Young, relatively undeveloped sugar gliders Petaurus breviceps have been observed to be left alone in the nest while the mother forages and may be subject to considerable thermal or energetic stress. As no information is available on the development of thermoregulation in this species, which begins reproduction in winter, we measured resting metabolic rate (RMR), body temperature (Tb) and thermal conductance over a range of ambient temperatures (Ta) in 10 sugar gliders from c. 55 days of age until they had grown to adult size. Sugar gliders were unable to maintain a stable Tb over a Ta range of 30–15 °C until the age of 95–100 days, although they raised RMR somewhat as Ta decreased. Further growth resulted in a steady decrease in mass-specific RMR, an increase in Tb and a substantial decrease in thermal conductance. Our study shows that young gliders below the age of 100 days rely largely on heat produced by adults to maintain a high Tb, but are well able to cope with regular falls in Tb of > 10 °C and a concomitant decrease of RMR. This thermal tolerance and reduction in energy expenditure should allow the mother to forage and replenish her own body fuels while her offspring are left alone in the nest.

The sugar glider Petaurus breviceps is generally considered to be a polygynous, group-nesting species. However, recent captive studies have indicated that dominance hierarchies and shared codominance amongst males formed when males were housed in multiple-male, multiple-female cages with male-biased sex ratios. This study uses data from sugar glider groups in natural populations to assess the probability of male dominance hierarchies and the opportunity for codominant father–son coalitions. Nesting groups of sugar gliders were found to have female-biased sex ratios ranging from 1:1.5 to 1:2.7 males:females. The dispersing sex was male – there were four records of recruitment into the natal group, all of which were female. Only one example was found of a long-term adult male association between a father and putative son, which did not occur in the natal group of the son. The evidence suggests that though father–son associations may occur, the opportunities for male dominance hierarchies or male coalitions are rare in sugar glider nesting groups in the natural environment.