Why do birds fight?

Cockatiels could fight for numerous reasons. It could be breeding season and they are fighting over a mate. They could fight over a particular nestbox or could be attempting to chase another bird away from their territory during breeding. A male may want to mate or preen a hen that isn't interested or vice versa. They also can fight because of jealousy if one bird is getting more attention than another. They could be overcrowded in their living space and need more room. The reasons are endless

Cockatiels are like any living creature. They do not always get along for various reasons and sometimes fights occur. Usually however they are nothing more than a lot of noise and wing displaying and neither bird gets physically harmed. If one does however get injured then the offenders will need to be separated into different cages.