Exploratory behaviour of colonizing rats in novel environments

The immediate movement and behaviour of individuals arriving in novel environments influence long-term survival and population establishment. Studies have previously investigated exploratory behaviour in novel laboratory environments, but never during colonization of natural systems. Experimentally releasing and monitoring animals would allow testing of laboratory and computer-simulation hypotheses. We sequentially released and tracked three adult male brown rats, Rattus norvegicus, on a rat-free island, monitoring their movements hourly for 3 weeks to test laboratory and simulation-generated hypotheses of how animals explore and move in novel environments. We found that (1) individual movements are apparently random; (2) range size increases most rapidly in the first week after arrival; (3) range size is larger than for individuals at high density; (4) movement is mediated by central place foraging behaviour. These findings contradict laboratory hypotheses of nonrandom exploration but support simulation search strategy hypotheses. Random movement and increased ranges at low density have implications for understanding animal colonization dynamics and intercepting invasive species arriving at new locations.