Farewell to our house martins?

Last night our three young house martins (stone martins) were waiting on the stone slabs beneath their nest.

They didn't move at all. They'd done their test flights and were ready to leave. This morning the remains of their nest lay broken up on the floor. No going back! Their parents had seen to that.

Maybe they're among the birds sitting on the telephone wires above the house.

Update 13th August

They're back again, getting ready to sleep on the stone slabs.

Perhaps the nest collapsed under their weight?