Developments in several fields of study (including bio‐acoustics and the analysis of DNA) together with reappraisals of the nature of species have impacted significantly on avian taxonomy. The BOU's Taxonomic Subcommittee has developed guidelines for the application of species limits to sympatric, parapatric, allopatric and hybridizing taxa. These are published here to assist researchers understand the rationale behind the committee's taxonomic recommendations relating to the British List.

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These recommendations of the Taxonomic Sub-committee of the BOU Records Committee will take effect immediately for the purposes of the British List. A paper outlining the approach of the Sub-committee to species-level decisions has recently been published (Helbig et al . 2002. Guidelines for assigning species rank. Ibis 144 : 518-525). The position of Anseriformes and GalliformesA review has been undertaken of 26 phylogenetic studies of the basal clades of birds. This review indicates that the basal subdivisions of living birds are well resolved, and that each of the five hypotheses below is well supported and that these hypotheses are much better supported than any alternative hypothesis.The best supported alternative hypothesis, supported by four mtDNA sequence studies, suggests that Passeriformes is the sister-group to all other living birds. Jackknife analyses of mitochondrial DNA sequences of all orders of living birds have shown that this finding may be an artefactual result of longbranch attraction due to insufficient taxon sampling.The following hypotheses are accepted: • The most basal subdivision of living birds is that between Palaeognathae and Neognathae; • Ratitae and Tinamiformes are sister taxa; • Galloanserae and Neoaves are sister taxa; • Anseriformes and Galliformes are sister taxa; • Neoaves is monophyletic.Galloanserae will therefore be placed at the start of the British List. Within Galloanserae, Anseriformes will precede Galliformes. The sequence within the families remains unchanged for now. A paper on this proposal has been completed and will appear elsewhere. cauta , T. chrysostoma and T. melanophris ), and the sooty albatrosses ( Phoebetria , comprising P. fusca and P. palpebrata ). The same studies indicate that the sooty albatrosses are the sister-group of the mollymawks rather than the sister-group to all remaining albatrosses and that the genus Diomedea , as traditionally defined, is not monophyletic. We recommend the recognition of the genera Phoebastria and Thalassarche because this underscores the existence of four major groups of albatrosses and eliminates paraphyly of the traditional genus Diomedea . Black-browed Albatross Diomedea melanophrisBlack-browed Albatross becomes Thalassarche melanophris. A paper on the generic status of albatrosses has been completed and will appear elsewhere. Greater Flamingo Phoenicopterus ruberGreater Flamingo Phoenicopterus ruber roseus , Caribbean Flamingo P. r. ruber and Chilean Flamingo P. r. chilensis are well-marked taxa that show consistent *Corresponding author. Email: a.g.knox@abdn.ac.uk †This paper is an official document of the British Ornithologists' Union.

Within the strongly polytypic Red Crossbill L. curvirostra there are many reports of two or more ‘subspecies’ nesting sympatrically, without interbreeding. This 13‐year study examines one such case, in Scotland, where an endemic form is resident and another was thought to occur after irruptions from its main range in continental Europe. Both forms were present in the study area every year; sympatric breeding was proved in 9 years and probably occurred in the other four. There was no suggestion of interbreeding and the Scottish form should be treated as a separate species, L. scotica, the Scottish Crossbill. This is the only endemic species of bird in Britain and one of very few European endemics. The evolution of crossbills in Europe is discussed in the light of recent palynological evidence and the taxonomic status of the Parrot Crossbill L. pytyopsittacus is re‐examined.