Extensive bush warbler reshuffle

Grasshopper Warbler is one of the species left unchanged in the new analysis, though other Locustellas may be split or lumped. Photo: Steve Young (www.birdsonfilm.com).
Grasshopper Warbler is one of the species left unchanged in the new analysis, though other Locustellas may be split or lumped. Photo: Steve Young (www.birdsonfilm.com).

A prospective comprehensive reshuffle of the bush warbler tribe Megalurinae has simplified its structure and indicated future lumps and splits in the clade, as well as being recommended for full family status, the Locustellidae.

This particular group of warblers, all formerly belonging to the Sylviidae or Old World Warblers – known as a non monophyletic group for some time now – is currently considered to be composed of seven genera: Bradypterus, Schoenicola, Megalurus, Cincloramphus, Dromaeocercus, Eremiornis and Locustella, which includes the familiar Grasshopper and Savi's Warblers.

However, a soon-to-be-published multi-gene study has confirmed that many of the species are not each others' closest relatives within each genera (as also suggested by several previous studies) and proposes a reshuffle into four genera, representing the four major clades in their study.

The first of the two major clades ('Clade A') consist of all current members of Locustella, the Asian species of Bradypterus and Japanese Swamp Warbler Megalurus pryeri, and this is divided into two further clades with some Locustella and all Asian Bradypterus in one, and other Locustella and M pryeri in the other. 'Clade B' is a dual African and Australasian radiation containing the African Bradypterus species, Brown Emu-Tail Dromaeocercus brunneus from Madagascar, Spinifexbird Eremiornis carteri, two Australian songlarks Cincloramphus and the three remaining Megalurus species. This again can be divided in two, with a less well-supported branch separating Fan-tailed Grassbird Schoenicola brevirostris and Striated Grassbird Megalurus palustris from the others, which are better supported in the team's statistical analysis.

The authors propose a restructuring of the family, as the molecular relationships contradict the current taxonomy as it stands. Changes suggested are that Asian and M pryeri are incorporated into Locustella; that Bradypterus is used for the African species only; and that Cincloramphus and Eremiornis are incorporated into Megalurus with the remaining three members of that genus.

Some taxa were not sampled in the analysis, and for that reason, Schoenicola stays as it is for the present, and the positions of Amphilais(from Madagascar), Megalurulus, Chaetornis and Elaphrornis – all from Asia – are yet to be investigated.

The authors also propose separating:

  • Two main subspecies of Gray's Grasshopper Warbler, Locustella faasciolata fasciolata and L f amnicola;
  • Two subspecific groups of Little Rush-warbler, Bradypterus baboecala tongensis/transvaalensis and B b centralis/elgonensis;
  • Two subspecific groups of Cameroon Scrub-Warbler, Bradypterus lopezi mariae/usambarae and B l ufipae;
  • Two subspecies of Striated Grassbird, M palustris toklao and M p forbesi.

Brown Bush-warbler Bradypterus luteoventris warrants further study, while the species pairs Pleske's Grasshopper-Warbler L pleskei and Middendorff's Grasshopper-Warbler L ochotensi, and Russet Bush-warbler B mandelli and Javan Bush-warbler B montis appear to have diverged very little, and may need to have their specific status revised.

Of the four genera recommended by the study, Megalurus remains non-monophyletic according to discrepancies in the current analysis and previously published studies, and in need of further work. However, it is apparent that a wholesale revision of the family is warranted and this study goes a long way towards achieving this.

Reference: Alström, P, Fregin, S, Norman, J A, Ericson, P G P, Christidis, L, and Olsson, U. 2011. Multilocus analysis of a taxonomically densely sampled dataset reveal extensive non-monophyly in the avian family Locustellidae. Molecular Phylogenetics and Evolution doi:10.1016/j.ympev.2010.12.012

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