OSME Region List of birds
Ornithological basis for the list
White-throated Robin/Iranie à gorge blanche Irania gutturalis © Aurélien Audevarde
The compilation of a species list for any major region requires its authors to address questions of taxonomy, and the OSME Region List (ORL) is no exception. Taxonomic decisions above the level of species are best made in a global context; hence the ORL is based on Dickinson (2003) Howard & Moore 3rd edn for Taxonomic Order and Sequence and on Gill & Wright (2006) Birds of the World: Recommended English Names – the published list of the International Ornithological Congress [IOC] regional sub-committees. We review the regular updates, published at www.worldbirdnames.com, to Gill & Wright (2006). These include summarised taxonomic changes, both accepted and proposed, that are well-referenced. We generally adopt these revisions, but do so with the caveat that we will review them when Howard & Moore 4th edn is published. We believe our approach not only presents the most up-to-date and well-researched methods of world lists available to us but also is accessible to birders in general. The main focus to our taxonomic work for the ORL has therefore been around species-level taxonomy. We have adopted a framework similar to that adopted by the British Ornithologists’ Union’s Taxonomic Subcommittee, whereby taxa are classed either as species, allospecies or semispecies within a superspecies, or subspecies within a species (see below). For the vast majority of taxa, allocation of taxonomic rank was straightforward. For these taxa, binomial and trinomial nomenclature is used for species and subspecies respectively; we have indicated allospecies and semispecies by inclusion of the name of the superspecies to which they belong in square brackets between the genus and species name (see fuller explanation below). We have departed from Dickinson (2003) on relatively few occasions, mostly to incorporate peer-reviewed taxonomic changes, which we cite in the ‘Notes’ column. We have departed from Gill & Wright (2006) also on very few occasions, but have included the Gill & Wright (IOC) recommended English names (as amended by their updates) in curly brackets {…}.
For some taxa, however, the decision is not clear-cut, and here we faced a number of choices. Indeed, much recent research has indicated that many more taxa than previously thought are in this category; eg see Olsson et al (2010) (as analysed by Bannikova 2010) on the large grey shrikes. They highlight the possible danger of relying on a single molecular marker,eg mtDNA, in taxonomic revisions and phylogenetic inferences, stating, “Since the mitochondrial gene tree deviates substantially from the (non-cladistic) interpretation of relationships based on morphological and ecological characteristics, and there are indications that the gene tree not fully conform with the organismal phylogeny, any proposed taxonomy is uncertain”.
We could have decided to ‘force’ these taxa into one rank or another (by choosing a default rank to assign in such cases, by following the majority position of previous authors, by tossing a coin in each case, or by other equally arbitrary methods), but we felt that that was an unscientific approach. At the other extreme, we could have chosen to study each case in detail and come up with our own considered view based on the available evidence. This avoids unnecessary delays in publishing each version of the ORL. We have therefore deferred a number of decisions until such time as further information is available. In such cases, we feel that our pragmatic approach clearly identifies this treatment as interim, and that we might be able to make more definite decisions in future. However, it is clear that sometimes the evolutionary state of some taxa is such that they are essentially undefinable in terms of rank, but we are strongly of the opinion that they should continue to be presented separately because they represent coherent populations, often over a wide geographical area. In support of our approach, we would cite van Deemter (2010), who elegantly demonstrates the circumstances in which the use of conceptual vagueness provides better understanding than a fruitless search for a ‘one-size-fits-all’ precise definition, citing taxa relationships as the prime example; for most taxa, rank is a ‘convenient fiction’ (van Deemter 2010) that causes little problem.
Determination of the status of the taxa listed
Our approach in the ORL presents practical ways of presenting the status of the taxa listed. It is not a definitive taxonomy in any way, but seeks not only to identify where knowledge of any taxon is imperfect, but also to keep it from being overlooked. The status of each taxon was considered to fall into one of the following categories:
- Full biological species – ie those taxa which are (to all intents and purposes) completely reproductively isolated – eg Sardinian Warbler Sylvia melanocephala and Rüppell's Warbler S. rueppelli.
