I have two male guinea pigs, one is 6 months old and the other is about 5 weeks old. When I introduce them, they chatter their teeth at each other. What does this mean? And the older one is always mounting the younger one and won’t leave him alone.
When guinea pigs chatter their teeth it is an indication that they are very unhappy with the situation that they have been placed in, and they are unhappy with each other. The mounting is not sexual in nature but simply means that the mounting guinea pig is going to be the dominate guinea pig in the relationship. Or literally that guinea pig is communicating, “I am going to be the top guinea pig.”
If the younger guinea pig agrees to be the less dominate in the setting, he will allow himself to be mounted. If the younger one allows himself to be dominated, he will challenge this position as he transitions from baby to teenager and then again when he is an adult.
Guinea pigs demonstrate this behavior even if they are related. There always has to be a pecking order; if not, there will be war between the two. If neither guinea pig agrees to be submissive, they will hurt each other — perhaps fatally. Death can occur either from injury done to each other in a fight or by the level of stress within the cage that causes eventual death from lack of ability to thrive.
Through observation, you must determine if this is a healthy environment for both guinea pigs. You must observe both now and in the future to insure that the environment remains healthy for both and that they are fully compatible throughout their lives together. Human roommates or family members must live separately if they become incompatible, and the same is true for guinea pigs.