Reproductive biology

Cooperative breeding is common in the family, and has been studied in several thornbills and scrubwrens. Mostly, though, acanthizids breed as pairs with some being assisted by a third or fourth bird. The breeding season is typically late winter to early summer and several attempts are made each season. Nests are domed, often with a clear hood above the entrance, and those of gerygones are pendant, attached to foliage. Although usually placed in trees or shrubs, crannies and hollows are also used and some species nest on the ground. The most common clutch is two eggs, though up to five eggs have been recorded. Egg color ranges from white in the rock-warbler, and white with sparse spotting in Acanthiza and Gery-gone, to cream or buff with heavier spotting in many genera to plain chocolate in redthroat and speckled warblers (Chthon-icola sagittatus). Eggs are laid at 48-hour intervals and are incubated by the female alone. Incubation periods and dependency of the fledglings are long. Both parents, and sometimes helpers, feed the young. Many nests are lost to predators, especially larger birds, and others are parasitized

A mountain thornbill (Acanthiza katherina) at its nest. (Photo by Hans and Judy Beste/Animals Animals. Reproduced by permission.)

by bronze-cuckoos (Chrysococcyx). Annual adult survival is 80% or more for some species; high for such small birds.

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