Newly published research has completely revised the genera of the bush-warbler family Cettidae, including a split in our own familiar species, Cetti's Warbler.
Cetti's Warbler is a frequent inhabitant of reedbeds in southern Britain, more often heard than seen, and is gradually spreading northwards having first colonised the country in 1973. It is generally agreed to have three subspecies, of which only one is found in Europe, and two, collectively known as 'Eastern Cetti's Warbler' in eastern Eurasia. Eastern Cetti's has been claimed once in Britain already at Combe Haven Marshes, East Sussex, on 19 October 2002, but has suspected on occasion elsewhere in the Western Palearctic.
The family Cettidae has been proposed within the warbler 'super family' Sylvoidea, to contain what appeared to be distinct lineages from analysis of a limited genetic dataset. A recent genetic analysis using a mitochondrial gene and three nuclear sequences not only splits Cetti's Warbler away from the rest of the bush-warblers of the genus Cettia as it currently stands, but also suggests that Eastern Cetti's is in fact a separate species; this news could provide an 'armchair tick' for birders who have seen the species in India, for example. All the forms of Cettis' Warbler itself will be retained in the genus, but most current Cettia species will be moved into two other genera.
Before the advent of genetic analyses, the relationships of some of the species now known to be closely related enough to include in Cettidae were unsuspected, and several have very short tails, bright plumage and head patterns not associated with typical 'bush warblers'. The study's results also suggest that the genus Cettia itself holds some species that have in fact evolved in parallel and are unrelated to each other, misleading previous taxonomists who based their conclusions on largely morphological criteria. The new study has found that the family sorts genetically into 13 clades holding seven genera, of which Cettia is now divided into three (Cettia, Horornis and Urosphena) leaving four others (Abroscopus, Tesia, Phyllergates and Tickellia); the latter two were formerly included in Horornis. The new generic arrangement far better represents the clumping of the wide-ranging morphologies of the family.
Though the family itself appears to fall into two major clades, these are not supported well enough at a basal level to actually split the family up and more data are needed. Certainly, the evolution of structure and plumage has been very complex in the Cettidae, obscuring relationships and leading to misclassification.
Alström, P, Höhna, S, Gelang, M, Ericson, P G P and Olsson, U. 2011. Non-monophyly and intricate morphological evolution within the avian family Cettidae revealed by multilocus analysis of a taxonomically densely sampled dataset. BMC Evolutionary Biology 11: 352
This paper (and others) can be accessed at Per Alström's website.