The grass warblers are small passerine birds belonging to the genus Locustella. Formerly placed in the paraphyletic "Old World warbler" assemblage, they are now considered the northernmost representatives of a largely Gondwanan family, the Locustellidae. These are rather drab brownish "warblers" usually associated with fairly open grassland, shrubs or marshes. Some are streaked, others plain, all are difficult to view. They are insectivorous. The most characteristic feature of this group is that the song of several species is a mechanical insect-like reeling which gives rise to the groups ...
Locustellidae is a newly recognized family of small insectivorous songbirds, formerly placed in the Old World warbler "wastebin" family. It contains the grass warblers, grassbirds, and the Bradypterus "bush warblers". These birds occur mainly in Eurasia, Africa, and the Australian region. The family name is sometimes given as Megaluridae, but Locustellidae has priority.
The species are smallish birds with tails that are usually long and pointed; the scientific name of the genus Megalurus in fact means "the large-tailed one" in plain English. They are less wren-like than the typical shrub-warblers Cettia but like these drab brownish or buffy all over. They tend to be larger and slimmer than Cettia though, and many have bold dark streaks on wings and/or underside. Most live in scrubland and frequently hunt food by clambering through thick tangled growth or pursuing it on the ground; they are perhaps the most terrestrial of the "warblers". Very unusual for Passeriformes, beginning evolution towards flightlessness is seen in some taxa.
Among the "warbler and babbler" superfamily Sylvioidea, the Locustellidae are closest to the Malagasy warblers, another newly recognized and hitherto unnamed family; the black-capped Donacobius atricapillus is an American relative derived from the same ancestral stock and not a wren was long believed.
A comprehensive molecular phylogenetic study of the grassbird family Locustellidae published in 2018 found that many of the genera, as then defined, were non-monophyletic. The resulting revision of the genus level taxonomy involved many changes including the resurrection of the genera Poodytes and Cincloramphus as well as the erection of a new genus Helopsaltes. The former genera Megalurulus and Buettikoferella become junior synonyms of Cincloramphus.
The family contains 68 species divided into 11 genera.
- Robsonius – ground warblers 3 species
- Helopsaltes – grasshopper warblers 6 species
- Bradypterus – megalurid bush warblers 12 species
- Megalurus – striated grassbird
- Elaphrornis – Sri Lanka bush warbler
- Malia – malia
- Poodytes – grassbirds 5 species including one extinct
- Cincloramphus 11 species
- Catriscus – fan-tailed grassbird
- Schoenicola – wide-tailed grassbirds 2 species
- Locustella – grass warblers 20 species