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Mouse behaviour

Behaviour in the mouse

We have all heard that the mouse is a social animal, but what do we really know about their ways? Mice act different in captivity from how they act in their natural environment. Some behaviour that we see in our pet mice is the same as those you could see in wild mice - but not all.

Behaviour in the wild

Wild mice are both territorial and social. Generally speaking they show territorial behaviour towards individuals of the same sex, and show social behaviour towards individuals of the opposite sex. The male mouse has a larger territory than the female mouse. The female mouse takes up territory inside the territory of an established male, and the male is welcome into her part of his territory. Some males have more than one female living inside his territory, and the females each has their own territories inside his territory that the male visits at will. Females defend their territory towards each other.

Behaviour in captivity

In captivity we do not see that much of the territorial behaviour in female mice, many females live happily together in packs. Any breeder of mice might tell you that if more that one female has a litter of about the same age in the same cage they often put all the babies in one big heap, and share responsibilities. They take turns feeding and caring for all the babies. Any older female in the cage usually helps out with the babies. Usually they give birth in their own corner of the cage and keep the babies for themselves the first day or so, and then they actively carry all the babies into one big heap. So you can say that most females show social behaviour towards each other in captivity, which is not their natural behaviour. This means that the female mouse in general already has changed its behaviour through living in captivity for many many years.

The males on the other hand are often true to their normal behaviour and show territorial behaviour towards other males. It is important to realize that these males are still social animals and need the company of at least one other mouse; it is just that males are created to live happily with at least one female, not with each other.

One behaviour that you easily can see in pet mice is that the males often helps out with the babies, especially if he lives together with just one female. (If he lives together with more than one female they help each other.) He may lie on top of the babies to keep them warn while the female is resting or eating. I have seen no report of this behaviour studied in wild mice, but since it is very common in captive mice I can guess that wild males help out with the babies too.

Female mice living together may squabble but it is extremely unusual that a male and a female living together don't get along perfectly. On the other hand it is well known that a lonely mouse in a cage is a sad individual, health wise impaired. Many studies show that this is the case. Since we cannot just let all male mice have a female mouse each - that would make too many mice everywhere in no time - we have a problem.

Lonely mice is a problem

As we have seen, mice are not born to live alone; they need daily social interactions with members of their own species just as any other social animal. It is mainly male mice that are kept alone, but this sad fate happens to a few female mice too. A solitary male mouse in his lonely cage suffers just as much as a wild mouse without a female, the difference is that the wild mouse can go out and look for a female. No mouse is happy on it's own.

The problem with lonely male mice arises because mice are created to produce as many new baby mice as possible. Just think about how many different species of predators that eats mice. In the wild male mice don't have time to socialize with each other; instead they use their time to eat and to produce new babies. In captivity males don't have to make new babies all the time any more. Male mice are not suited to live in captivity unless we who own mice really make an effort to make our males' lives happier.

What is done about lonely mice

Some male mice in captivity actually can live happily together and share a cage without any signs of fighting, and this has been known a long time. Already when I started breeding mice almost 25 years ago there was a few male mice around that happily shared a cage without fighting all life. I happened to have such a strain in the early 1980s, of black tans with white markings, where many males never fought. In the laboratory many strains of mice with males that never fight are known, my first pet mouse Aristoteles was such a laboratory mouse. Aristoteles was from a strain where 100 % of the males never fight. There also many laboratory strains with males that fight violently and kill each other if they can at an early age, some younger than three months. Many English type mice are known to be able to live together without fighting, but far from all. Here in Sweden we have breeders who keep Swedish type together without fighting.

This is not common practice anywhere that I know of, but some mouse breeders castrate those of the males that they are not planning to use for breeding. I have been informed that an intact male will often accept a castrated male. I have no personal experience with this, so I don't know how that works out.

A more common practice among breeders here in Sweden is to place an elderly female in the cage of a lonely male mouse. As long as the female is old enough not produce babies this is a perfect solution for the breeder, and such a pair will always thrive and live happily together. The only problem with this is the shortage of elderly females. They are very useful, both as company for younger females when having babies as well as company for a solitary male mouse. If you happen to own a female that is sterile she will do just as well as company to a male. But sterile females are scarce. And this does nothing to produce a solution for male pet mice, breeders generally use all elderly or sterile females available and the pet owner's males will still have to live alone or fight to death.

Males together

Keeping males together is not as easy as one might think. If the males really like each other and don't fight at all you might have the luck to witness really happy males sleeping together and share a cage without ever showing any signs of aggression towards each other. Not fighting, not threatening each other, just seems to have a good life. There are cases where males live like this all life, without ever even having a grudge. Don't forget that this is not the normal natural behaviour, and that mice can easily revert to fighting at any day, so make sure to have extra cages around just in case.

If you ever get such nicely behaving males there are a few things to consider. If you ever take them apart at all the chance of them to start fighting is bigger. Whenever they start fighting it's over, and you must separate them immediately, or they might kill each other. One problem occurs when breeding, often if you take out one of the males for breeding they will not accept him back again. You can try to house him with his own sons instead. The remaining males in the original cage usually don't fight among themselves after one has moved out. If you want to take one of the males to a show, you must always bring the whole cage with you, and they might still fight just because of the smell of strange males at the show. They can start fighting one day, without you doing anything, and you must take them apart. The slightest bite wound is a sure sign that someone must move out from the cage. Usually it works best to only have two males together, or at least not more than four.

If they start fighting it is very important to take them apart at once, they will never stop fighting once they started, they won't decide who is the leader or anything like that, they just will never be friends again. I have no personal experiences of putting older males together; the oldest pair I did put together was 3 months old and an adult male that had never met. That went well until the older male started having health problems, then they started fighting and I had to separate them. The normal practice here in Sweden to leave litter brothers together for as long as possible, and to put in sons to their father. Even if they live happily together for 9 months or a year they might very well start fighting any day. Once they start fighting you must take them apart, anything else is cruelty to animals.

Few pet owners have males together, it is mainly breeders who do, and they probably like the idea of not having as many cages. Among breeders some are breeding mainly from males that will live together. Except from being practical we do it for the sake of the mice, in order to avoid the problem with lonely suffering mice. It is well known that a lonely mouse is sicklier and suffers from being alone. We usually try to breed from males that are more prone to accepting the company of another male in his cage. I have done that for many years myself. Today more and more breeders seem to get the idea. As long as the breeders always have the sense to take apart any mice that fight, it is a very good thing for the mice I think.

If you are a breeder and want mice like these you can probably buy some from another breeder. If you do buy an established group you might find that they will fight when they move into your mousery. Don't be discouraged by this, it is the smells of strange males that is the cause. If you do mate with these males, you might get babies that will live together as adult males, if you try to let the male babies stay together as they grow older.

Written by Eva Johansson, 2004.