Are apples good for your bird? Yes, they are and contain the following:
Lurking in the seeds are danger for your bird. They contain poison, in the form of amygdalin, a cyanide and sugar compound which can be broken down in the body into the highly poisonous compound hydrogen cyanide. However, the amount in an apple seed is tiny, not enough to cause harm to a person but in a bird it will as they are much smaller bodied than we are and so it takes a much smaller amount to be dangerous or even lethal for them.
Apple seeds if swallowed whole are not harmful at all as the seed passes through the body unnoticed and intact the danger occurs when they are broken open or chewed to release the harmful cyanide.
Because a bird will crack open a seed to eat it this makes apple seeds very dangerous for them and always wash all fruits well to remove harmful pesticides that may be present.