An imbalanced or incomplete diet is a common problem with pet birds, and is a relatively common cause of illness. There is a lack of scientific study on avian nutrition, especially as it relates to the different species. While our avian nutrition is still in early stages, most experts agree that a good diet for parrots begin with a formulated diet with a variety of other foods added as supplements. Lories and lorikeet have special needs, and are discussed later in this article.
For most pet birds, especially parrots and parakeets, a diet based primarily on seeds is deficient in many nutrients, including vitamin A and calcium, and is too high in fat. This is not to say that seed do not have a place in avian diets, but many birds come to prefer them to the exclusion of other healthy choices and can be fussy when it comes to trying a varied diet. Some birds will even pick out a couple of favorites from a seed mix, which further reduces the nutritional balance in the diet. When it comes to parrot nutrition, consider seeds to be somewhat like junk food: birds love them, but they are not the healthiest choice. Form most species of parrot, seeds should only make up about 10 percent of the diet. Some species, like budgies and cockatiels are naturally seed eaters and can tolerate a higher percentage of seed in the diet, but even for these birds, seeds should only make up about 25 percent of the diet.
A number of years ago, realizing that many parrots were suffering from nutritional deficiencies, companies began producing pelleted diets for pet birds. These are made from a variety of foods including grains, seeds, vegetables, fruits, fortified with vitamins and minerals, and are baked into pellet or variety of other extruded shapes. These provide a balanced nutritious diet and prevent birds from picking out their favorite food items and leaving the rest. However, many birds, especially those started on a seed based diet, do not readily take to eating a formulated diet. As well, formulated diets, though well balanced, do not provide the variety and stimulation that many pet birds crave in their diets (after all, eating the same thing day after would be boring for anyone). Therefore, pellets can be considered the "base" of the birds diet, comprising 50-60 percent of what the bird eats.
Some good brands of formulated diets include Harrison's, Zupreem, Kaytee, Pretty Bird, and Roudybush. As these diets grow in acceptance and popularity, manufacturer's are producing lines formulated for particular species and also for health management (e.g. lower calorie diets for weight management). As mentioned earlier, these diets come in a variety of shapes from larger chunks down to crumbles, and you may need to experiment to find the type your bird prefers. Some birds, especially those used to a seed based diet, may be difficult to switch to a formulated diet - advice on switching is available in "Switching Pet Birds from Seeds to Pellets". If you are in doubt over which diet would be best for your bird, consult your bird's veterinarian for advice.