Ornithological Basis

Ornithological basis for the list

White-throated Robin Irania gutturalis © Aurélien Audevard

Version 9.2 January 2024

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. Schläpfer 2018 provides a useful retrospective of the history of taxonomic listing in world bird species lists, ending with the current situation. Taxonomic decisions above the level of species are best made in a global context; hence the ORL originally was 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 frequent IOC on-line updates (at www.worldbirdnames.org, v14.1 at time of writing) that have supplanted Gill & Wright (2006). The updates summarise well-referenced taxonomic, order, sequence and name changes, both accepted and proposed. We adopt these revisions with few exceptions and document our reasoning. We have reviewed the ORL having evaluated Howard & Moore 4th edn Vols 1 & 2 at length. Many conclusions and decisions in H&M4 require assessment by IOC, but their extent and complexity will take much more time had been anticipated, and so we will follow IOC’s graduated approach, given that IOC have their own priorities. That said, the differences are mostly of degree, and are not radical. Furthermore, H&M4 conclusions will need evaluating in light of relevant papers published after H&M4 cut-off dates. 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. One of the ORL Team, Mike Blair, is a member of the IOC World Bird List Advisors’ Panel.

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 now-extinct British Ornithologists’ Union’s Taxonomic Subcommittee, whereby taxa were 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 departed from Dickinson (2003) on relatively few occasions, mostly to incorporate peer-reviewed taxonomic changes, cited in the ORL ‘Notes’ column. In similar fashion, occasionally we have departed from the IOC World Bird List, but we have included their recommended English names in curly brackets {…}. Since early 2022, the main World Lists have been rationalising their taxonomic differences, a circumstance that requires compromises to be made by each. This process has added some splits, but has also requires some earlier splits to be re-lumped, sometimes because of new evidence and sometimes because the spilt accepted by one list may not yet have been examined by the other lists. Consequently, the ORL policy as outlined below has at times caused us to diverge slightly from a few recent IOC changes, on a pro tem basis, while outlining the IOC position.

For some taxa, however, the decision is not clear-cut, and here we faced several choices. Indeed, much recent research has indicated that many more taxa than previously thought are in this category; e.g. see Olsson et al. (2010) (as analysed by Bannikova 2010) on the large grey shrikes (In ORL Passerine Reference List). They highlight the possible danger of relying on a single molecular marker, e.g. 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 might not fully conform with the organismal phylogeny, any proposed taxonomy is uncertain”. However, several recent authoritative references (up to and including January 2024) have not diverged from our earlier interpretation.

To add to the difficulties, an increasing number of taxa have been shown to have two lines of ancestry, inferring secondary contact between two long-separated populations when barriers to interbreeding have not developed, eg Sternkopf et al 2010 (In ORL Non-passerine Reference List).

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 two authorities in particular: first, Stephen Jay Gould (1977) who emphasised “the fuzziness of all supposedly absolute taxonomic distinctions” and second, Kees 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’ that causes little problem unless a rigid approach is insisted upon. However, we will consider the application of an Integrative Taxonomy approach, but we are aware that several variants are being developed on that subject. Pro tem, we will evaluate the views of Sangster 2018 on this subject. We take note of the cautionary exposition on the lack of a general understanding what species are by Raposo et al 2020, from which a few short quotations will suffice:

“It is important to distinguish between nomenclatural stability (one of the principles of the ICZN Code) which concerns the application of names to already known taxa, and taxonomic stability, the misleading impression that the definition of existing taxa should already have reached a fixed point—which is stressed in the assertion ‘taxonomic stability is ignorance’.

“Such an understanding has been reinforced by several contemporary authors aware that, at least from their philosophical standpoints, any taxonomic category imposed by a human mental concept, such as class, family, genus, species, or subspecies, are merely epistemological entities. Something totally different could be said for taxa (including species). In a phylogenetic or evolutionary perspective, taxa are hypotheses of relationships among specimens. Taxa fluctuate between categories and between hypotheses of relationships, which makes our efforts to circumscribe them ephemeral by definition.”

“In this case, the answer to the query is again concealed in the question itself: there is no species, but [merely] intellectual units inhabiting the minds of their descriptors and their respective followers and paradigms.” (Our insert)

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:

  1. Full biological speciesie those taxa which are (to all intents and purposes) completely reproductively isolated – eg Sardinian Warbler Sylvia melanocephala and Rüppell’s Warbler S. ruppeli.
  2. Subspeciesie taxa which have separate geographic ranges, 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.
  3. Allospeciesie 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, which we identify by using square brackets […] between the genus and species names. Allospecies come in pairs or groups, the group being called a superspecies.
  4. Superspecies – a group of allospecies or semispecies. As for allospecies, 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.
  5. 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.
  6. 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] trochiloides 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.
  7. 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 yarrelli as a subspecies, or Motacilla [alba] yarrelli as an allospecies or semispecies.

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) over the coming decade.

The use of scientific names from the ORL

Square-bracketed scientific names

As explained above, 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 views 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.


van Deemter, K. 2010. Not exactly: in praise of vagueness. OUP. Oxford, UK.
Gould, SJ. 1977. Original essay in Natural History Magazine Inc. Research Triangle Park. Durham North Carolina, USA. (In: Gould, SJ. 1978. Ever Since Darwin: Reflections in Natural History. Burnett Books/André Deutsch. London, UK.)
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.
Raposo, MA, GM Kirwan, ACC Lourenço, G Sobral, FA Bockmann and R Stopiglia. 2020. On the notions of taxonomic ‘impediment’, ‘gap’, ‘inflation’ and ‘anarchy’, and their effects on the field of conservation, Systematics and Biodiversity. Systematics & Biodiversity. (pp16) doi: 10.1080/14772000.2020.1829157
Sangster, G. 2018. Integrative Taxonomy of Birds: The Nature and Delimitation of Species: Chapter. In: DT Tietze (Ed): Bird Species. Fascinating Life Sciences. doi.org/10.1007/978-3-319-91689-7_2
Schläpfer, K. 2018. How many bird species are there? (2018). http://www.natureier.ch/pdf/How_many_bird_species.pdf.