They are needed in small quantities. Deficiencies cause membrane defects seen as poor skin and feather condition. There are three essential fatty acids linoleic, linolenic, and arachidonic, that must be incorporated into bird diets. Vitamins - Vitamins are needed for healthy skin and bones, fertility, growth, and healthy blood, muscles, and internal organs. They are essential for proper bone and feather growth as well as normal neurologic and cardiac function.
Seeds are deficient in calcium.
Iodine - Needed for thyroid function especially for parakeets. Trace minerals - zinc, copper, iron, selenium, etc. These minerals are needed in tiny amounts, but the body cannot function normally without them. All-seed diets are deficient in trace minerals. It may take several years for a deficiency to actually make a bird clinically ill.