rabbits in heat?

Question
I have 2 rabbits, they are almost 4 months old. I took them to the vet and we believe they are both girls.  They have become very aggressive towards each other.  Is is safe to leave them together and is this a sign they are in heat?

Answer
Well, they are the right age to start entering puberty.  If they fight all the time or frequently show aggressive body language, you should separate them until you can get them spayed.  Rabbits can get very territorial when they start becoming of age sexually.

Aggressive body language is is ears back, tails up, in a posture that indicates someone wants to fight.

If one rabbit is mounting the other, this is a sign that the rabbits are trying to work out who is going to be the alpha.  This is OK, unless the rabbit being mounted starts to get annoyed with it because it goes on too long.  Then you should intervene.  You might also see that one or both rabbits start using poop pellets and urine to mark territory.  This is something rabbits will use as they go through the process of working out who is top bunny.

But your first step should be to get them spayed.  It will take about a month for the hormones to get out of there system.  Then, the rabbits will either get along again, or you may have to use some techniques to help them along.

This link, gives some tips on what one person does to bond rabbits:
http://www.rabbitnetwork.org/articles/bond.shtml

And if the going gets a little rougher, there's some more info out there with at this site:
http://homepage.mac.com/mattocks/morfz/rabcare.html#bond