Had similar experience several years ago here in Kentucky. The Goldfinch disappearance happened the same spring that I severely cut back my mock orange shrubs which are close to the feeders. I had noticed many small birds used the dense shrubs for cover and suspect my pruning activity contributed to the scarcity of finches at the thistle feeders. The shrubs have grown back and the coincidentally(?) the Goldfinch have returned.We've been feeding goldfinches for many years in our backyard here in Long Island, NY. This year... no goldfinches!! Any expert out there know what's going on?? We miss their happy little twitters!