The tiels

If anyone out there knows anything about cockatiels I'd like you to contact me. I have my two, Kiko and Chubs. 2 weeks ago I got them a nest box as they seemed like they were getting ready to do their thing. For the first couple of days Kiko (the female) would go in there, hang out, do whatever it is birds do in nest boxes. She would not let Chubs in, but he seemed content to just stick his head in and look around.

Yesterday they started doing something and it's freaking me out. Chubs will not let Kiko near the nest box during the day. He will try to attack her if she tries to go inside. He doesn't appear to be hurting her, just basically chasing her around and nipping at her. But he won't let her anywhere near the nest box. Last night he let her go inside and sat outside whistling seemingly quite happy. This morning he even let her go inside for a while. But all day now he's been keeping her away.

I read that the males will sit on the eggs during the day and not let the female near them. But they don't have any eggs. There is nothing inside the box.

Anyway, if any of you have experience breeding birds please feel free to chime in with any and all advice. Thank you.