This has been a great day for birdwatching.   I was sent home from work because the hill where my office is located began to ice over and the snow created a frenzy at the feeders.   There was also a first time visitor to the suet and a bird I have yet to identify.   It was about the size and shape of a mockingbird, but several shades of gray darker about the color of the catbird.   Its tail was as long as the mockingbird but dark in the middle with long white feathers to the outer edge. Any suggestions?