Path integration by swimming rats

Path integration is a process that enables a moving animal to memorize the location of the starting point of its outward path relative to its current position by continuously processing motion-related information collected en route (route-based information). There has been no evidence, however, that path integration could be used by a swimming animal, even in aquatic or amphibious species. I conducted water maze experiments to test whether rats, Rattus norvegicus, can rely on path integration while swimming, in order to return to a hidden escape platform after circular outward paths ranging from 60 degrees to 300 degrees. Rats proved able to perform the task in a few days. No systematic errors in the distribution of return directions could be observed. In contrast, there was a fairly large random error (about 55 degrees), which, surprisingly, did not depend on the outward path length. Comparison with walking rats could not be made because of the lack of published data. However, results for walking hamsters, Mesocricetus auratus, showed that their random errors are slightly smaller than those made by swimming rats. Such large errors are likely to prevent rats as well as hamsters (and presumably any swimming or walking mammal) from using path integration over long outward paths. (C) 1997 The Association for the Study of Animal Behaviour.