OSME Regional 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 believe this presents the most up-to-date and well-researched approach among the available world lists. It is also 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 retained the Gill & Wright (IOC) recommended English names in curly brackets.

For some taxa, however, the decision is not clear-cut, and here we faced a number of choices. 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 would have delayed the publication of the list considerably, however, and we felt the need for the ORL was too great to allow this to happen. We have therefore deferred a number of decisions until future editions of the ORL, because we feel that our pragmatic approach clearly identifies this treatment as temporary, and that in future versions of this list, we will be able to make more definite decisions on these taxa.

1. 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.
2. Subspecies – ie 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 the three subspecies of Dartford Warbler Sylvia undata are undata, toni and dartfordiensis, where trinomial names are used without need for any brackets – eg Sylvia undata dartfordiensis.
3. 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.
4. 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.
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). 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. "Don't know" – our shorthand description of the final category. This is where the taxa could be full species, allospecies/semispecies, or subspecies, and we haven’t formed an opinion, either because there isn't enough evidence available, or because the evidence is contradictory (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 has meant that checklist sequences inevitably have changed, 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 invite comment on our taxonomic decisions (or perhaps more important, on the non-decisions) to help us improve future versions of 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.