As rats are sociable animals, no matter how much attention you give them, they will be happier if they have a (same sex) friend or two living with them.
Obviously, the best way to do this is to get your rats from the same place at the same time. However, where this is not possible, you certainly can introduce a ratty friend at a later date.
Females are generally easier to introduce than males and the younger the better. While young males up to about 10 weeks age can be introduced easily, older males can be more difficult as it is in built to defend their territory. However, that does not mean it cannot be done – you just need to be extra vigilant when making introductions.
Where you have a young, lone female you should have no problems introducing a friend at all. However, you should always have a spare cage ready in case the pair don’t hit it off immediately. Also, when introducing older rats, it could take up to a couple of weeks so it is a good idea to have a spare cage.
When introducing rats you need to set aside a good chunk of time so that you can supervise the introduction and then see how they get along.
First of all, the introduction will be made easier by reducing or masking the rats’ natural smell. A dab of vanilla essence (the type you use when baking a cake), on both the rats backs will help neutralise and dominant odours.
You then need to introduce them on neutral territory – this should not be somewhere where the resident rat plays. (You can try the bath, or your bed for example). In cases where you are introducing youngsters (ie up to about 10 weeks of age), this may need only one introduction. In the case of older rats – either where you are introducing one to another older rat or an older rat to a youngster or where you are introducing an individual to a group, or where you – this will normally need several introductions before they can live together happily.
If you have two youngsters, you could also try using your lap (seated on the floor) as the neutral ground. This will show the resident rat that you have already accepted the newcomer as well as make both of them feel safe.
The introduction process may be several short ones or one long one – it really depends on the rats and their personalities etc. It may take an hour, or three intros over the course of a day or even an hour playing together every night before they are ready to share a home.
If at any time the rats fight and blood is drawn or fur is pulled out, separate them immediately. Leaving them together could cause serious injury, or even death. And never introduce a youngster under 6 weeks old to an adult as there is a risk that they could be killed.
You can expect a small amount of squabbling as they decide who is ‘the boss’ and also excessive grooming, but this is natural, as well as a few squeaks. If things start to turn serious, spray them with water from a plant mister to break up the fight.
These sort of squabbles tend to resolve themselves over time. However, if there is real aggression, you must split them up (make sure you wear thick gloves). Sometimes the ‘new’ rat will be scared and so strike out at the resident rat without even thinking.
If they get on well straight away (which often happens with youngsters under 10 weeks old), leave them to play for a while. Let them share the same food bowl, ensure that they have plenty of water and also make sure they have somewhere that they can each retreat to (such as an empty wine box) in case they get scared.
Some rat owners make intros easier by putting something like a blob of baby food on to each rat so that they have to get to know each other quickly by grooming and cleaning each other!
If the intro carries on going well (which will involve a lot of sniffing bottoms and play fighting as opposed to ‘real’ fighting and then both of them sitting happily together) then you can move on to the next stage and let them move in together.
Make sure that the cage has been thoroughly cleaned as well as the food bowls, toys etc so that the cage still smells ‘neutral’. Use new bedding and hammocks. Watch how they react to each other and certainly keep checking on them to make sure that they have not started fighting (that is why it is good to do introductions when you are not working so that you can keep a close eye on them).
If they don’t hit it off immediately, then put both the cages next to each other so that they can familiarise themselves with each others smells etc. Then try again the next day. Swap toys, too, to mingle their natural odours which will make them more accepting.
By being patient with the introductions, unless there is real aggression, your rats will soon be happily living together.