Unfortunately, many owners fail to feed their birds correctly. A seed diet is not adequate, but is high in fat and deficient in vitamin A, calcium and protein. Eating nothing but seed is like eating nothing but margarine on bread. In addition to feeding your bird seed, you should also include in its diet a variety of vegetables, fruits and pellets.
When supplementing your bird's diet with other foods however, it is important to know which ones can be harmful to your bird so that you can be sure not to accidentally feed it to him. Below is a sample list of foods to avoid. Please note that this list is incomplete. If you are ever unsure about a food, please ask a vet or some other person who has avian experience. It is always better to be safe than sorry.
Most unsweetened breakfast cereals are fine. The ones you need to avoid are the sugary types. Sugar in general doesn't have any nutritional value, just calories.
Lettuce is mostly water and will only give your bird diarrhea.
Avoid milk as birds are lactose intolerant and may get diarrhea.
Chocolate is very TOXIC and can make your bird very ill or cause death.
Again, TOXIC and FATAL.
SEEDS & PITS
Like the seeds of apples and pears or the pits of peaches and cherries. These are TOXIC and FATAL.
NUTS & PEANUTS
Should be given on rare occasions due to the high fat content.
Again, where sugar is concerned try to avoid such.
GRAVEL & GRIT
Many people do not realize this but most birds DO NOT NEED gravel and grit in their diet. Their gizzards are well equipped to grind food quite efficiently. Grit can be dangerous because ill birds may gorge themselves on grit and block their digestive system. In general, the only birds who really need grit are softbills (like canaries and finches). If you're not sure... ASK YOUR VET!
Always give your bird fresh water daily. If possible, try to give your bird fresh water twice a day, like in the morning and at night. Many birds have a tendency to accidentally poop in their bowls which can lead to the harvesting of harmful bacteria and can cause your bird to get sick.
Vitamins added to water can go bad quickly and encourage bacterial buildup. Instead, sprinkle a powdered bird vitamin/mineral supplement on moist foods occasionally to help avoid deficiencies.
Do not give food that is spoiled, salty, greasy, containing alcohol, or sugar.