Circadian feeding and locomotor rhythms in pigeons and house sparrows

Feeding and locomotor activities were measured simultaneously in homing pigeons (Columba livia) and house sparrows (Passer domesticus). Feeding, as well as locomotor activity, was found to be regulated by a circadian clock in both of these species. Implantation of melatonin-filled capsules or exposure to constant light abolished feeding and locomotor rhythms in both species. Removal of the pineal gland from pigeons did not abolish either rhythm, whereas pinealectomy abolished both feeding and locomotor rhythms in house sparrows. Although feeding rhythms were generally more robust than locomotor rhythms in both of these species, different feeding and locomotor free-running periods were not observed within any individual pigeon or house sparrow. These results are consistent with the hypothesis that each of these species has a single pacemaker that regulates the timing of feeding and locomotor activity, but they do not rule out the possibility that separate clocks regulate these behaviors.