Rat Ear Biting

Question
I've got two pet female rats that I've had since they were rather small. I got them sometime in August from an Uncle Bill's Pet Store. I purchased them out of the feeder rat supply for snakes and have been caring for them since then. That makes them nearly a year old. One of them is an albino, and both myself and our vet believe she is completely blind.

My question is not about the blindness. The albino has always been the alpha rat, frequently power grooming and sometimes nipping at the other rat. Recently, she's taken to nipping at the other rat's ears. The ears specifically. She's stopped nipping anywhere else. I didn't think much of it, but kept an eye on them, and today she drew blood from the other rat's ear. I moved her to the quarantine cage and cleaned up the other rat's ear and gave her time to recuperate.

While she has always exerted her dominance over the other rat, she never drew blood before. She has never shown any aggression towards myself or other humans. In fact, she's napping peacefully on my lap as I type this. I was wondering if you had any clue as to what is causing this behavior, and could offer any advice on how to handle the situation.

I recently had to travel out of town for a week, and left them in the care of my roommate. This was the first time I've been separated from them, and within the week of my return, the ear biting began. Normally I wouldn't think anything of it, but since the behavior started so close to the time of the trip, I thought perhaps I should mention it.

Answer
 Rats with pink eyes always have very poor eyesight, even more so than black or red-eyed rats, and many of them are blind.  This can actually add to the nipping, as they sometimes do it as a defense mechanism when they are startled by something they didn't see coming.

 If she's a dominant rat, chances are she's simply doing it out of dominance.  The ears are a common spot to bite because they stick out and are easier to grab.  Most injuries from rat squabbles are around the face and often under the chin.  If you part the fur there you may be able to find some scabs.

 Unfortunately if this is the case there isn't a lot you can do.  If she were a male I would suggest neutering; I'm not sure if spaying a female can reduce aggression but it's something to think about.  Some rats grow aggressive because they don't have enough room of their own, you may want to look into getting a larger cage, giving them more toys and more things to keep them occupied, or taking them out for longer periods during the day.  Other than that, your only choice is to separate them if the other rat is in danger of being hurt.  You may be able to allow them to play together in an area outside of their cage without problems but if she is going to be mean it isn't fair to have the other rat get hurt.

 Well I'm sorry I couldn't have been more help; aggression in rats can be very tricky and difficult to fix.  Often it never goes away.  When they are very vicious towards another rat the decision to separate them is simple, but with minor squabbles resulting in injuries it can be hard to decide.  My two females fight a lot as well, and one is definitely the aggressor.  Luckily she hasn't caused any injuries but she often pulls at the other rat's skin and makes her squeak and get scared.  Some females are just mean that way, I guess!