Male does not allow female to sit on eggs
Male kicks off the female out of the nesting box and doesn’t allow her to sit on eggs. He’s aggressive when ever female comes near to the nesting box.
You didn’t mention the species of bird, but this is not uncommon behavior with cockatiels, especially. The most important thing is that one of the birds is sitting on the eggs around the clock. Pairs will often take turns. Sometimes the male or female will seem to get confused or get too territorial and will keep the other parent away. You may have to remove the male part of the time to give the female a chance to sit on the eggs. If you split them up completely, it will be very hard for one bird to take care of the eggs and any chicks alone. So unless there are feathers being ripped out or blood being drawn, some sparring or harmless fighting is fine. The male might settle back down after being removed for a few hours. You will just have to keep an eye on this pair and keep intervening when necessary. If this is their first clutch, it may fail anyway as first clutches more often do fail. You need to rest the bird between clutches, for a few months, so possibly as they get older and get more practice, the will do better as a pair. But some pairs do not make good breeders, so you may end up needing to split them up for good in the future if they don’t improve.
Thank you for asking Lafeber,