The native grey warbler or riroriro (Gerygone igata) and the endemic Chatham Island warbler (Gerygone albofrontata) are New Zealand’s only members of the Australasian family Acanthizidae. They sing a delicate and complex trill, which Māori took as a seasonal reminder to plant their crops. The grey warbler weighs 6.5 grams; the Chatham Island species weighs 9 grams. Grey warblers have adapted well to human changes to the landscape, but Chatham Island warblers prefer undisturbed sites.
The female of both species builds an enclosed pear-shaped nest with a side entrance hole, usually hanging from a branch. She lays four white eggs with reddish speckles, each nearly one-quarter of her body weight, in seven days. The male defends the territory while the female incubates the eggs alone. Then he helps feed the chicks while she prepares to lay a second clutch.
A shining cuckoo may lay an egg into the warbler’s second clutch. The cuckoo chick hatches first and expels the warbler’s eggs or chicks. It is fed by the apparently unsuspecting warbler until it fledges.
Both species eat mainly invertebrates and some small fruits. They glean food from leaves, and sometimes the grey warbler hovers beside branches to catch prey.