The diet of Horsfield’s bronze-cuckoo consists mainly of insects and their larvae, particularly hairy caterpillars. However, this species also sometimes eats plant matter, such as berries. Horsfield’s bronze-cuckoo forages both in the trees and on the ground, and will also snatch insects from the air or take caterpillars hanging on sticky threads (2) (3).
Horsfield’s bronze-cuckoo may breed in almost any month in northern parts of its range (2) (3), but breeding usually takes place between July and February in the south (3). Like many other cuckoos, Horsfield’s bronze-cuckoo is a brood parasite which lays its eggs in the nests of other bird species. Horsfield’s bronze-cuckoo usually parasitises birds that build dome nests, particularly fairy-wrens (Maluridae species) and thornbills (Acanthiza species). However, it also sometimes uses the open cup nests of other species (2) (3) (6).
The female Horsfield’s bronze-cuckoo lays a single egg into each host nest (3) (8), generally laying in the early morning and visiting the nest for only a matter of seconds. At the same time, the female removes one of the host bird’s eggs, taking it away in her beak (2) (4) (8). The Horsfield’s bronze-cuckoo egg closely mimics those of this species’ main hosts (2) (4) (8), but if it is laid before those of the host bird, it may be built over or abandoned (3). Each female Horsfield’s bronze-cuckoo may lay up to 14 eggs each season, although around 6 eggs is more usual (9).
Horsfield’s bronze-cuckoo eggs hatch after about 12 days, and just a day or so after hatching the chick pushes the eggs and chicks of the host bird out of the nest. To complete its deception, the young cuckoo imitates the begging calls of the young of its host, and the host birds feed it as if it was their own chick (2) (3). The cuckoo chick leaves the nest at around 15 to 19 days old (2), and the adult birds continue to feed it for several more weeks (2) (3). Intriguingly, the superb fairy-wren (Malurus cyaneus) is able to detect and abandon Horsfield’s bronze-cuckoo chicks, as the adults call to their unhatched young and on hatching the chicks develop begging calls that match those of the adults. The cuckoo chick, however, is unable to learn these calls (2).
Adult Horsfield’s bronze-cuckoos are usually solitary (2) (6), and females occupy distinct breeding ranges that encompass the territories of a number of host birds (9). Pairs of Horsfield’s bronze-cuckoos have been found to be monogamous for as long as the female continues breeding (9).