Introduced populations are generally protected (subject to e.g. culling licenses), whereas escaped birds can be recaptured and put into cages or even shot, subject only to cruelty laws (see further Donegan, 2005). Secondly, with a much smaller avifauna, the addition or inclusion of a handful of "dodgy species" could mean one birder's year or life list beating another's. This has led to much scrutiny and discussion of the topic on the part of birders and raises the stakes somewhat for the relevant committee. These factors have together led to a detailed and considered approach being adopted. I am not suggesting that BOU Category C is a perfect model for the assessment of introduced species. However, it is a jolly good one. Although aspects of the wording could arguably be improved, I would suggest that rather than "reinventing the wheel", these guidelines could simply be adopted by SACC. The BOU guidelines are a conservative set of guidelines that to date have resulted in just ten bird species being added to "Category C" in the UK, compared to over 200 species recorded in an escaped condition that have not been (see BOU, 2005 for list of those not accepted: Categories "D" and "E"). These guidelines thus promote long-term stability.


For example, the case of S. risoria would turn from:


Q: "Is it introduced?" A: "Maybe, I do not know what that means."




Q: "Is it a domesticated species with a self-sustaining population established in the wild?" A: "The species has shown itself to be capable of establishing such populations in other parts of the world. Therefore, the burden of proof may be lower than for other species. However, we need to go back in a few years to see if the birds are still there. Then we will be able to assess the situation."


Voting: A "Yes" vote would adopt the guidelines set out above for the assessment of introduced species. A "No" vote would simply retain "Introduced" status without any guidance as to what the term means.



BOU. 2005. The British List.

DONEGAN T.M. (2004) The legal protection of birds in Britain - and the need for reform. Birding World 17 (4) (May 2004): 157 - 165. (I can provide a .pdf to any committee member if more information on the context of the BOU guidelines is desired.)

DUDLEY, S.P. (2005). Changes to Category C of the British List. Ibis 147 (4), 803-820. Available at:


Thomas Donegan, November 2005




Comments from Zimmer: "NO. This actually brings me back to my comments on Proposal #182. I would vote "YES" on adopting guidelines. I'm not sure on first pass that the proposed BOU guidelines are the ones we want to adopt. Something about the language in all of those categories left me with the impression of an overly nuanced legal document. Can't we get it more straightforward than that? My vote is to adopt guidelines, just not these specific ones."


Comments from Robbins: "NO. Yes, we need to provide more guidelines in our definition of the term "introduced", but I agree with Kevin's sentiments that what is presented is too atomized and we surely can do better with fewer and simpler definitions. Thus, I vote "no" until we have a better set of definitions. By the way, one of my last actions as chair of the ABA CLC was to establish a subcommittee that is going provide consistent guidelines for dealing with introduced species in the ABA area. We might want to consult what they come up with in refining our definition."


Comments from Stiles: "NO to Donegan's specific recommendation that we adopt the BOU system, but YES we could do with more specific criteria. There are really only two questions: is (or was) X species introduced? and is (or was) X species established? The essence of introduction is that direct human intervention (intentional or otherwise) was responsible for its being in South America: without transport by humans, it wouldn't be here. Establishment implies that it is surviving and reproducing without direct, overt human intervention like provision of nest boxes or food required by the species. Distinguishing between escapes and intentional introductions is often impossible: there are all shades of grey in between, such as the confiscated birds released at the airport by ignorant customs officials, those released from pet stores or mercados by misguided animal lovers... I see the need for only two main categories (with an intermediate "limbo" for species for which data are insufficient to allocate them to one of the principal categories. These are "Introduced, not established" and "Introduced, not established", with a category "Introduced, status unknown" for those species where establishment has not been established, as it were - that is, we don´t know. All else seems too much like hairsplitting and would likely cause more headaches than it cures."


Additional comments from Donegan: "In response to charges of 'atomization', there is only one test in the BOU formulation, namely:


'Species that, although introduced, now derive from the resulting self-sustaining populations'.


"The six examples then provided are intended to provide some clarification. E.g feral species, vagrants from sustaining populations and reintroductions are all acceptable. The key concept is therefore self-sustainability, which is I would argue the same as Gary's concept of "establishment".


"The Dudley article cited above explained this concept as follows: '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.'


"As stated in the proposal, although this may not be agreeable to all, I would counsel against reinventing the wheel!"


Comments from Jaramillo: "NO - For the same reasons others object, this seems too complicated. I clearly think we need guidelines though, don't get me wrong! What is the standard used by the North American AOU list? If that is something that appeals to all, well it would at least be a consistent set of criteria used in the Americas, and I find that attractive."


"With regards to self-sustaining, this is very, very difficult to get a handle on as it depends on how long you sample the population. Crested Mynas were self-sustaining for a long time in British Columbia and Washington, but in the end the population died out. So was it self-sustaining? Well it depends on the time scale you looked at! Even though from a biological point of view choosing a standard set of time that a population persists is not necessarily that meaningful, it is easy to score. I gather that 10 years has been a standard in North America, which may be a bit too short a time span.


"Perhaps this is not the place to note this, but populations of Barbary/Ringed Turtle Dove, at least in North America, have not been self-sustaining. Most have died out, or have been thought to have been maintained due to releases or further escapes."


Comments from Nores: "NO. Me parece que para el propósito de la lista SACC es un número exagerado de categorías. Pienso que el hecho de que una especie dada haya sido introducida intencionalmente por el hombre, escapada de cautiverio o es de origen feral, tiene en general poca importancia. Lo fundamental para incorporarla a la lista SACC sería que la especie tenga poblaciones silvestres establecidas, como es el caso del House Sparrow (Passer domesticus) y la Rock Dove (Columba livia) en muchos países de Sudamérica, y el European Starling (Sturnus vulgaris), el Greenfinch (Carduelis chloris) y la California Quail (Lophortyx californicus) en Argentina. El comentario adicional de Donegan "Species that, although introduced, now derive from the resulting self-sustaining populations" me parece muy apropiado."