Helping wildlife beat the heat: Testing strategies to improve the thermal performance of nest boxes

Nest boxes are often deployed in an attempt to offset the loss of natural tree hollows following landscape disturbance (e.g., land clearing, logging and wildfire). However, nest boxes can experience more variable and extreme microclimates than natural hollows, which could harm animals that use them. In this study, we tested the thermal performance of candidate nest box designs prior to their deployment for greater gliders (Petauroides volans) in forests impacted by the 2019–2020 bushfires. The tests were conducted under controlled laboratory conditions to investigate the thermal response of different designs to radiant heat and changes in ambient temperature. We examined how paint type (i.e., no paint, white exterior paint, and reflective white paint), insulation thickness (0 mm, 20 mm, and 40 mm Foilboard), and insulation amount (i.e., number of sides insulated) influenced the internal temperature profiles of these nest boxes. We found that nest boxes with the reflective white paint had the lowest temperatures on the inside wall closest to the radiant heat source, but internal nest box air temperature did not differ among paint treatments. Similarly, the internal wall closest to the radiant heat source was cooler in nest boxes with thicker compared to thinner insulation, but there was no difference in internal air temperature between the two thicknesses. Both 20 mm and 40 mm Foilboard insulation resulted in significantly cooler air temperatures and internal wood panel temperatures compared to nest boxes without insulation. Fully insulated nest boxes and those with three of the four sides insulated exhibited less temperature variability and remained cooler than the less-insulated nest boxes. Temperatures inside nest boxes with more than one side insulated took longer to increase and decrease in a convective heat chamber, but importantly, never reached the heat extremes (> 40°C) of less insulated nest boxes. Fully insulated nest boxes also maintained heat longer than any other nest box type in a cold room. Understanding how different construction materials influence nest box temperature profiles and identifying designs that minimise thermoregulatory costs for animals is important for the safe implementation of nest box programs.