SOCIAL AND SPATIAL-ORGANIZATION OF FREE-RANGING SHREWS, SOREX-CORONATUS AND NEOMYS-FODIENS (INSECTIVORA, MAMMALIA)

The social organization of free-ranging Sorex coronatus and Neomys fodiens was studied by measuring the spatial distribution and temporal avoidance or aggregation of individuals, using simultaneous radio-isotope tracking of several shrews. Sorex coronatus was strictly territorial during the non-breeding season, with little overlap between home ranges and low coincident activity between individuals. In the breeding season, females remained strictly territorial, whereas large home range overlap between males and females and also between males was observed. During this season, males kept intensive watch on one female and occasionally visited a second, which in turn was regularly visited by another male. This behaviour suggests a monogamous mating system with a tendency towards polygamy. Neomys fodiens was territorial during the non-breeding season. Each individual defended a portion of a river but a slightly greater home range overlap was observed between rather than within the sexes. During the breeding season, females remained strictly territorial, whereas males tended to wander, indicating an 'overlap promiscuous' mating system. After weaning, juveniles of both species dispersed rapidly and became territorial until the following breeding season. These results were compared with published data on Crocidura russula. During the non-breeding season, there are two types of social organization: A colonial system in C. russula, where coincident rest between individuals allows them to reduce their daily expenditure of energy by social thermoregulation; and a territorial system in S. coronatus and N. fodiens, which may ensure an adequate food supply. During the breeding season for all three species females are strictly territorial perhaps to ensure they have sufficient food for their litters. For the males, three different strategies have been observed and these are also discussed. © 1993 The Association for the Study of Animal Behaviour. All rights reserved.