1. A choice between a high-energy, wheat-based, low protein mixture and a lower-energy, soya-based, high protein mixture was offered to growing Japanese quail at ambient temperatures of 20°, 25°, 30° and 35°C.

2. The quail were kept in open-circuit respiration calorimeters, so that diet selection could be related to energy requirement.

3. Increasing ambient temperature had no significant effect on food intake by weight, but the proportion of the high energy choice decreased and, conversely, the proportion of the lower-energy but higher-protein choice increased.

4. Energy intake was therefore negatively correlated with ambient temperature, but protein intake per unit of energy intake increased, allowing the birds to gain weight at about the same rate at all temperatures.

5. Heat production decreased as ambient temperature increased. Respiratory quotient decreased with increasing temperature, which indicates a reduced utilisation of carbohydrate as an energy source.

6. Water intake increased with temperature but there were no overt signs of heat stress and there was no significant change in body temperature.

7. Japanese quail selected a dietary mixture which maintained similar growth rates over a wide range of ambient temperature, by sustaining protein intake but altering energy intake in line with thermoregulatory energy demands.