I watched an interesting altercation between male Koels. The dominant male on the left slowly crept up the roof while the second male retreated down the other side. They eventaully almost came face-to-face when the pursued bird then climbed up the other slope of the roof, again pursued by thte agressor. Eventually, the second bird flew to a tree behind the house and the agressor flew off in the other direction. This took place over at least 10 minutes, with a bit of flicking of feathers and raised tails etc. I didn't see or hear a female but no doubt there was one nearby.