Images 1 to 6 show a face-off between two Asian Koels in a rain tree close to my apartment. One of them had been calling loudly from this tree for many days in mid-May. Then on the morning of the 24th I heard two distinct calls while I was having breakfast on the terrace. Looking out, I could see two males sitting on the same branch of the tree. Since they are usually hidden in the canopy, and I had never as yet managed to get a photo of an Asian Koel, I ran for my camera, and started shooting.
The two birds seemed quite tolerant of each other at first with no obvious threatening behaviour to be seen (image 3). Then one of them started calling even louder, mouth agape showing bright red inside. Very suddenly, there was a flurry of feathers as this one attacked the other (image 5 -- very blurred, but that is sort of how it looked). For a while there ensued a stand off, almost hidden behind some leafy branches. The one that had been on the receiving end of the initial onslaught then spread his wings, fanned his tail, opened his beak (image 6) and flew at his attacker who instantly fled, pursued by the winner right through the foliage of the rain tree and out the other side.
Since when there has again only been the call of one bird every day -- I assume the victor of this brief battle -- firmly back in control of his territory (for some reason I am convinced it was the original resident that won the confrontation).