Starling nest on black elder

This unusual growth of leaves on an otherwise leafless black elder bush occurs around this year's empty starling nest at the farm. The leaves remain green and don't fall. It must have something to do with birds' droppings acting like a topical fertilizer because I have never seen such a growth on this - or any - bush before. The starlings built the nest early this spring, unfortunately, on a black elder growing right next to the front door of the house. Nobody was showing up there that early in the year so they assumed it was a good spot, protected from the wind and shaded by the house, I guess. Unfortunately, gardening season began soon after their young hatched. I think the parents were afraid to return to the nest because soon a dead young starling was found at the house doorstep. I don't know if they managed to bring up any other of their young or if they only had that single one but they must have been hanging around the nest a lot in the early spring to fertilize this part of the bush so well.