American Fancy Rat & Mouse Association

This article is from the WSSF 2007 AFRMA Rat & Mouse Tales news-magazine.

Mouse Keeping: Understanding Mouse Behavior

By Virginia Pochmann

From Mouse Review, Issue No. 9 (July 1989) unless otherwise noted. This newsletter was written for a short time from November 1988 to April 1990, by fancier and breeder Virginia Pochmann of the now defunct Rat, Mouse, Hamster Fanciers (RMHF) club in northern California. Most of this newsletter contained reprinted articles from the N.M.C. News (National Mouse Club in England) but some were original works. Virginia has a background in genetics and husbandry. She worked for several years in biological research at the University of Wisconsin and University of Chicago where she did tissue-culture work using mouse embryos and there learned all about the care of mice as well as their anatomy, developmental stages, and behavior. She did extensive reading in the scientific literature on mice at U.C. Berkeley for several years, particularly in regard to coat color mutations and other genetic factors.

Virginia imported Self Champagnes in 1988, then went to England in September 1989 to attend the National Mouse Club’s Annual Show and to visit fanciers there. She brought back 18 mice (4 bucks, 14 does) which included a trio of B.E. Cream (Ivory in AFRMA), 3 Self Champagnes in Standard and Satin from the same breeder as her original Champagnes, a trio of the extreme Black, a pair of Blue (1 Blue dd, 1 leaden lnln), 1 Argente doe, 1 Banded doe, and 5 Dutch in Black and Blue. [She provided me with my first trio of pure English PEW/B.E. Creams from these litters, Karen Robbins].

Permission given to reprint article.

Many mouse breeders tend to see their animals anthropomorphically. This means that we unconsciously ascribe human thoughts, emotions, and feelings to the animals, as if the animals actually had the same kinds of feelings that humans have. This is in most cases unjustified. We would do better to try to understand the animal for what it is. Only then can we provide for its needs, both physical and psychological.

The mouse has been studied extensively, both in the field (wild mice) and in laboratory settings, and quite a lot is now known about its behavior. To begin, let us look at the mouse objectively. What sort of animal is it? It could be described as a nocturnal, secretive, nesting, burrowing mammal which is small and defenseless and has learned to hide. It tries to stay under cover and avoid the light whenever possible. It lives communally in family groups, and has a highly developed social structure and territorial boundary for each group. We will take a look at how mice react to their environment, to each other, and to us.

The 4 Senses

First, let’s consider the development of the senses in the mouse. The sense of hearing is highly developed. Mice can hear much higher- pitched sounds than humans hear, and most of their communications to each other (squeaks, chirps, and purrs) occur in a range which humans cannot hear. We can study these sounds only through the use of an instrument called an oscilloscope, which records sounds in an ultra-sonic range.

The sense of smell is also very highly developed, and much of the information mice receive about their environment comes to them through smell. They recognize members of their own colony through smell, and reject intruders the same way. They use urine markers to show routes to nests, food supplies, and escape routes. The soles of their feet also have odor-releasing glands which allow a mouse to sniff the foot-tracks left by another mouse, and determine its identity, how long ago it passed by, and even in which direction it went.

Vision is a poorly-developed sense in the mouse. Due to the bulging convex shape of the eyes and their placement on the sides of the head, the mouse can see in a very wide field of vision, but cannot see details clearly. It can detect movement much better than still objects. Experimenters have shown that mice can detect the colors yellow and red. (By contrast, golden hamsters are completely color blind, and guinea pigs can distinguish blue and green, as well as yellow and red.)

Touch is a well-developed sense in mice, as in many other nocturnal animals. Their whiskers are of paramount importance in their orientation, and the long guard hairs in the coat also have tactile function. Whiskers extend forward along the ground as well as out to the sides and straight up in the air, and help the mouse explore its immediate path. They also tell the mouse instantly whether or not it can fit through a small hole. Female mice which have had their whiskers chewed off by a cagemate will often lose an entire litter of young, because they are unable to properly care for the newborns without their whiskers. (Barbered whiskers will grow back within about 2 months. A female with even one-quarter inch of whiskers seems to do alright with a newborn litter.)

The Social Structure

Secondly, let’s examine the social behaviors of the mice within a communal group. All mouse breeders know that males fight each other. In a family group consisting of parents and offspring, usually the male fighting will be at a minimum while the old buck remains dominant. Each colony has a “lead buck.” He will be the only male which mates with the females. All other bucks in the colony are excluded from mating by the lead buck and also because the females reject them. These subordinate young bucks will, however, frequently challenge the lead buck as they grow older and stronger. Such challenges begin with tail-drumming on the ground and stamping of the hind feet. The two bucks may progress to sparring with the front feet, and then to biting in a full-fledged fight. When one male is beaten, he will take up a submissive posture: standing up on hind legs, nose up in air, eyes closed, and forefeet pressed against the body. In nature, the fight is over at this point. In caged mice, however, where there is no escape, the loser may be severely bitten or even killed. A vanquished male without means of escape will sometimes simply die of stress.

