Free-operant comparisons of wild and domestic Norway rats.

Wild and domestic rats (Rattus norvegicus) were compared on nondifferential appetitive variable interval responding, discrimination, and discrimination reversal procedures. The effects of strain, sex, deprivation, preexperimental handling, and sessions on response rate were examined. Performances during the 60 days of variable interval training showed prolonged increases over that period for all strain-sex groupings, with domestic subjects responding at higher rates than wild. Males also tended to respond at higher rates than females. During the discrimination procedure wild subjects showed more resistance to extinction than did the domestic subjects, although these differences generally diminished after the 30 days of training. During the discrimination reversal procedure domestic subjects reversed their responding pattern more readily than did the wild subjects, and domestic females reached criterion significantly sooner than domestic males. The effects of deprivation and handling were not significant during the experimental procedures.