What is in that sad and soulful bird-call that I hear everyday pulling at my heart and soul?

Why does this bird call out so soulfully and to whom?

Everyday when I slide open the glass veranda door I hear the sad soulful call of this bird.

It never comes in view but remains hidden within the branches camouflaged by leaves that have just sprouted on trees and plants.
What is the sorrow of this little bird?