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 Megaluridae.
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 group's scientific name.
Species breeding in temperate regions are strongly migratory.
The nine species are:
A fossil acrocoracoid from the Late Miocene (about 11 mya) of Rudabánya (NE Hungary) is quite similar to this bone in the present genus (Bernor et al. 2002). Given its rather early age (most Passerida genera are not known until the Pliocene), it is not too certain that it is correctly placed here, but it is highly likely to belong to the Megaluridae at the least. As the grass-warblers are the only known megalurid warblers from Europe, it is still quite likely that the bone piece belongs to a basal Locustella.