Designing better nestboxes: Double-walled and pale proves coolest under the sun

Publication Name

Pacific Conservation Biology


Context: Fauna nestboxes are used for conservation, research and mitigation against tree hollow/cavity loss. Scant attention has been given to the microclimate inside boxes until recently, with concern that nestboxes may be ineffective or a thermal trap because of high internal temperatures during summer. Aim: Our study used construction design principles to guide modifications to nestboxes to reduce maximum temperatures inside boxes. Methods: Five trials were undertaken, and modifications included addition of thermal mass, creation of a double wall system and painting the box and/or outer wall white. Nestboxes were placed in full sun. Key results: The internal temperature difference from ambient between the worst (unpainted box) and the best box design was around 7°C at 30°C, and 9.5°C at 40°C. Painting boxes white had a marked impact on internal temperatures, but the single modification giving most protection from heat gain was construction of a ventilated double wall. This created a shaded air space around the internal box. Painting the outer layer white further improved insulation, and painting both the box and outer layer gave the best result. Conclusion: Double-walled, pale nestboxes can provide significant protection from solar heat. Implications Adding an air space to insulate a nestbox has considerable advantages over alternatives - it contributes little weight (compare using denser wood/materials); avoids environmental issues associated with insulators such as polystyrene or foil batts; is inexpensive; is easy to retrofit a second layer around existing boxes and it should improve nestbox longevity as the outer layer protects the inner box from weathering.

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