Relationship of Activity and Aggression to Density in Two Confined Populations of House Mice (Mus musculus)

Abstract

Two separate populations of house mice (Mus musculus) were established by placing two sibling females with one sibling male into each of two cages. Food and water were provided ad libidum and nest cans and materials were made available. Daily checks were made for births and deaths. Observations of behavior were made during 10-min intervals between 8:00 am and 8:00 pm at various times of the day. The number of mice active and number of attacks and aggressive chases were recorded. From the data gathered, an activity rate and an aggression rate were calculated. In both populations activity rates showed fluctuations with a decreasing trend with increasing density in one population. Aggression rates in both populations fluctuated cyclically with a decreasing trend as density increased in one of the populations. The relationship of aggression to infant mortality is discussed. In view of the data gathered from the populations it was concluded that aggression did not directly affect infant mortality in either of the populations.