why are my birds fighting and drawing blood

Question
I have two parakeets, I got them about 6 months ago. they are in a very large bird cage and they have more then enough room...one likes to chase the other all the time. and I felt that they were friends. I was told when I got them that one is a male and the other a female...the reason I got them was because the family that had them gave them up when they had to move out of state.....last night there was a big fight in the cage and one of my birds had blood all around the neck area.....I removed the bird that did this and now he or she (I don't know which is which) is in a different cage..what happened? should I put them back together or just keep them apart and will they get lonely?..they have lots of toys , but being together for so long I don't want them to get lonely...... I was told they have been together for a little over 2 years......and also are mirrors a good ideal for them?..........thanks for the answers................

Answer
I can almost guarantee that the attacker was the female, and the victim was the male.  Females sometimes become very aggressive, especially if they're put in with another male because when they get ready to breed, they become extremely territorial.  I don't know why she suddenly became so aggressive after being with him for so long.  Thankfully this behavior is usually just a phase and after a brief separation, the problem often resolves itself.

I would keep them separate, but close enough together that they can get used to each other.  You should keep them apart at least until the male has time to recover.  Then after a month or so, try putting them back together under close supervision.  There's a chance that she may attack again, and if that's the case, you may need to keep them apart for the safety of the male.

Mirrors are a good idea.  It certainly can't hurt anything.  The worst case scenario is that they will completely ignore the mirrors, but most birds are fascinated by them.

I'm sorry that your bird got hurt.  Hopefully he'll get better soon!