FLIGHT-INDUCED INCREASE IN CIRCULATING LEVELS OF MELATONIN IN THE HOMING PIGEON

1. Homing pigeons, receiving regular flight-training for participation in racing competitions, were flown from their usual release site, 48 km away from ''home''. 2. On their return ''home'' within 60-80 min, b lood samples for the measurement of melatonin were taken within 1-3 mi n of arrival. 3. Post-flight circulating levels of melatonin were foun d to be about 82% higher than those of the resting control pigeons wit hout any change in plasma osmolality. 4. This daytime increase in circ ulating levels of melatonin suggests that melatonin, by virtue of its known hyperthermia effect of facilitating peripheral heat dissipation, could prevent excessive flight-induced hyperthermia. 5. It is also su ggested that the flight-induced increase in plasma levels of melatonin is consistent with the known analgesic and metabolic effects of the h ormone.