rocking

Just wondered if anyone else's cockatiel rocks whilst falling to sleep/sleeping. It's very gentle. We've always read that rocking is always a bad thing or is to do with eggs. She seems really content and is currently asleep so we're not sure why she's doing it? Any ideas?

My family and I adopted a female cockatiel of an unknown age (we were told she was old) about two years ago to join our family of two cockatiels (male and female, unbonded). She has always been a bit withdrawn (story was that she was separated from her mate) so we just let her be and give her...