GEOGRAPHIC VARIATION Two races are recognised. Differences in adult plumage colour have been described for birds breeding around the Black Sea, which Gavrilenko (1954) considered sufficiently distinct to treat as a separate race, which he named A. a. septima. These differences are slight and apparently depend on freshness of feathering (see Identification and Description) rather than geographical variation. Since Paddyfield Warbler is highly variable in appearance, there appear to be no consistent differences in either plumage coloration or measurements between A. a. septima in E Europe and W Asia and nominate agricola from C Asia.
A. a. agricola (Caspian and Aral Seas to W Mongolia and NW China, Tajikistan, E Iran and N Afghanistan) Described above.
A. a septima (Black Sea coast from Bulgaria and Romania to S Ukraine) Although averages slightly warmer than nominate agricola, we consider this race to be inseparable on plumage and structure from the nominate form (see Taxonomy and Systematics below). Vocalisations have not yet been studied in detail and playback may provide distinctions.
TAXONOMY AND SYSTEMATICS [...] Leisler et al. (1997) examined the cytochrome b DNA sequences from a range of Acrocephalus species and [...] investigated the genetic divergence between Paddyfield Warblers from Crimea and those of E Kazakhstan, and discovered a 4.5% sequence divergence between them. Such a significant difference is usually associated with taxa that have diverged to such an extent that they are treated as distinct species. Sangster (1997) supported their findings and suggested that A. a. septima may be a cryptic species. Until further studies which investigate vocalisations and behaviour of European and Asian birds are published, we have retained septima as a race of Paddyfield Warbler but recognise that this position may change in the future.