Rumors have it that when Parakeets are pecking it can mean two things. One it can mean, they are mean to each and so they peck each other. Especially when a female is pecking it is usually a sign of aggression. It can also be a sign of love especially when a male peck a female on her head.
I don't know but my parakeets do the same thing and they are both male. Sometimes they act as if they are fighting with the way they they peck and squawk at each other. I have to holler at them to get them to stop.