Yellow-footed green pigeon calling its flockmates

I have more than once noticed them gather in this tree and another nearby tree around sunset. After enjoying the last rays of the sun, it is time for them to depart for their roosting site in twos and threes. One day I found this lone bird looking quite lost without the others. In the end I guess it must have spotted them elsewhere and took off. The sun shining particularly brightly near the horizon that day highlighted the colors of the bird, especially against the sky.