Black oil sunflower seeds in shell.
Black oil sunflower seed is a great source of quality protein, vitamins and minerals. The black oil seeds (“oilers”) have very thin shells, easy for virtually all seed-eating birds to crack open, and the kernels within have a high fat content, extremely valuable for most winter birds. It has particular high quantities of thiamine and niacin. It's main mineral ingredient is iron, which is a difficult nutrient to obtain in sufficient quantities. It also has anti-inflammatory properties.