Big Garden Bird Watch - feeders V tables

Having done the BGBW today the numbers of birds in my garden is well down on previous years, especially the sparrows. However, the birds seem a lot more timid this year and I can't understand why. I have a row of about 8 seed feeders under the eaves of my garage and most years these are VERY active with groups of up to a dozen sparrows or gold finches swooping across from the trees. This year during the hour of my survey not one bird visited the seed feeders and none of the fat blocks either. All of my visitors were on the bird tables or the tree stump in the bottom border that is baited with loose seed, peanuts etc.  I am puzzled as to why all the garden birds seem to have gone off the feeders and seem to want to keep clear of the house. Nothing has changed with my garden arrangements and the only thing I can think of is that maybe a sparrow hawk has "spooked" the locals into not using the feeders.