The Asian koel (Eudynamys scolopaceus) is a member of the cuckoo order of birds, the Cuculiformes. It is found in the Indian Subcontinent, China, and Southeast Asia. It forms a superspecies with the closely related black-billed koels, and Pacific koels which are sometimes treated as subspecies. The Asian koel like many of its related cuckoo kin is a brood parasite that lays its eggs in the nests of crows and other hosts, who raise its young.
The Asian koel is a large and long-tailed cuckoo measuring 39–46 cm. The male of the nominate race is glossy bluish-black, with a pale greenish grey bill, the iris is crimson, and it has grey legs and feet. The female of the nominate race is brownish on the crown and has rufous streaks on the head. The back, rump and wing coverts are dark brown with white and buff spots. The underparts are whitish, but is heavily striped. The other subspecies differ in colouration and size. The upper plumage of young birds is more like that of the male and they have a black beak. They are very vocal during the breeding season (March to August in the Indian Subcontinent), with a range of different calls. The familiar song of the male is a repeated koo-Ooo. The female makes a shrill kik-kik-kik... call. Calls vary across populations.