In spring season, we often hear the musical or sweet voice of koel. We think that this sweet voice is produced by female koel. However, this sweet and musical sound is produced by male koel. Both the male and the female koels do not resemble with each other. The color of male koel is black and it looks like a crow, whereas the female koel is of ash colored and it has white spots on its body. Sweet voice can not be produced by the female koel.
Spring season is considered as the mating season for the koels. In this season the sweet voice is produced by the male koel to attract the female koel. The male koel stops producing sound as soon as the mating is over. This is the main reason that we hear the sweet voice of koel only in spring season. Since the crows make their nests near the human colonies therefore the female koel lays her eggs in their nests. After laying the eggs, the female koel flies away to the dense forests as it likes to live on big trees full of leaves to hide it. Their eggs are hatched by the crow.