The stimulus-basis of a natural food aversion in Norway rats.

During a 30-min test, hungry adult male Norway rats were permitted to feed on male rodents, freshly sacrificed by CO2 asphyxiation. In Experiment 1, the proportion of subjects feeding on the intact carcass of a dead conspecific decreased as a function of the dead conspecific's age. But the proportion of subjects feeding on the intact carcass of a dead house mouse remained high, regardless of the mouse's age. In Experiment 2, Norway rats were as likely to feed on tissue (heart, liver, and blood) from a conspecific as on tissue from a roof rat. In Experiment 3, lesions of increasing size on the skin of an adult conspecific attenuated and finally eliminated the aversion by Norway rats to feed on the conspecific. Taken together, the present and earlier findings suggest that the tendency by Norway rats to reject a dead adult conspecific as food is mediated, at least in part, by the same species-characteristic odor from the conspecific's inedible coat by which ras identify one another as conspecifics.