Concurrent drinking by pigeons on fixed-interval reinforcement schedules.

Three experienced pigeons were exposed to at least ten consecutive 100-min sessions on each of three food-reinforced fixed-interval (FI) schedules: FI 50-sec, FI 100-sec and FI 200-sec. Water was freely available. Drinking was largely confined to the first third of each fixed interval, and the mean sessional water intake was directly related to the food-reinforcement rate for each animal. The animals drank very quickly, i.e., 3--4 ml/sec, but the drinking bouts were brief, i.e., 0.8--1.4 sec, and infrequent, i.e., 2--5/hr. The parameters describing concurrent drinking in the pigeon are strikingly different from those describing rats' drinking under similar reinforcement schedules, which may contribute to the difficulty in demonstrating schedule-induced polydipsia in the pigeon.