Suet

In the bird feeding world, suet is considered the nutritional substitute for insects during the colder months. Officially, suet is the internal body cavity fat from cows (primarily kidney fat). Many people like to make their own suet and have their own special formulas they take great pride in. From my perspective, I view suet as a way to provide missing nutrients for certain birds all while attracting them to my yard for my viewing enjoyment.