I have had different species of birds nesting in my garden during the many years that I have been living in my current house. But this is the first time that I encounter two sets of nesting at the same time.

For about a week or so, whenever I walked past my Nam Nam (Cynometra cauliflora) tree during certain times of the day, I would hear the loud flapping of wings as one or a pair of Pink-necked Green-pigeons (Treron vernans) flew off the branches in panic. I must have interrupted them checking the tree as a possible nesting site. With time, as the pigeons got used to me walking past, there would be no such panic flights, unless I stopped by the tree for a few seconds and looked among the branches.

Soon I noticed a crude platform of a nest build around some branches. A pigeon would sit quietly on the nest. Not sure whether male or female as I would not like to disturb it. Should I stopped nearby to peep at the bird, it would invariably fly off. Again with time the pigeons got used to me peeping.

There is a water tap by the tree where I draw water for my plants. Whenever I turned on the tap to fill my watering can, the noise from the water gushing into the can caused the bird in the nest to fly off. Again with time, even this noise failed to frighten it. Now I can even stand close by and stare at the pigeon without disturbing it. This is a sure sign that the pigeons were incubating the egg.
The last time a pair of Pink-necked Green-pigeons nested in my garden was in February 2005 (Wee, 2005). That experience was one of the reasons that led to my interest on bird behaviour (Wee, 2005). Birdwatchers then were only interested in increasing the ticks in their checklists. This led to the setting up of the BESG website… to encourage birdwatchers to take an interest in bird behaviour.

Around the same time that the pigeons were around the Nam Nam tree, I was alerted to another nesting a short distance away. It was a pair of Red-whiskered Bulbul (Pycnonotus jocosus) building their nest in my Belimbing (Averrhoa belimbi) tree. The nest was less obvious in this tree and the movements of the bulbuls were quieter. The bulbuls must also be incubating an egg as there were regular shift changing and there were always a bird in the nest at night.

The last time a pair of Red-whiskered Bulbul nested in my Belimbing tree was in April 2015. The nestling was probably taken by an Oriental Pied Hornbill just before it fledged. Now, more than three years later, another pair has made a nest in the tree again.
I am looking forward to the successful nesting of these two pairs of birds… and reporting their progress…
YC Wee
Singapore
27th February 2019
12th March 2019 update: There was a strong storm yesterday evening. I checked on the nest of the Pink-necked Green-pigeons after the storm and it was empty. The male that was brooding the chick before the storm was not there. This morning I looked into the nest. There was no chick or even a dead chick in the nest. As for the Red-whiskered Bulbul nesting, there had not been any sign of a bulbul in the nest for many days. So that nesting also failed. Two nestings, two failures.
Reference:
Wee, Y.C. (2005). Foraging a closer relationship with Pink-necked Green-pigeons. Nature Watch 13(3):16-22.