Significant increase in the circulating levels of glucose, lactate, adrenaline (A) and noradrenaline (NA) was observed in homing pigeons after a flight of 48 km, lasting 60-80 min. There was, however, no change in plasma corticosterone concentrations. The increase in lactate has been attributed mainly to the activity of the white glycolytic fibres in the flight muscles. The increase in A and NA indicated increased sympathetic activity. It is suggested that the flight-induced increase in A stimulated the release of glucagon which could account for the increase in plasma glucose. The lack of any increase in plasma corticosterone implied that the birds were not under any serious stress during the flight and that these results represent the normal changes that may be expected in pigeons during a free flight of the specified distance and duration.

Significant increases in circulating levels of free fatty acids (FFA) and growth hormone (GH), were observed in homing pigeons after a flight of 48 km, lasting 60-80 min. No significant change in plasma levels of thyroxine (T4) and triiodothyronine (T3) was observed. Nor was there any change in T3/T4 ratio. The increase in plasma FFA is attributed to the increased release into circulation of at least one adipokinetic hormone, GH. It may be concluded that in free sustained homing flight under normal weather conditions and within the specific distance and duration, metabolic fuel and hormonal homeostasis is maintained.

Concentrations of plasma noradrenaline, adrenaline, corticosterone, thyroxine (T4), triiodothyronine (T3) and prolactin were measured in pigeons at 22 degrees C after intravenous injection of propranolol (1 mg/kg). An increase in catecholamines occurred in 5 or 15 min. T4, T3 and prolactin increased within 30 and 60 min after injection, however, after correction for the differences in plasma protein content, only the concentration of prolactin was significantly above the control values. It is concluded that the impairment of heat production produced by propranolol in birds is not primarily induced by inhibition of the secretion or release of these hormones.