Keep the Numbers Odd

(From Issue 7)

In an article by Roger Hutchings from Mouse Fancy Review, Vol. 1, No. 2. “Fallacies of the Fancy” he states, “And now here’s something that everyone in the Fancy doesn’t know these days, although it’s useful knowledge that goes right back to the early days of the Fancy. Suppose you run on a single young buck by himself after weaning. He probably goes off condition before long and may fail to develop as well as his sisters. So you run on two litter brothers until they are starting to scrap, which may be sooner than convenient, then you are back with the original problem. Yes, you can put a waster doe in with a single young buck, but this may not be convenient for various reasons. The simple answer that works nearly every time is that if you leave not two but three (or any odd number) together, they are unlikely to scrap seriously and will probably stay peacefully until maturity. And the explanation? Probably because as soon as two begin to fight another buck chips in and distracts them. Some of Walter Maxey’s neighbours raised game cocks in their backyards and he learnt the significance of odd numbers from them.”


Friendly interactions between members of a communal group include mutual grooming and use of a common nest. During grooming, a mouse will present the part of itself which it wants licked to the partner. It may turn head, chin, or ears toward the other mouse, or may lie on its back to have its belly groomed. Nests are often shared by does with young, and they will suckle each other’s young indiscriminately. This shared nesting behavior has the advantage of keeping the young mice warmer, as there is usually an adult in the nest at all times. (Newborn mice need a temperature inside the nest of 86° F in order to thrive.)

Pregnancy Behavior

Pregnant does will exhibit increased nesting behavior as the day of kindling approaches. Most births take place at night, but not all. A doe giving birth should never be disturbed. The doe may panic when she fears her litter is in danger, running around the cage, carrying young here and there and dropping them. She may become so anxious that she will eat her young if she cannot find a safe and quiet place to hide them. This may apply to the tamest of mice at the time of kindling. The nest and young should not be touched for at least two days after kindling. (Some older females do not seem to mind your snooping in their nests, even right after kindling, but it is always risky to take a chance on your mouse being one of this type.)

The amount of material used in nest-building is directly related to temperature. If several mice nest together and the room is warm, the nest walls may be thin. If the temperature drops, the nest is built thicker and more compactly. Below 50° F, the mice do not feel comfortable anymore, and will try to move to a better place. The darkest and warmest corner is always the chosen nest site.

Facts About Reproduction in Mice

(From Issue 1)

  1. Females housed close to males come into heat at 4 day intervals; this is due to the scent released by the male.
  2. Single females caged away from all males come in heat at 5 to 6 day intervals.
  3. Large numbers of females caged together do not come into heat at all. This is known as the Whitten effect. If then introduced to a male, nearly half of the females will come into heat on the third day. This knowledge can be useful if you need to know when to expect litters.
  4. Mice breed at all seasons of the year.
  5. Some females, if housed in groups, will develop pseudopregnancies. This is called the Lee-Boot effect. In this case, it means that the mice will not come in heat during a 15 day period.
  6. If a pregnant female is exposed to a strange male (not her mate) within the first 4 days of her pregnancy, she will abort the first litter and then remate with the new male. This is known as the Bruce effect. All these effects, Lee-Boot, Whitten, and Bruce, are best seen in outbred strains of mice. Highly inbred (brother-to-sister matings for many generations) mice do not always respond in such predictable manner. (Reference: Practical Guide to Laboratory Animals, by Christine Williams.)

Some Additional Notes on Reproduction

(From Issue 2)

Some fanciers mate up their mice, and if the does don’t look in kindle after 18 to 21 days, the fancier may mate them to another buck. Now, if you consider the effects of the Lee-Boot and Bruce phenomena, you see that if the doe comes out of a group of females caged together, she may well be in a pseudopregnant state which will prevent her from coming into heat for up to 15 days. If she is then bred by the buck, it is too late to provide a visible pregnancy by the 18th to 21st day after pairing . . . and the fancier may assume she is not bred and put her to another buck. The presence of the strange buck will cause an abortion of her existing early pregnancy (Bruce Effect), and we have another delay in breeding results. This can be avoided by leaving each doe with her original mate for a full 30 days before deciding that she is not in kindle.

Extreme Culling & Nest Temperature

(From Issue 18)

It should be mentioned that under extremes of litter-reduction to only one or two babies, the one or two remaining babies may fail to thrive due to chilling in the nest. A nest with 4 babies in it will stay much warmer when the mother is out of the nest than will a nest with only one or two young ones . . . particularly during the first week of life when the young are not yet furred. The interior of the nest must remain at 86° F for the young to do well . . . no matter HOW much milk they have.


