Central injections of serotonin (5-HT) in food-deprived/refed pigeons evoke a sequence of hypophagic, hyperdipsic and sleep-like responses that resemble the postprandial behavioral sequence. Fasting-refeeding procedures affect sleep and drinking behaviors "per se". Here, we describe the behavioral profile and long-term food/water intake following intracerebroventricular (ICV) injections of 5-HT (50, 150, 300 nmol/2 µl) in free-feeding/drinking pigeons. The patterns of Fos activity (Fos+) in serotonergic (immunoreactive to tryptophan hydroxylase, TPH+) neurons after these treatments were also examined. 5-HT ICV injections evoked vehement drinking within 15 min, followed by an intense sleep. These effects did not extend beyond the first hour after treatment. 5-HT failed to affect feeding behavior consistently. The density of double-stained (Fos+/TPH+) cells was examined in 6 brainstem areas of pigeons treated with 5-HT (5-HTW) or vehicle. Another group received 5-HT and remained without access to water during 2h after treatment (5-HTØ). In the pontine raphe, Fos+ density correlated positively to sleep, and increased in both the 5-HTW and 5-HTØ animals. In the n. linearis caudalis, Fos+ and Fos+/TPH+ labeling was negatively correlated to sleep and was reduced in 5-HTØ animals. In the A8 region, Fos+/TPH+ labeling was reduced in 5-HTW and 5-HTØ animals, was positively correlated to food intake and negatively correlated to sleep. These data indicate that hyperdipsic and hypnogenic effects of ICV 5-HT in pigeons may result from the inhibition of a tonic activity of serotonergic neurons, which is possibly relevant to the control of postprandial behaviors, and that these relationships are shared functional traits of the serotonergic circuits in amniotes.