Nest boxes as a recovery tool for hollow‐using mammals following fire

Abstract Tree hollows are a critical habitat resource for a vast array of vertebrate species globally; in Australia, they are used by over 300 species of birds, mammals, and reptiles. The decline of hollow‐bearing trees due to disturbances like shifting fire regimes has prompted the use of nest boxes as a key conservation intervention. However, despite their widespread application, the efficacy of nest boxes in supporting arboreal mammals, especially in post‐fire environments, is not well established. Following the 2019–2020 megafires in Australia, our field experiment evaluated the effectiveness of nest boxes in supporting arboreal mammal recovery. We deployed six nest boxes at each of nine sites (54 in total), including six burnt and three unburnt sites, and compared arboreal mammal activity at these sites with activity at equivalent control sites, which had no nest boxes (six burnt and three unburnt sites). We used baited camera traps to survey arboreal mammal activity 2 months prior to nest box deployment and 24 months post‐deployment. We also assessed nest box occupancy by physically checking the boxes, and with camera traps, over 2 years. Nest box cameras showed that boxes were visited as early as 1 month post‐deployment, but occupancy was low when nest boxes were first physically checked at 9 months post‐deployment (17% in unburnt sites, 0% in burnt sites). At 24 months post‐deployment, mean nest box occupancy was 50% in unburnt sites and 61% in burnt sites. The population surveys using baited camera traps revealed a stronger increase in arboreal mammal activity over time at burnt sites without nest boxes compared to those with nest boxes. Conversely, in unburnt sites, activity was steady over time in control sites but increased at nest box sites. Our findings suggest that while nest boxes provided minimal benefit for arboreal mammals within burnt sites, they may benefit populations in adjacent unburnt areas.