My neighbour feeds the birds (primarily pidgeons), and squirrels. Both species have taken advantage of the free food and gone forth and multiplied. The extra pidgeons attract hawks (bonus), and the excess squirrels come over to my garden to get their salad fixings. With this long, hard winter, the squirrel damage has been extensive. 
Normally, I don’t do anything to the lilac until after it blooms, but when I saw how all the stems/twigs closest to the fence had been chewed, I figured I better clean them up ASAP. So I took out the worst of the damage, only leaving one of the longer stems that had potential flower blooms on it. 
I may take that out later. There is still damage on the main stems from previous years, (the closest large stem to the right-hand side of the photo to the left is the most obvious) but if I took it all out there would be very little lilac left.
Well, I was quite pleased with my early intervention. About a week later, though, I turned to look out the window just in time to see the southern most branch whipping back and forth, and a squirrel sitting innocently on the fence nibbling on his (or her) purloined treat. Later inspection showed that the squirrel had moved on from chewing emerging buds off the plant, to tearing off strips of bark.
Deep Sigh. I am now contemplating giving up removing all the suckers that come up from the base every year right in the middle of the garden, and instead let a few of them get established so that eventually I have a new lilac bush that is not so close to the fence. However, I was watching an extremely acrobatic squirrel dashing around the young elm I am trying to get established, and I’m beginning to think that even if it were further from the fence it would still get marauded. Apparently the squirrels favourite food is whatever I have only one or two of – plants that I have large numbers of they aren’t interested in.
pruningdiaries 