The eighteen recognised species of the genus Gerygone are an assemblage of small, drab-coloured birds found mostly in the Australo-Papuan region, with G. sulphurea found in the Malay Peninsula, Indonesia and the Philippines, and G. flavolateralis found in New Caledonia and Vanuatu. These are another group of birds that have tended to draw the short straw in the vernacular name stakes: G. igata, one of the most abundant of New Zealand's native birds, is usually identified by the uninspiring 'grey warbler'. Personally, I prefer the more onomatopoeiac Maori name for these lively little birds: 'riroriro' (it has been suggested in some circles that it could possibly be referred to as the 'grey gerygone'; this proposition shall be treated with the scorn that it deserves). The riroriro and its congeners feed on small insects that they mostly glean from leaves or small branches, generally in the middle to upper canopies (Ford 1985). A certain amount of their prey is caught in the air, while the riroriro and the brown warbler G. mouki of eastern Australia also forage in lower vegetation than other species. The riroriro is also the only Gerygone species known to forage on the ground (Keast & Recher 1997).
Somewhat unusually for a decently-speciose passerine genus, the circumscription of Gerygone has been fairly stable in recent years, and the genus has mostly been supported as monophyletic. The only exception of recent times has been the New Guinean G. cinerea, recently reclassified by Nyári & Joseph (2012) as a species of Acanthiza. In the early 1900s, some authors divided Gerygone species between smaller genera (for instance, the Australian ornithologist Gregory Mathews, who never met a genus he couldn't break down). One species so separated was the Chatham Island warbler G. albofrontata, which is something of an island giant compared to other Gerygone species, weighing about 12 g while other species are about 6 to 7 g (Keast & Recher 1997). Unfortunately, the Chatham Island warbler was not included in the phylogenetic analysis of Gerygone by Nyári & Joseph (2012), but it was not identified as significantly separate from other Gerygone species in the morphological analysis by Ford (1985).
Ford, J. 1985. Phylogeny of the acanthizid warbler genus Gerygone based on numerical analyses of morphological characters. Emu 86: 12-22.
Keast, A., & H. F. Recher. 1997. The adaptive zone of the genus Gerygone (Acanthizidae) as shown by morphology and feeding habits. Emu 97: 1-17.
Nyári, Á. S., & L. Joseph. 2012. Evolution in Australasian mangrove forests: multilocus phylogenetic analysis of the Gerygone warblers (Aves: Acanthizidae). PLoS One 7(2): e31840.