1. The seasonal reproductive cycles of male and female Pt. poliocephalus, Pt. gouldi and Pt. scapulatus are described and the age, length of forearm, and body weight at maturity of Pt. poliocephalus and Pt. scapulatus are determined. The variation in the conception times of Pt. poliocephalus and Pt. scapulatus is correlated with differences in the geographical range and food supply of the two species.
2. The seasonal movements of flying foxes are correlated with the seasonal variation of the food supply. These movements are into large communal camps in early summer when blossom is plentiful and then disperal from these camps in late summer when blossom is scarce, however, when blossom is abnormally abundant in winter, the adult population "winter" in the winter camps of the young.
3. The behaviour and social organisation of three species of Pteropus are described and compared. In Pt. poliocephalus and Pt. gouldi. summer camps form in September, the young are born in October when the sexes are segregated, selection of a mate occurs in December-January, territories are established and defended during February, March and April, and after conception in late March the sexes segregate within the camp and then disperse from the camp in mid April. Winter camps containing mainly juveniles are occupied from April to September. In Pt. scapulatus the territories are defended in November and after conception in late November the sexes segregate within the camp. The young are born in April when the species is dispersed through its range.
4. A number of vocal communications of Pt. poliocephalus have been analysed by a sound spectrograph. These are described physically and correlated with behavioural observations.
5. The relations of body temperature, oxygen consumption, and heart rate to ambient temperature were studied in Pteropus poliocephalus, Pt. scapulatus, and Syconycteris australis. The two species of Pteropus maintain body temperature in the usual mammalian range in ambient temperatures extending from 5° to 40°C. At low ambient temperatures they can surround themselves with a layer of air as much as 10° above ambient by enclosing their bodies in their wings. At ambient temperatures above the usual level of body temperature a variety of mechanisms are used for heat dissipation - panting, wing-flapping, salivation, and licking of the wings and chest. Both species tolerate some hyperthermia without apparent distress, but Pt. scapulatus allows its body temperature to rise more than does Pt. poliocephalus before activating its mechanism for heat dissipation.
Syconycteris australis is unable to maintain its body temperature when ambient temperature approaches 0°, but body temperature is independent of ambient temperature between 10° and 30°. At ambient temperatures between 30° and 35° hyperthermia develops.