INTRODUCING RATS TO NEW COMPANIONS
                                        Angela Horn (udty075@kcl.ac.uk)
                                        (formerly Angela King)

Normally introducing female rats to newcomers, even as adults, is
fairly easy - although adults will usually have to fight to establish
a hierarchy before they settle down.  However, some females are very
dominant and may attack very young newcomers so aggressively that the
baby is unable to cope with it and is traumatized, injured or worse.
This is very rare, but is probably most likely to occur with older
females which are not used to companionship.  It is still important
that they get a companion wherever possible, but it may take a little
extra effort on the part of the owner for it to work.

Tiny baby rats are not well equipped to cope with the tender
ministrations of an aggressive, jealous strange adult.  No baby rat
should be away from its birth home before 5 weeks and preferably 6.
The age at which you introduce a baby to an adult rat depends on the
temperament of the adult.  If you have just one or two adult rats
which do not show much aggression to the baby, you may decide to
introduce it as soon as you get it.  If the baby is to be introduced
to a large communal cage containing lots of rats, or if one of the
older rats seems aggressive, then you may want to leave it a few
weeks.  I have found it harder to introduce baby rats to adult females
than to adult males; usually adult males do not consider small babies
to be a threat, and will not bully them without good reason.  On the
other hand, some adult females consider baby-battering to be their
favourite sport.  Personally I don't usually introduce babies to the
communal cage (which usually has about 10 girls in it, some of whom
are aggressive) until they are at least 8 weeks old for the following
reasons:

1.  Baby rats need extra high-protein food until they are 10 weeks
old; it is easier to make sure they get their share if they are not
living with too many older rats. 

2.  Babies are sometimes too fragile, too small, or just too silly to
cope with an aggressive older rat.  But by 8 weeks and certainly 10
they should be able to defend themselves adequately without being so
aggressive that they pick a fight with the older rat.

Note that since male rats are often not aggressive to baby rats, it is
better to try to introduce a baby boy to older boys as soon as
possible and NOT to wait until he is old enough to stand up to him.
But if the older boys seem vicious towards him then you may feel that
it is better to postpone the introduction.

TRICKS TO MAKE INTRODUCTIONS EASIER

These suggestions have been gleaned from various sources and numerous
rat owners with far more experience than myself.

1. Rats tell whether other rats are part of their family or social
group by smell.  If you can make your two introducees smell alike, or
at least disguise the smells with which they mark their territory,
then they may not be so defensive towards newcomers.  Dab each rat all
over with something smelly like aftershave or perfume.  Some people
use vanilla essence because it is non- toxic, won't irritate the skin,
and some rats like to lick it off because it tastes nice.  You should
also make sure that the rats are introduced on neutral territory which
doesn't smell of either one - if this is a cage, it needs to be
thoroughly scrubbed to remove all smells of the previous resident. If
you are not introducing them in a cage, but in a room, then make sure
it is a room that the rats don't regularly play in, otherwise the
resident rats will feel\ that it too is their territory.

2.  Some people suggest putting each rat in the other's cage in turn
before you introduce them, so that they get used to each other's
smell.  Opinions are divided on this; I tried it with some boys I
wanted to introduce, but felt that it made them insecure.  Because
they are so territorial, it seemed to worry them being put in what was
obviously someone else's territory.

3.  Often aggression towards other rats is caused by the rat being
scared of the others.  This might happen, for example, if you tried to
introduce a new rat to your resident rats and found that the newcomer
attacked the residents.  This is a sort of pre-emptive strike; the new
rat is so scared that the other rats will beat him up, he is trying to
drive them away before they start.  In this case, you need to try to
relax all the rats involved and keep them calm.  I found that it
helped to have the nervous-aggressive rat on my lap and to keep
talking to him and soothing him, whilst holding him so that he
couldn't attack or run away from the other rats.  Of course, you have
to be careful not to let the resident rats attack the newcomer and
thus confirm his worst fears.

4.  When you introduce a new rat, put a new nestbox into the cage
and/or a length of pipe or a tunnel for her to hide in, or perhaps a
glass jar just large enough for the new rat to hide in.  If the new
rat is a baby, you can get a jar too small, or a length of pipe too
narrow, for the older rats to get inside so that she can hide in there
away from them if she needs to.  The new rat needs a place that she
can feel is her own, or at least where she can defend herself from
attacks by other rats.

With any difficult introduction, do it little by little and stop
before the rats get really tense.  It could take one day, it could
take a month - but the rats will be much happier when they are
friends.

