I haven't experienced this with pigeons on a Wisteria, but the greengage near the pond looks exactly as you have described, long stems with just the tufts on the end which they can't reach. Not much you can do about it, we open the window and shout 'bang' which is effective for that moment, but not much more! The Cherry tree further up the garden has been killed, with only one small twiggy branch left alive this year - due to pigeons stripping new shoots, the poor tree couldn't compete. It will have to go after the Clematis, which grows through it, has finished flowering. It's really irritating if you have hoards of pigeons, even the Ivy here has the new shoots stripped and bare branches.

This happened every year to a mature wisteria in the courtyard where I worked. The whole area was pigeon paradise. They never stripped it though and there were still many many flowers even though there seemed to be as many on the ground. Don't think there is anything one can do except get your shotgun out.

The chap has brought one of those large plastic owls, the head moves in the wind and are apparently very good at deterring pigeons.

I hate pigeons and have a huge water pistol, bright green and orange, which I shoot at them. They now disappear as soon as they see it - works on the parakeets too.