Tree‐cavity‐dependent wildlife faces future shortages of cavities due to a decline in the abundance of large, old trees in many parts of the world. Nest boxes are proposed as a tool to restore habitat value but evidence of their effectiveness for arboreal mammals remains equivocal. This may arise from a poor understanding of design preferences. We conducted investigations in two landscapes in eastern Australia to determine whether species show a preference for specific designs. We observed a preference by some mammal species for particular designs (33–78% occupied/used), suggesting that design refinement can improve the frequency with which nest boxes are used. Although feral species may out‐compete target species for nest boxes, we did not observe this. We recorded feral honeybees (Apis mellifera) in 6–9% of nest boxes but they did not remain, and many occupied boxes were later used by mammals. The introduced common myna bird (Acridotheres tristis) was prevalent in one landscape, but competition for nest boxes was localized. For nest boxes to be an effective habitat restoration tool, they must be able to be occupied over long periods of time. We investigated this for the squirrel glider (Petaurus norfolcensis), an arboreal marsupial threatened through part of its geographic range. Squirrel gliders occupied and bred within nest boxes (100% used) at two locations continuously over a 10‐year period with minimal nest box maintenance. Individuals occupied boxes for up to 7 years. This confirms that targeted nest box programs can be an effective restoration tool for cavity‐dependent arboreal mammals.

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Bat boxes are commonly used as a conservation tool. Detailed knowledge on the influence of box elements on microclimate is lacking, despite eco-physiological implications for bats. Summer and winter box temperature and relative humidity patterns were studied in narrow multi-chambered plywood and wood-cement boxes in eastern Australia. Box exteriors were black or white and plywood boxes comprised vents. Relative humidity was higher in white boxes than black boxes and box colour, construction material, chamber sequence and vents influenced temperatures. Maximum box temperature differences between designs varied by up to 9.0 • C in summer and 8.5 • C in winter. The black plywood box consistently recorded the warmest temperatures. This design comprised a temperature gradient between chambers and within the front chamber (influenced by vent). During the 32-day summer sampling period, the front chamber rarely recorded temperatures over 40.0 • C (postulated upper thermal tolerance limit of bats), while the third and fourth chamber never reached this threshold. At the study site, the tested black boxes are considered most thermally suitable for bats during average summer conditions. However, during temperature extremes black boxes likely become too hot. Wood-cement, a durable material not previously tested in Australia should be considered as an alternative construction material.

Managing the availability of shelter sites is central to the conservation of vertebrate wildlife dependent on tree hollows (cavities) because hollow abundance has been reduced in many landscapes and trees do not typically acquire hollows until they are at least 100 years old. Artificial hollows (nest boxes) provide one option to offset local shortages in tree hollows. However, knowledge of preferred designs is required for this to be effective. We investigated nest box preference by the eastern pygmy-possum (Cercartetus nanus), a small marsupial recognised as threatened across part of its geographic range in eastern Australia. We installed nest boxes of four different designs in each of 30 plots where tree hollows were scarce. Designs showed no significant difference in thermal profile. We captured 223 adult and subadult pygmy-possums within 78% of the 120 boxes. Breeding females used boxes more frequently than adult males and showed a preference among the designs whereas males did not. Females favoured plywood nest boxes over a PVC design offering a horizontal cavity. Use of the PVC design increased when repositioned to present a vertical cavity. Thus, breeding females are selective of the cavities used to rear young, which may limit local population size.