Lastly, we’ll take a look at how mice relate to handling by humans. All breeders know that young mice go through a “popcorn” or “flea” stage which begins at about 16 days of age and may last for several weeks. At this age, the youngsters are apt to jump straight up in the air when the cage is opened, and are very escape prone. Some are also prone to bite your hand when picked up at this age. Different strains of mice vary greatly in regard to this wild stage. In my experience, Roan mice and some strains of Brokens are nearly impossible to handle at this age, whereas the large pale Selfs from England do not even go through such a stage. They seem to be born tame. The ones which are wild at this age are apt to leap off your hand unless restrained by the tail, and IF restrained by the tail, are apt to bite! A breeder who has been at this for 20 years taught me that the wildest mice do best if not restrained by the tail when on your hand. When they jump off, you simply pick them up again and set them on your other hand. Eventually, they will stop leaping off into space, and sniff around your hand instead. This way, she avoids being bitten during the training process. Within a few days, they settle down and stop objecting to being picked up. I’ve tried this, and I must say that it works with all but the wildest individuals. Really wild ones are culled from my colony since I don’t care to have them reproducing their bad qualities in future generations.

I’d like to say one word here about training mice for exhibition. You often read, “Mice should be handled a lot to train them for the show bench.” I’d like to amend that statement to read, “Mice must be handled gently to train them for the show bench.” The wildest mice on the bench are not those which have never been handled . . . they are those which have been handled roughly. If the breeder is accustomed to yanking the mice around by the tails and tossing them willy-nilly back into their cages, then of course the animals are terrified of being handled, and will be impossible to judge. The breeder must cultivate an ‘animal-handler’ mentality around the mice . . . which means moving the hand slowly toward the animal when catching it, lifting it briefly by the tail, just long enough to transfer it onto the back of the other hand, and later setting it down in the cage again with great gentleness. Always remember the basic nature of the mouse, which is fearful and timid, and restrain yourself from making quick moves, speaking loudly, and offhand treatment of the tiny animal. Then your animals will be trusting, and will show to their best advantage when being judged.

Training for Show Handling

(From Issue 13)

I was taught a way to set a mouse up on your hand while judging or evaluating it. (It’s easy to demonstrate but hard to describe here.) Hold the mouse by the base of the tail in your right hand and set it on the back of your left hand, then lift it off briefly 3 or 4 more times, setting it right down again each time on your left hand. You do this very gently and quickly so as not to frighten the mouse, and it makes the mouse set itself, and you can see its body shape and ear set and carriage quite clearly while it holds this pose. (Rather like ‘squaring-up’ a dog on the show bench.) I noticed at the N.M.C. Annual Show that several of the five judges there used this technique to quiet fractious mice and make them stand still to be judged. Some strains of mice are just wild and hard to judge, no matter how you try to handle them. These are definitely penalized on the show bench for their temperament. Other strains are just the opposite, and will stand where placed, just like a pointer. Temperament is bred into a strain, just like type and color and size, and must be selected for when choosing breeding animals for your stud.

Handling/Restraint of mice

(From Issue 2)


Most of us routinely handle mice by lifting them by the tails. The tail should be grasped about 1 inch from the rump and the animal not suspended by the tail for any longer than necessary. (If lifted by the tail tip, the skin may strip off the tail.) The mouse is then placed on the other hand for observation. At this point, if the animal is beyond the adolescent stage of unplanned leaps into space, the tail should be released. Animals are much less likely to bite your hand if not restrained by the tail.

When real restraint is necessary for close examination of any part of the body or for medication, the animal should be “scruffed” . . . that is, held by the scruff of the neck between thumb and forefinger.

The tail is tucked under the little finger of the same hand, and the mouse is effectively immobilized. To get the hold on the mouse, lift by the tail and place the animal on the wire lid of the cage where it can get a good grip with all four feet. If the mouse tries to turn back, pull gently on the tail and it will go forward again. Now quickly and deliberately, with thumb and forefinger, take up all of the loose skin behind the head. If you don’t get enough of the skin, it can turn its head and bite. In this position the mouse can be examined at leisure.

Recommended reading on Mouse Behavior:
Mice, A Complete Pet Owner’s Manual by Horst Bielfeld 1984, Grafe and Unzer GmbH, Munich, West Germany.

The Biology and Medicine of Rabbits and Rodents 3d Edition by John E. Harkness and Joseph E. Wagner. 1989. Lea & Febiger Publ. Co., Philadelphia, PA. ISBN 0-8121-1176-1. [Latest edition published in 1995. KR] *

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Updated March 30, 2015