Although pelleted commercial diets are usually considered a good nutritional foundation, experts disagree on the need for supplements. Some experts believe supplements are not necessary, and that a pellet-only diet is best for most birds.
Many others feel that a variety of supplements help round out a pelleted base. The ideal supplement, if any, depends on the base diet as well as the species of bird.
For more information, please read the story Should You Supplement Your Bird's Diet.