age. Except for sexual behavior and fighting, their activity is essentially adult behavior.
Sexual maturity is reached at the age of 2 to 3 months.
a. Young rats and mice gradually become familiar with their surroundings,
undergoing a "training" period in company with their mother. Their first trips away from
the nest are often by accident. Nursing young, clinging to their mother's nipples, are
sometimes dragged from the nest as she leaves. Later, they may follow her for a short
distance when she leaves the nest. This habit of following increases until finally they
regularly accompany her as she goes about her normal activities. During this period,
they learn their home area by associating with and imitating their mother. However,
there is no evidence that she consciously tries to teach them. They learn by imitation
and experience, part of the latter being gained when they accompany each other on
forays. By the time the youngsters are 3 months old, they are very active and are
completely independent. This level of activity remains high until they are about 9
months old, when old age overtakes them and they slow down.
b. There appear to be certain daily patterns of activity among rats and mice.
When food is abundant, the rat shows the greatest activity during the first half of the
night. A number of studies showed that the rat becomes most active at or shortly after
dusk and that this activity continues until about the middle of the night. The house
mouse shows a similar pattern of nocturnal activity, and in addition shows a second
lesser activity peak starting well after midnight and lasting until dawn. This latter may
also be the case with many rats. Superimposed on this nocturnal activity are short
periods of restlessness and activity occurring every few hours throughout the day and
night. These shorter activity periods are related to periodic stomach contractions in the
rat. The major pattern of nocturnal activity breaks down, however, when the individual
is hungry. In one experiment, the amount of available food was cut below the daily
needs of caged rats and mice. They quickly shifted their peak of activity to the period
when the food was added to the cage. Even when it was added during daylight, they
were most active at feeding time. These habits of laboratory rats appear to hold true in
the field. There is some conflicting evidence from the field on house mouse activity. On
a Maryland farm, more house mice were trapped during daylight hours than at night. It
is possible that this daytime activity was related to the absence of cats and other
enemies on the farm. Then, too, much of this daytime activity was in the relatively dim
interior of barns.
c. Knowing where rats and mice are likely to go is important in such procedures
as ratproofing. They like to use regular paths or runways, especially along walls or
objects that present a vertical plane. When a rat or mouse wants a piece of food, it will
run under and behind things until it gets as close to the food as it can. Then, if the food
is in the open, a short dash is the only exposure to danger. The farther away from
runways that traps or baits are placed, the less is the likelihood that they will be visited.