A Hole is not a Chimney and can Never hold a Nest.

Rooks think this hole in the roof of the barn where some slates have slipped is a chimney. They perch by it, dropping twigs, as twigs would jam in a chimney and they could nest. Instead, here, they fall to the floor below: three barrow-loads I took out yesterday, a week's worth.
The barn is the oldest structure on the farm, pre-dating the Irish state by decades.
I'm assuming the rooks bully all the other birds to bring them twigs to drop into the unfillable hole. That's what's happening in the Irish state, anyway.