I had a lone male budgie. I thought of getting him a pair and got a female budgie. Initialy I had them in separate cages for a few minutes ,they seemed to like each other. So I let them in the same cage. They preen each other,cuddle,rub and play for some time but suddenly start fighting. The male budgie attacks the new female budgie out of the blue for no reason. I have a 60x30x35(length x breadth x height format, all in cm) cage. I think the cage is large enough for a pair(because the shopkeeper suggested it for two pairs).I even have two sets of water,food bowls, separate perches and swings for each bird. This male budgie used to show the same behaviour towards a female budgie I previously had, can this be a sign of mental disorder? Please suggest me something.