A buzzing tree on Wedholme Flow

 

There was such a strange buzzing noise coming from half way up this tree that we stood awhile looking for some type of insect, though it seemed too early in the year for that to be possible. It turned out that it was a piece of bark being on our side being vibrated backwards and forwards. Our side was the side away from the wind, so my guess is that there was some kind of vortex shedding going on as the wind passed the tree - a bit round one side and then a bit round the other way. But is that possible if the tree is not vibrating as a wire would in the wind? Trees are flexible enough to move slightly and maybe that is enough coupled with the variability of the wind flow. Though thinking about it, it is probably the vortex shedding up and down that actually makes the wires move up and down, not the vibration causing the vortex shedding.