- Subspecies – ie taxa which have separate geographic ranges and look different from each other in some way (where we want to recognise this variation), but where all are undoubtedly just different forms of the same species – eg two subspecies of Common Buzzard Buteo buteo are buteo and vulpinus (Steppe Buzzard) where trinomial names are used without need for any brackets – eg Buteo buteo vulpinus.
- Allospecies – ie taxa that have separate geographic breeding ranges (often in the past being classed as subspecies of a single species). These are taxa where we have ‘good reasons’ to believe that we are dealing with taxa which, if they were sympatric (ie sharing part of their geographic ranges), would behave as full biological species – eg there are differences in appearance, vocalisations or behaviour (in any combination) and in habitat or genetics (or both), which differences, if taken together, are comparable to those between known full species. Because such taxa are allopatric, we are making informed judgments, but in treating two taxa as allospecies, we are making a confident statement that we believe the evidence is good enough to warrant this status. Allospecies come in pairs or groups, the group being called a superspecies.
- Superspecies – a group of allospecies or semispecies. We put the superspecies name in square brackets […] between the genus and species names – eg Asian Desert Warbler Sylvia [nana] nana and African Desert Warbler Sylvia [nana] deserti.
- Semispecies – these are like allospecies, but come into contact in a hybrid zone. An extensive hybrid zone, spread over a large geographic area, would be a strong indicator that we are dealing with subspecies. What marks out semispecies as different, and warranting treatment as "fully tickable", is that there is something within the hybridisation acting as an effective barrier in keeping the two taxa apart (eg hybrids are less fit). Like allospecies, semispecies come in pairs or groups, and the term superspecies again applies to the group . The same convention applies as for allospecies – square brackets [..] – eg Carrion Crow Corvus [corone] corone and Hooded Crow Corvus [corone] cornix. With semispecies, we are again making a confident statement that we believe we have enough evidence for that judgement.
- Ring species – a ring species is a species that consists of a series of neighbouring populations, where no population is reproductively isolated from its neighbours, except for the two ‘end’ populations in the series, which are sympatric and reproductively isolated, and thus appear to be separate species – the name derives from the geographical distribution of the populations, which usually forms a ring.. A well-known example is that of the Greenish Warbler Phylloscopus [trochiloides] viridanus where the five subspecies – viridanus*, ludlowi*, trochiloides, obscuratus and plumbeitarsus* (those asterisked are recorded from the OSME Region) form a series around the Himalayas from northwest to northeast – with the northwesternmost (viridanus) occurring sympatrically with the northeasternmost (plumbeitarsus) without interbreeding. The square brackets indicate that Greenish Warbler forms a superspecies with Green Warbler P.[t.] nitidus.
- "Don't know" – our shorthand description of the final category. This is where the taxa could be full species, allospecies/semispecies, subspecies, or exist in identifiable populations that are intermediate in evolutionary terms. Also, it may be that we haven’t formed an opinion, because the evidence is not available, contradictory, or we are unsure whether it has been shown to apply sufficiently comprehensively (We may not have had time to discuss which treatment is appropriate Here we use round brackets (…) for the "Don't knows". In effect we are saying that – eg we use round brackets for Pied Wagtail Motacilla (alba) yarrelli, because there are a number of possible approaches, each of which may be correct, but we don't yet know which one, and so the end result may be Motacilla alba as a full species, Motacilla alba yarrellii as a subspecies, or Motacilla [alba] yarrellii as an allospecies or semi species.
Improved understanding of the relationships between species causes inevitable changes to checklist sequences and will continue to do so , some genera moving to a different family, or families themselves being subsumed in others. All world checklists are subject to such revisions – these arise from morphology, vocalisation studies, molecular biochemistry and other disciplines. Popular understanding of the limitations of DNA research is often poor, partly because the results are not easy to interpret and concern probabilities. Morphological differences do not invariably coincide geographically with DNA ‘breaks’ that show good separation ‘distances’ between taxa, although so far this is rare. We seek corroboration from other disciplines where use of a single DNA technique offers radical conclusions. We would expect DNA barcode analysis (Kerr et al 2007) of Palearctic species will provide some unexpected conclusions (Kevin Kerr pers comm).
