Something had to give. Yesterday morning, the five very mature nestlings were crowded on the nest. I checked on them a few hours later and there were only two birds on the nest. I glanced overhead and saw the missing three perched on one of the rafters.
Today, all five were outside, perched on the roof of the boathouse. They took regular flights in the company of the adults and seemed very adept on the wing.
Full credit goes to my neighbour who only complained about the droppings.