Suet is hard, white animal fat that comes from around the kidneys and loins of sheep and cattle. It provides a high-energy food source for birds during cold weather. High in calories and easy for birds to digest, suet is particularly appealing to woodpeckers, nuthatches, jays, starlings, and chickadees.
Cardinals, wrens, creepers, kinglets, and warblers also sometimes visit suet feeders. If you don't want these types of birds at your feeder, try a feeder that makes it necessary for birds to feed while hanging upside down.
Suet is an excellent alternative food source for birds during the winter. Plain suet and suet blends are available at many pet and big-box stores. Blends contain things like nuts, seeds, meal worms, peanut butter, and fruit to attract a wider variety of bird species.