The noise that sounded like tiles sliding off the roof (bugger, I thought, and turned over and tried to go back to sleep) wasn't tiles at all but a limb falling off one of the aspens in the field. Big tree, big limb- and the horses are gathered round it eating the leaves. So far as I can see the fall was unprovoked. There's no breeze (we should be so lucky) and when I did my tour of inspection there was no evidence of rot. The limb is propped against the trunk it broke away from and constitutes a hazard- it could fall further and squash a horse- so we need to call Matthew in.