It took a while to find the source of the plaintive cries. I was in a park, near a playground. The voices of young children are a good at masking the vocalizations of baby birds. Finally I spotted the nest hole.
Then momma flew in, was only there for a second. One voice was momentarily silenced, the one who got the grub.
Off she went and the crying carried on, within the tree and without. Raising children is exhausting.