A system for automatic recording of social behavior in a free-living wild house mouse population

Our research focuses on mechanisms that promote and stabilize social behavior, fitness consequences of cooperation, and how interactions with conspecifics structure groups and populations. To this end, we studied wild house mice (Mus musculus domesticus) in the laboratory, in semi-natural enclosures and in the field. In 2002, we initiated a project on a free-living population of house mice in a barn near Zurich, Switzerland, where mice were equipped with RFID transponders and were provided with 40 nest boxes for resting and breeding. The population typically comprised between 250 and 400 mice. Methods: To analyze social group membership, social interactions and social preferences of the mice in our study population over their lifespan, we installed a continuous transponder reading system (AniLoc, FBI Science GmbH, Germany). Mice accessed nest boxes through tunnels equipped with two antennas each. When a mouse implanted with an RFID transponder passed the electromagnetic field of an antenna, its identity was transmitted and registered in real time with AniLoc. Additionally, body weights of mice were automatically registered at eight drinking facilities (Intelliscale, FBI Science GmbH, Germany). Here, a mouse sits on a freely movable platform that connects to a scale registering body weight when drinking, and an antenna around the head of the water bottle registers the drinking individual’s RFID transponder. Results: The system enabled continuous remote monitoring of the behavior of a free-living, open population of house mice, when using nest boxes and when drinking. Since such safe places are an important resource for survival and reproduction, time of day, duration and frequency of meetings with conspecifics reveal information about the function of their interactions. Trigger efficiency of antennas was 98.2 %. Mice entered and left the nest boxes with an average speed of 0.03 m/s, which is within the antennas’ detection capacity (detection speed of 1 m/s or 3.6 km/h). The antenna devices documented not only social structuring of our study population but also spatial genetic structuring. The observation that mice lived in rather closed social groups and tended to share nest boxes with relatives highlights the importance of kin selection for the evolution and maintenance of social behavior. Conclusions: We suggest that such automatic recording of activity, spatial distribution and social interactions is helpful not only in field studies, for a variety of species, but also in captivity or laboratory studies, to answer basic questions in behavioral ecology, population ecology, population genetics, conservation biology, disease ecology, or animal welfare