Responses of Wild Norway Rats (Rattus norvegicus) to Predator Odors

Abstract

If rats could be shown to avoid the odors of predators, then conservation managers could manipulate this behavior to exclude rats from important conservation sites. We evaluated the ability of six predator odors to elicit avoidance responses by wild-caught Norway rats (Rattus norvegicus) from two New Zealand populations (Kapiti Island and North Island). Kapiti Island is free of mammalian predators, while the North Island has established populations of felids, canids, and mustelids. Three of the predator odors were real and three were synthesized volatile ingredients of real animal feces or urine. We compared the rats' responses to predator odors with their responses to three natural herbivore odors. We used a Y maze, and rats were offered the choice of an odor in one arm of the maze and distilled water in the other arm. Each choice arm was ducted at the entrance to remove air and the odor. We recorded: (1) the time until the rat left the first arm of the maze, (2) the time until the rat visited each arm, (3) the number of visits to each arm, (4) the amount of time spent in each arm, and (5) a total activity score for each rat. Kapiti rats showed an aversion to five of the six predator odors, despite never having encountered them before. Kapiti rats visited herbivore odors more often than carnivore odors and were less active in the presence of carnivore odors than they were when tested with herbivore odors. In addition, Kapiti rats approached some herbivore odors more quickly than they approached carnivore odors. North Island rats appeared to avoid cat urine, but despite being predator experienced, did not show a consistent aversion to the carnivore odors we tested. Both samples of rats, but particularly the North Island group, showed high individual variation. We conclude that predator odors are unlikely to be an effective management tool for all populations of this species of rat because of this high individual variability and the likelihood that each island population will differ in its responses to a given odor.