Well said, this is the bottom line really, that there is absolutely no way to know if two birds will get along or not. I too would never, ever recommend keeping two birds in the same cage, even though some birds get along nicely outside of their cages they can become very territorial inside their cages, plus some birds get along well and then all of a sudden they fight and one of them gets hurt, or worse. So no matter what bird you get you'll need two different cages and you'll need to introduce them slowly and supervise them. It will take time for them to get used to each other, it's a slow process at times. I also agree that you definitely do not want a male-female cockatiel pair unless you want to breed them.A male would get along with a male but not all birds get along. My cockatiel and budgie have got along, and they are both males. But my lovebird doesn't want to get along with them, but they want to get along with her.
It doesn't really matter the gender, it depends on the birds.
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