Bear in mind that, whenever you eventually put them together in a
cage, there will probably be some brutal baby-battering from the
resident rat.  It should not go on for long - the worst will be the
first day, and you'll need to stand by to break up fights (spraying
with a plant spray mister full of water is a good way - the rats have
to stop fighting to wash themselves).  Hand out lots of treats, often,
at this stage - anything to distract them from fighting!  It's just a
case of getting them to spend time together; soon they will forget
that they were ever strangers.

When introducing adult females I find it is normally sufficient to
simply dab each rat with perfume, clean out the cage, introduce them
outside the cage and then put them all in the cage together with food.
The more rats you have in a cage, the more fights you will have to
break up (since the newcomer will have to establish her position in
relation to every other rat in the cage).  If you have a large
communal cage, it may help to introduce the new rat to just a couple
of the others in a separate cage first, and let them live together for
a few days, so that she does not have to take on the whole mob at
once.

Normally the first day is noisy, but after two days an amicable
settlement is reached and after a week great friendships are formed.

For exceptionally aggressive rats, a suggested plan of action is:

1.  Put their cages side by side (but not so close that they can reach
out and hurt each other) so their smells become familiar.

2.  Keep introducing them on neutral territory as often as you can,
until either a) they seem to get on OK, or b)the new rat looks big
enough to defend herself (say 8 weeks or more).  During this time,
keep the meetings as brief as possible.  Spray either rat if she gets
aggressive.  You might want to get a pair of thick gloves too!  Feed
them their favourite treats while introducing them if they'll take
them.

3.  When you do go for it, scrub out the cage (if you have 2 cages,
use the less dominant rat's cage) thoroughly, put in their very
favourite food, dab on lots of perfume & bung them in.  Stand by with
the spray bottle, and steel yourself for squeals.  If you see a
serious injury, or think that one is imminent, then separate them and
go for a more gradual introduction process.  Tails often get bitten in
introductions.  It is horrible, but they have to get it sorted out &
unless the newcomer is too tiny to cope, they will sort it out
eventually & will be best of friends within a few weeks.

ANOTHER APPROACH TO INTRODUCING AN OLDER MALE TO A YOUNG COMPANION

It is often easiest to introduce a new male to an older male as young
as possible, so that the older male doesn't see him as a threat.  If
you have home-bred babies, you can carefully introduce one to the
older male for a few minutes a day from about 3 weeks, before finally
introducing them permanently when the baby is older.  If the older rat
shows any sign of viciousness then stop right away.  Baby boy rats
won't normally start to develop a hierarchy of
 dominance before 8-10 weeks, so if you buy a baby rat at around 6 weeks of 
age, older rats should theoretically not be so aggressive towards it because 
the newcomer is not seen as a threat to the incumbent rat.

I have successfully introduced two litters of baby boy rats to four
males aged 6 months.  At 5 weeks of age the adult males met the babies
on neutral territory (I didn�t bother to disguise scents).  The
adult males expressed their dominance towards the babies by holding
the babies down, sniffing them, and generally being quite thuggish.  I
kept a close watch, and decided that the babies were too small to
cope.  A week later, the procedure was repeated.  The adult males
simply sniffed the babies, as if to say '�we remember you!'� and
then played with them.  Soon the most aggressive adult male was being
chased by three youngsters!  For the other litter, the first
introduction went the same way as before, but the second occurred by
accident - the baby boys actually squeezed into the older rats�
cage.  Again, after minor dominance play all got along marvellously.
I feel that I may have been very lucky in these experiences, but even
with more aggressive adult males, repeated short introductions on
neutral territory should encourage the older rat to accept the
newcomer.

Occasionally two well-established male companion rats will fall out
with each other, and possibly become aggressive to humans, as a result
of incresed aggression in reaction to high levels of male hormones in
the body.  The bad behaviour sometimes manifests itself as uprovoked
attacks on other rats or humans.  This may begin at any time after
about 4 months of age, and sometimes as late as a year old.  Neutering
is a very effective way of reducing this aggression: the rat should
become far friendlier to both his cage mate and his humans, and he
will also be less likely to urine-mark his territory.  Neutering a rat
is not quite the same as neutering a cat or dog, so should be done by
a vet experienced in rat care.  Be especially watchful for signs of
infection; a 10-day course of post-operative antibiotics is a good
precaution.

Good luck,
Angela Horn
(Formerly King)