Koels are members of the cuckoo family and they also lay their eggs in a different species' nest. The taxonomy of this species is unsettled, with some authorities claiming that the Australian birds are a separate species from the Eastern Koel. This bird is a juvenile and looks similar to the females, which have black crowns. The males are all black with a grey bill and red eye.
1: Blue Gum Walk, Hornsby, 20/12/2009.