The use of scientific names from the ORL
Square-bracketed scientific names
As explained in the Ornithological Basis, we use square brackets […]
in the ORL between the
genus and species names in the scientific names of allospecies or semispecies, and in superspecies,
which are groups of such allospecies and semispecies. However, there is a general convention of
omitting the square-bracketed part of the scientific name to simplify them in general correspondence
and in papers that do not deal with taxonomic aspects. You can see this in the output of the most
respected ornithological organisations, such as the British Ornithologists’ Union (BOU), for example,
in the Fifth Report of the Taxonomic Sub-committee of the BOU Records Committee, where the split is
accepted of Dark-throated Thrush Turdus ruficollis into Black-throated Thrush T. atrogularis and
Red-throated Thrush T. ruficollis. In the ORL, we present this information in a slightly different
way, as semispecies: we add a Parent Taxon row, to show more clearly
the former treatment from which
the change derives, thus: Dark-throated Thrush Turdus ruficollis, and then the semispecies rows
thus: Black-throated Thrush Turdus [ruficollis] atrogularis and Red-throated Thrush Turdus
[ruficollis] ruficollis.
There is no expressed intention that users of the ORL should include the square-bracketed part
of a taxon’s scientific name except when discussing it with us
Round-bracketed scientific names
Our use of round brackets (…) between the genus and species names in scientific names in the ORL indicates that there is a sizeable element of uncertainty as to the taxonomic status of the form in question. We would suggest users of the ORL follow suit in correspondence and in scientific papers. We invite comment on our taxonomic decisions (or perhaps more important, on the non-decisions) to help us improve the ORL. In particular, we are keen to hear view on those taxa which are confined or largely confined to the OSME Region. Whilst a considerable amount of work has been done on the taxonomy of birds in the northern Palearctic, and much is ongoing, less attention has been focussed on taxonomic problems relevant to the OSME Region. We hope that the OSME Region List can provide a vehicle through which this can be addressed.
References
Bannikova, A. 2010. On the molecular phylogeny in the genus Lanius. Appendix 2 In: Panov, EN.True Shrikes - Laniidae of the World. Ecology, Behavior, Evolution. Pensoft. Moscow, Russia.van Deemter, K. 2010. Not exactly: in praise of vagueness. OUP. Oxford, UK.
Dickinson, EC. 2003. (Ed). The Howard and Moore complete checklist of the birds of the world. 3rd edn. Christopher Helm. London. UK.
Fregin, S, M Haase, U Olsson and P Alström. 2009. Multi-locus phylogeny of the family Acrocephalidae (Aves: Passeriformes) – The traditional taxonomy overthrown. Mol. Phyl. & Evol. 52: 866-878.
Gill, F, & M Wright. 2006. Birds of the World: Recommended English Names. Princeton University Press. Princeton New Jersey. USA/Christopher Helm. London. UK.
IOC. 2010. World Bird List – Updates: www.worldbirdnames.com. (Summary updates of proposed/accepted taxonomy and English name changes.
Kerr, KCR, MY Stoeckle, CJ Dove, LA Weigt, CM Francis and PDN Hebert. 2007. Comprehensive DNA barcode coverage of North American birds. Mol. Ecol. Notes. (OnlineEarlyArticles) 17 Jan 07. doi: 10.1111/j.1471-8286.2006.01670.
Olsson, U, P Alström, L Svensson, M Aliabadian and P Sundberg. 2010. The Lanius excubitor (Aves, Passeriformes) conundrum—Taxonomic dilemma when molecular and non-molecular data tell different stories. Mol. Phyl. & Evol. 55(2): 347-357.
Parkin, DT and AG Knox. 2010. The Status of Birds in Britain and Ireland. Helm, A&C Black. London, UK.
Sangster, G, JM Collinson, AG Knox, DT Parkin and L Svensson. 2010. Taxonomic recommendations for British birds: Sixth report. Ibis 152: 180-186.