Occupancy of chainsaw-carved hollows by an Australian arboreal mammal is influenced by cavity attributes and surrounding habitat

Abstract

The creation of mechanically carved tree cavities to provide supplementary shelter for hollow-dependent wildlife is increasingly popular in conservation management programs. However, there is limited empirical evidence quantifying how the features of their design and broader placement within the landscape influence use by target fauna. In this study, we took a multi-scale approach to investigating the use of chainsaw hollows (CHs) by a target native arboreal marsupial, Krefft’s Glider Petaurus notatus. We hypothesized that Krefft’s Gliders would respond to attributes of: (1) the CH itself; (2) the tree into which it was installed; and (3) the habitat within the reserve in which it was located. We monitored occupancy (over 2.7 years, using a pole camera) of 48 CHs installed in live Eucalyptus trees across multiple reserves in Melbourne, Australia, plus visitation (over ∼3 months, using camera traps) to 40 of the CHs. Mixed models were used to relate the occupancy of CHs by Krefft’s Gliders to field-collected data on various attributes of CHs at all three scales. From a total of 35,219 visitations across the 40 CHs, we recorded 13 native hollow-dependent species (five mammals, eight birds) visiting CHs. During 14 pole-camera inspections, Krefft’s Glider occupied 60% of the 48 CHs at least once, with 4% used as maternal dens during breeding. Four exotic species were also recorded visiting and/or occupying CHs. Orientation and volume both significantly affected occupancy: Krefft’s Gliders were more likely to occupy larger CHs, and those facing north and west (possibly related to microclimate). Tree-scale attributes did not affect occupancy, but Krefft’s Gliders were more likely to occupy CHs further from reserve edges, and where local density of Black Wattles (Acacia mearnsii: an important food resource) and low vegetation cover (100–200 cm above ground) was increased. Our findings show that CHs can provide supplementary shelters for Krefft’s Gliders when natural hollows are limited. Practitioners should consider both the physical characteristics of the cavity (e.g. volume) and the surrounding habitat (e.g. availability of foraging resources) to enhance the use of CHs by target species. The ongoing availability of CHs to target species will also be influenced by their use by exotic species, and potential for closure as woundwood grows. In an Australian context, a lack of knowledge about the specific features of natural hollows to which hollow-dependent fauna respond, means it is critical for policy and management to prioritize the retention of mature hollow-bearing trees.