Eudynamys scolopaceus Linnaeus, 1758

The male of the nominate race is glossy bluish-black, with a pale green or 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.They are very vocal during the breeding season (March to August in South Asia), 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 between the racesThey show a pattern of moult that differs from those of other parasitic cuckoos. The outer primaries show a transilient (alternating) ascending moult (P9-7-5-10-8-6) while the inner primaries are moulted in stepwise descending order (1-2-3-4). The Asian Koel is a brood parasite, and lays its single egg in the nests of a variety of birds, including the Jungle Crow,[13] and House Crow. In Sri Lanka it was known to parasitize only the Jungle Crow until the 1880 and later shifted to the House Crow.[14] About 5% of Corvus splendens nests and 0.5% of Corvus macrorhynchos nests were found to be parasitized in a study in India.[15] In Southern Thailand and the Malay Peninsula, Koels have shifted host from crows to mynas (Acridotheres sp.) as the latter became more common in the late 1900s.[8] In South Asia they have sometimes been found to parasitize the Black Drongo[16], the European Magpie and possibly the Black-headed Oriole.[18][19] Males may distract the hosts so that the female gets a chance to lay an egg in the nest.[20] More often however, the female visits the nest of the host alone.[8] The Koel is not known to lay eggs in an empty host nest and a study in Pakistan found that the first Koel eggs were laid, on average, within one and half days of the laying of the host's first egg.[21] The chicks of the Koel hatched about 3 days ahead of the host chicks.[22] Koels usually lay only an egg or two in a single nest but as many as seven to eleven eggs have been reported from some host nests.[2[25]A fmale may remove a host egg before laying. Eggs hatch in 12 to 14 days. The young Koel does not always push out eggs or evict the host chicks, and initially calls like a crow. The young fledge in 20 to 28 days.[8] Unlike as in some other cuckoos, the young do not attempt to kill the host chicks, a trait that is shared with the Channel-billed Cuckoos which are also largely frugivorous as adults.[26] It has been suggested that Koels, like some other brood parasites do not evict the host chicks due presumably due to the higher cost of evicting nestmates. A small parasite may not be able to evict large host eggs or chicks from a deep Corvid nest without risking starvation and possibly accidental self-eviction. An alternate hypothesis that retaining host chicks might benefit the Koel chicks did not gain much support.[27] Adult female koels have been known to feed young koels in the nests of the hosts,[28][29] Adult males have however not been noted to feed fledglings.[8] a behaviour known in some other brood parasitic species as well.