Feeding patterns and operant responding by wild and domesticated rats in self-maintenance conditions

The feeding activity of domesticated and wild rats was studied. The rats obtained all their food by lever pressing in two-lever operant chambers. Concurrent variable interval (VI) and concurrent variable ratio (VR) schedules operated continuously for successive 4-day periods. Feeding occurred as regular, discrete meals, mostly during the night. The schedules did not affect the number or size of meals or the total amount eaten. The interval schedules significantly extended the duration of meals and reduced intermeal intervals. Lever pressing was characterised on concurrent VI schedules by low response rates and frequent alternation and that on concurrent VR schedules by higher response rates confined to one lever. The wild rats ate significantly more than the domesticated rats by increasing the number but not the size of meals, primarily during the night. Feeding behaviour and operant responding are discussed in relation to the effects of domestication and economy of effort in food-seeking. The inhibition caused by handling and food deprivation, which impairs the performance of wild rodents in short sessions is avoided by providing self-maintenance conditions.