In winter, it seems like some birds just won't hang around your feeders without suet. Some examples can be the Tufted Titmouse, Red-Bellied Woodpecker, or the White-Breasted Nuthatch. Sometimes they stay around without suet, but occassionally they don't.
Suet can be an important part of a birds diet in winter because the main ingredient (rendered beef suet, of course) is high-energy and keeps the bird warm and full. Suet is a favorite among many birds in winter including the Blue Jay, Downy Woodpecker, Red-Breasted Nuthatch, Pileated Woodpeckers, and many others. Even in spring and summer bluebirds will eat suet with berries inside.
If you want to attract more birds this winter, try offering suet and see what happens. I use ROYAL WING WOODPECKER SUET. It seems to attract and keep coming the most species. For more information on bird feeding, go to our 'Bird Feeding' page.