Aggresive behavior

Question
Hi, I got a guinea pig in Feb this year (Guinea) and I recently got another one so he wouldn't feel lonely when I couldn't give him enough attention. The latest one (Houdini) was small and they got along fine for some months. Now Houdini is older and bigger and just a moment ago Houdini started displaying aggressive behavior towards Guinea. He was nipping his butt and they reared up at each other and then Houdini started chattering his teeth and they both leaped at one another. I jumped up and intervened but I'm worried they will continue with this and I won't be there to stop them and they might hurt one another. I don't know if they would have started drawing blood if I hadn't stopped them. Should I separate them or will they work it out on their own?

Answer
What is happening is Houdini is reaching sexual maturity and is driven by hormones. Would they have drawn blood on one another, absolutely. You need to separate them and leave them apart.

Don't ever put your hand in harm's way by trying to break up a fight. The best way to break it up is using a garden glove. Don't put it on your hand, just grab it by the end and smack them on the head to get their attention away from each other. I don't mean to try to hurt them, just pop them with the glove and it will break the fight. One or both of them may turn their teeth to the glove, which is why you don't want it on your hand.

Guinea pigs are herding animals, and like all herding animals they run on instinct. This applies to any herd of any species. The herd consists of primarily females. The only males allowed to stay are the young ones that need their mother and have not reached sexual maturity.

The alpha male maintains breeding rights to the herd of females. In some herds or packs such as wolves, there is only one alpha female that is allowed to breed. This prevents inbreeding. With guinea pigs the only males in a herd that will be allowed to remain are those who pose no threat to the alpha male.

Once a youngster starts maturing and his hormones begin to kick in he will start to challenge the alpha male. This applies even though there are no females present. They start to fight over breeding rights. If the old male maintains his status the younger is banished from the herd. If the youngster wins the battle the old one goes away. That's just the way nature has made them.

They are hard wired for this behavior and there are only rare exceptions:

Old males that have passed their breeding age will accept a younger one without a problem. Again, it's only because there is no challenge.  In your case you have two males that are still going to battle over the females, even though there may be no females present. It's just a hormonal reaction and not something you can change.

Chattering teeth is a warning that a serious fight is imminent. The fight may end in the death of one or the other if not broken up. Serious wounds end up in bad infections. The only choice you have is to keep them apart. You can put their cages side by side, but you cannot allow them to be in the same cage together. As long as there is a barrier between them they will be happy.

I hope this answers your question.