Scrub Warbler changes position

The desert-living Scrub Warbler has been show to be more closely related to Cetti's Warbler rather than the cisticolas, as previously thought.

A superficial, and probably convergent, similarity to the cisticolid warblers of Old World dry grasslands has led Scrub Warbler to be placed in systematic order with that group in the past. However, a study of its rictal bristles, claw and footpad structure in parallel with analysis of six genes (two mitochondrial and four nuclear) has shown it to be allied to the Cettidae, and possibly even quite closely related to the long-tailed tits of the family Aegithalidae.

The sandy arid desert and steppe species will be familiar to many birders who have travelled to North Africa, the Middle East and Central Asia, and has long been considered a relative of the prinias and cisticolas of the family Cisticolidae on the basis of structural and proportional characters.

The new study found that the rictal bristles around the base of the beak closely resembled Cettia bush warblers, as did the roundness of the tail and curvature of the claws. The fine detail of the toe pads differed from nearly all other passerines except cettid warblers and long-tailed tit relations. These morphological features were paralleled in the molecular analysis, which agreed with other recent analyses – using less genes but more taxa than the present study – that the traditional placing of Scrub Warbler needs revising.

The authors also speculate that the bird's two Western Palearctic subspecies groups (of the eight named taxa) – saharae and relatives in North Africa and nominate from Egypt eastwards – may be separate species, a thought that must have occurred to birders who have seen both forms. Wide mitochondrial DNA differences between saharae and inquieta indicate that comparison of the geographical separation and vocalisations of each major population may yet establish them as separate species.

Reference: Alström, P, Fjeldså, J, Fregin S and Olsson, U. 2011. Gross morphology betrays phylogeny: the Scrub Warbler Scotocerca inquieta is not a cisticolid. Ibis 153: 87-97.