The use of artificial hollows by tree hollow-using Australian marsupials: what have we learnt in the past 20 years?

Artificial hollows (predominantly nest boxes) have been used over many decades to study Australian marsupials that require tree hollows for shelter and for breeding. The literature documenting such studies was last reviewed 20 years ago. The present study reviews the studies published in the interim with an aim to (1) synthesise this new literature, (2) describe and evaluate the most frequently studied topics, and (3) evaluate the progress that has been made towards using artificial hollows to manage and conserve tree hollow-using marsupials. I documented 75 studies published between 2006 and 2025, of which 87% had a research focus rather than a management focus. Surprisingly, 58 of the 75 studies were published in the past 10 years. This period saw the introduction in Australia of chainsaw-carved hollows and drilled hollows. A key intention of 14 studies was to use artificial hollows as research tools, enabling access to difficult to capture or observe species, as well as to gain insight into their micro- and macro-habitat preferences. Twenty studies investigated the temperature profiles within artificial hollows, contrasting across types as well as with natural hollows. Consistent findings include that temperatures within nest boxes closely track ambient temperature, including its extremes, whereas those in chainsaw hollows in live trees were buffered and mimic those within natural hollows in live tree trunks. However, chainsaw hollows and natural hollows in dead trees showed poor buffering of ambient temperature. A study that contrasted squirrel gliders (Petaurus norfolcensis) using nest boxes and tree hollows with those using only tree hollows found higher survival among those individuals using nest boxes, suggesting hollow quality has various attributes in addition to the thermal environment. The maintenance of artificial hollows has been advanced previously as a serious concern if they are to be used in a conservation context. Recent studies show all types of artificial hollow require periodic maintenance. Studies of nest boxes over 6–30 years suggest that minor intervention associated with animal monitoring is sufficient. Monitoring of chainsaw hollows over 2–7 years has shown that the entrances to some hollows may become occluded and require periodic intervention. It is hypothesised that artificial hollows will be used more frequently where natural hollows are scarce. This has not been investigated in an experimental context; however, across 11 studies in which relative hollow density could be scored as high or low, higher use of artificial hollows was recorded where density of natural hollows was low. This emphasises the need to evaluate natural hollow deficiencies before embarking on projects that install artificial hollows to achieve conservation outcomes. The only studies in the review period where artificial hollows were installed to provide population support were in the context of animal translocations. Further studies using artificial hollows to achieve population support are required to progress it as a conservation action for hollow-dependent marsupials.