Aggression and timidity: Responses to novelty in feral Norway rats

55 wild rats were reared under various conditions and tested for amount of aggression exhibited toward human handlers, conspecifics, and mice, and for timidity. Additional Ss were amygdalectomized and tested as above. Results were: (a) rearing Ss with albino foster mothers had no effect on performance on any test; (b) rearing Ss with periodic human handling reduced aggression to humans but did not affect other measures; (c) rearing Ss with mice reduced aggression toward mice but did not affect other measures; (d) members of an established colony did not fight among themselves but attacked unfamiliar wild rats; and (e) amygdalectomy reduced aggression and timidity in Ss. Results are discussed in terms of the role of stimulus novelty in eliciting aggression and timidity. (22 ref.)