IZUMI, Tsuyoshi (Dept.Sociol., Primates Research Inst., Kyoto Univ., Inuyama) Social behaviour of the Norway rat (R.norvegicus) in their natural habitat (-especially on their group types) Jap.J.Ecol.23,55-64 (1973) In order to clarify the social characters of the Norway rat in the wild situation, observations were made at several places in Japan. At the first stage, after some observations for the recognition of group members, 10 living dens (Fig.3-10), together with refuge dens (Fig.1) and storage dens (Fig.2) were excavated. Eight kinds of components were distinguished in the composition of two types of living dens consisting of the standard and the complex (Table 1 & 2). At the second stage, 4 additional groups (Group no.11-14) of rats were observed in more detail. The Provisionization was taken for this purpose, and most of the adult rats were discriminated individually (Table 3,Fig.11 & 12). After these observations and excavations, the social character of the Norway rat was considered as follows ; 1) Solitary adult male and female appear to loose antagonism after encounterings for several days (Group no.14). 2) One pair of adult male and female and their offsprings in the early stage occupy a standard living den (Nest no.2 and Group no.11-a). 3) After the offsprings had reached an adolescent stage, the social pattern was changed a little, when the parents still held the position of top male and female respectively. Some son rats joined the upper class and had special social function, but the other sons and daughter rats formed the lower class. They lived in a complex type of living den (Nest no.8,9 & Group no.11-b, 12). 4) A more complexed large group, which had less antagonism and less sociality, but still held some social unity was observed (Group no.13), but some dubious points remained in this group. 5) Throughout the above, in the case food is scarece, rats live as small family groups or solitaries, and when food is sufficient, the offsprings remain in the parent group even after maturation and diverge to two social classes. But the destroyment of the nursery in one of the complex types (Nest no.9) suggest the unusuality of this type. The most stable and fundamental social bond seemed to be of the small family type.
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