The Acanthizidae, also known as the Australasian warblers, are a family of passerine birds which include gerygones, thornbills, and scrubwrens. The Acanthizidae consists of small to medium passerine birds, with a total length varying between. They have short rounded wings, slender bills, long legs, and a short tail. Most species have olive, grey, or brown plumage, although some have patches of a brighter yellow. The weebill is the smallest species of acanthizid, and the smallest Australian passerine; the largest is the pilotbird.
Taxonomy and systematics
Following the Sibley-Ahlquist taxonomy they were previously regarded as subfamily Acanthizinae within the family Pardalotidae. However, more recent molecular genetic studies do not support this arrangement. The Dasyornithidae are variously seen either as subfamily Dasyornithinae within the family Acanthizidae or Pardalotidae or as own family.
Acanthizids are native to Australia, Indonesia, New Zealand, and the southwest Pacific. Most species are found in Australia and New Guinea, with Australia having thirty-five endemic species and New Guinea fifteen. A single species is found in Vanuatu, New Caledonia and the Solomon Islands, and three species occur in the New Zealand region, including endemic species in the Chatham Islands and Norfolk Island. In Asia two species are restricted to Indonesia and another is found in the Philippines and on mainland Asia. Most species are sedentary, with the exception of the gerygones. The family occupies a range of habitats from rainforests to arid deserts.
Behaviour and ecology
Most species are terrestrial, feeding primarily on insects, although also eating some seeds. In particular the whitefaces consume large numbers of seeds, and other species will take fruits. The secretions of sap-sucking insects are favoured by some species, as are the insects themselves. Some species are less terrestrial, such as the weebill, which forages in the treetops, or the rock-dwelling rockwarbler. Rainforest species lay one to two eggs in a clutch, and species in the deserts and Tasmania lay three to four. Acanthizids are unusual for passerines in their long incubation periods, which rival those of large songbirds like the Corvidae. Also, despite their long incubation period hatching is completely synchronous and within-brood mortality completely absent. Acanthizids are relatively long-lived, with many species living to over ten yearsof age in the wild and cooperative breeding is found in the weebill and with a lesser degree of development in all whitefaces and most species of Sericornis and Acanthiza.
