PREDATION AND HABITAT SHIFT IN THE HOUSE MOUSE, MUS-DOMESTICUS

This study investigates the responses of house mice (Mus domesticus) to two species of introduced mammalian predators in Western Australia, the red fox (Vulpes vulpes) and cat (Felis catus), and to an endemic carnivorous marsupial, the western quoll (Dasyurus geoffroii). In four study areas containing no mammalian predators, mice showed little discrimination between traps bearing fecal odors of the predators and traps bearing conspecific odors or no odor. Mice in these areas also used sites of different vegetation density roughly in proportion to their abundance, irrespective of the intensity of lunar illumination or whether densities of predator feces were high or low. These results suggest that predator-naive mice do not respond to predator odors or to different levels of predation risk. In contrast, mice in 12 other study areas containing one to three species of mammalian predators avoided traps with predator odors, and generally selected relatively dense vegetation. They also used sites of greater vegetation density on moonlit compared to dark nights, and in two study areas where the density of cat feces had been experimentally increased. These results indicate that mice in areas exposed to mammalian predators distinguish predator odors and use denser vegetation when the perceived risk of predation is increased. In further experiments, I introduced predator-naive and predator-experienced mice to study areas containing cats and foxes. Survival rates of experienced mice a month after release were 2 1/2 times higher than those of their naive counterparts, and hence support the hypothesis that a habitat shift to dense vegetation is an effective anti-predator response.