I thought it may be handy to have a sticky on typical dominance behaviours for a reference - hopefully it may help humans understand guinea pigs and their behaviour a bit more and hopefully prevent some avoidable problems! Below are listed types of behaviour and possible reasons to help determine what may be happening and possible solutions - is it a proper fight that can result in an awful ending, or just normal and usual dominance behaviour? Obviously this is a guide and not law, but it may help identify issues and offer likely causes and suggestions that may help. Normal Dominance/Getting-To-Know-You Behaviour: These types of behaviour can include: Bottom wiggling, raised fur or hackles, hip swaying Purring or quiet/low rumbling whilst doing the above or sometimes without the movement "Nose offs" - not necessarily aggressive, it's just like teens squaring off to each other and swaggering a bit Bottom sniffing and cheek to cheek rubbing - scent glands are situated in these areas, so these will be popular! Dragging the bottom along the ground (a bit like territory marking) Mounting (from all angles - head, side and rear!) and chasing or chasing and mounting combined Mild teeth chattering (fairly quiet chattering, almost like they are munching loudly on dry food or hay just with a bit more volume, but NOT the loud clatter for aggression, see below) Warnings / Getting irritated and more serious: If one or more pigs are snorting, (a bit like a quiet sneeze or a puff can mean extreme irritation), stressed squeaking with increased volume, head bobbing nose offs accompanied with very loud teeth chattering and slight raising up on back legs, yawning to show the teeth and/or giving narky little nips, kicking out and/or wee squirting, then I would be watching very carefully and get ready to distract them as they could be about to have a fight. Serious aggression/fighting: If the above events do not calm down fairly quickly, this can escalate into the pigs lunging or pouncing at each other, loud rumbling, obviously vicious bites rather than nips, a concentrated mixture of most of the above warnings (snorting, obvious rearing up on their haunches as if rearing up to fight, raised hackles, loud rumbling, yawning and loud teeth clacking - this noise is unmistakeable), and will likely result in pigs causing serious damage to each other - the pigs will have to be separated immediately. Never put in your bare hands to separate fighting guinea pigs, always have a towel handy to throw over them as those pigs will not realise or care that your hands are getting in front of their teeth and can result in really nasty bites. Oven gloves will also come in handy! Submission: Loud squealing as if in pain (but not being in pain!), running away or standing very still. So what may cause this type of behaviour in boars? Stroppy age? Are they at the stroppy hormonal teen stage (anything between on average 3 months to 15 months)? If so, they may just be testing for dominance. This can go on for a while and will need monitoring, but usually settles down eventually. Time of year perhaps? Spring can invoke all kinds of ancient instinctive behaviour when the weather starts to warm up, the hormones start to get going and the boys are looking to strut their stuff. This can often result in increased normal dominance behaviour and lots of rumblestrutting and mounting to prove to all around that they are men and they are feeling good! Also, the heat of the summer can sometimes get to them, resulting in bad tempers and frustration as they are hot and uncomfortable, and may start squabbling with their cagemate. Another reason to keep your guineas as cool as possible during the hot months! What else can trigger them to fall out? Other things that may set them off are being near females, lack of space/not being able to get away from each other, change of environment, illness, bullying or simply the teenage hormones kicking in. If you suspect an illness may be causing behavioural problems, please make a vet visit. Possible ways to avoid a fall out: Loads of space, as much as you can spare. Try a C&C cage, plenty of examples can be found in the Housing section of this forum. Two of everything - including dry food bowls, wet food bowls, water bottles, toys, hidey-holes, tunnels etc. Bathing can often help, but make sure you use the same shampoo for both pigs! If you have females, try and keep them at distance from the boys if you think it may be this that is causing the problem - if the females are in a completely different area, try and handle the boys first before the girls as the smell of females on hands, clothes, items or faces can set them off too. Hay is often a good distractor as well. Try a DAP (Dog Appeasing Pheremone), these waft calming pheremones over the pigs which can help them to calm down. It must be the dog one though, not the cat one. If they are still squabbling and looking like they are really getting on each other's nerves, try a trial separation with a mesh divider - quite often a few hours "time out" can really help them calm down, but try not to leave it too long before you try them together again. Of course, sometimes they may just not be able to get along and simply don't like each other! Sadly, there is little that can be done about this, and if they look constantly stressed even if they are not seriously fighting, it's worth getting their health checked and then reconsider your options with them. When do you see these behaviours in sows? When bonding sows with other sows or neutered boars, they need to accept each other first. If that initial acceptance doesn't happen or if the hierarchy cannot be settled to every piggy's satisfaction during the following dominance phase, it can come to aggressive behaviours and even to scuffles or full fights with bites. Some sows can develop hormonal problems (ovarian cysts) as adults and become rather aggressive towards their companions. In this case, you need to seek help from a preferably expert small animal vet. There is now a wider range range of treatments available than just a spaying operation. What can trigger fall-outs? Very often fear is at the bottom of aggressive behaviours. Guinea pigs are out of their depth in unfamiliar surroundings and with unfamiliar guinea pigs. If possible, give new guinea pigs a few days' time to settle next to their prospective friends, so they are used to where they are and to who they are going to meet; that will cut down on the general stress level in a bonding. Another trigger can be feeling stuck and crowded in a tight corner with no safe way out. Please never use hideys with only one exit during the introduction and the immediate dominance phase. Also avoid any nooks and crannies that guinea pigs could try and hide. You can construct temporary "tents" with tea towels or big hankies that are pegged to the cage bars for that purpose or use open log tunnels once you transfer the newly bonded guinea pigs from the neutral outside area into their cleaned and rearranged cage. The top spot can be decided in a series of sometimes very tense face-offs which can display some of the "ready to pounce signs" if the guinea pigs are very closely matched in daminance. If the piggies are staying within the limit of just threatening and then just walking away, let them get on with it, otherwise, separate immediately (towel/glove at the ready!). Something like this is a difficult bonding that can take time to work out and that can sometimes fail at a later point when the piggies in question fail to come to an agreement. Please accept that especially dominant guinea pigs don't just like every other guinea pig and get on with it. They have instant likes and dislikes, the same as we humans. Don't try to make a bonding work after a major scuffle; it usually won't work! Once guinea pigs have made up their mind that they don't like another one, they are not going to change their mind! More on bonding, social behaviours and dynamics and problem times in these links here: Illustrated Bonding Behaviours And Dynamics Introducing And Re-introducing Guinea Pigs Boars: Bullying, Fighting, Fall-outs And What Next? Sow Behaviour Boars: A guide to successful companionship.