city pigeons are descended from rock pigeons which in nature breed on the ground on tall cliffs and stuff, they don’t really build proper nests. This is part of why they thrive in cities, since tall buildings are a perfect nesting opportunity.

I destroyed repeatedly a pigeon nest-in-building because of a nasty experience I had the previous year. These determined little birds lay a egg during the night next to A SINGLE BRANCH!
Latter they layed a second eggs unfortunately it has rolled over the edge of the balcony because of that.

Crazy birds…