Choice of monitoring method can influence estimates of usage of artificial hollows by vertebrate fauna

Abstract

The loss of hollow-bearing trees is a key threat for many hollow-dependent taxa. Nesting boxes have been widely used to offset tree hollow loss, but they have high rates of attrition, and, often, low rates of usage by target species. To counter these problems, chainsaw carved hollows (artificial cavities cut into trees) have become a popular alternative, yet little research has been published on their effectiveness. We examined the usage of 150 chainsaw carved hollows by cavity-dependent fauna in the central west of New South Wales using observations from traditional inspection methods and remote cameras. Between October 2017 and April 2019, we detected 21 species of vertebrates (two reptile, one amphibian, 10 bird, and eight mammal species) inside chainsaw carved hollows, but the number of species detected was dependent on the chosen monitoring method. We detected six species inside hollows during physical inspections, whereas remote cameras detected 21 species entering hollows. Cameras detected eight species using hollows as breeding sites, whereas physical inspections detected just four species. Cameras detected two threatened mammals (squirrel glider (Petaurus norfolcensis) and greater glider (Petauroides volans)) raising young inside hollows, yet we failed to detect these species during physical inspections. For birds, the two methods yielded equivalent results for detection of breeding events. Overall, our study showed that few cavity-dependent species used chainsaw carved hollows as breeding sites. This highlights how artificial hollows are not a substitute for retaining naturally occurring hollows in large trees and revegetation programs.

Home is where the hollow is: Revealing vertebrate tree hollow user biodiversity with eDNA metabarcoding

“…While physical inspection only provides data for a single point in time, camera traps provide useful insights into ongoing hollow use and the functional role of hollows (Cotsell & Vernes, 2016; Gregory et al, 2014). They also record more species than do physical inspection of hollows (Honey et al, 2021). However, their use in the monitoring of tree hollows has some limitations.…”

Field methods to identify Palm Cockatoo nest hollows

“…Most observations of rare, flying bird species appear to be opportunistic (O'Brien & Kinnaird 2008). Although time-lapse cameras installed in trees to monitor natural (Honey et al 2021) or chainsaw hollows (Griffiths et al 2020) is not novel, the method of installing eye-level camera traps angled upward to detect occupancy of tree hollows is, to our knowledge, a new approach that reduces the cost of installation/maintenance immensely. Traditional motion-sensor detection settings are not suitable for this type of monitoring at distance because of canopy movement in a wide-angle frame.…”

Thermal Profiles of Chainsaw Hollows and Natural Hollows during Extreme Heat Events

“…We worked on a revegetation and hollow creation project led by the Central Tablelands Local Land Services and the Environment & Waterways Alliance in which artificial hollows were created in standing trees to provide habitats for hollow-dependent wildlife, including the threatened superb parrot Polytelis swainsonii . Hollows were created in trees at 11 sites spread across the Bathurst, Blayney, Cabonne, Cowra, and Orange Local Government Areas in the central west of NSW, a region that is dominated by dryland agriculture and plantations [ 24 ]. Native vegetation in the region comprises grassy woodlands, dry sclerophyll forest, and floodplain transition woodlands [ 29 ].…”

“…Native vegetation in the region comprises grassy woodlands, dry sclerophyll forest, and floodplain transition woodlands [ 29 ]. A total of 187 artificial hollows were installed by qualified arborists between 2017 and 2018 in standing dead trees and live trees in which the ratio of solid wall thickness (t) over trunk radius was >0.3 [ 24 ]. This criterion was used because it provides a reasonable estimate of the likelihood of tree failure, specifically reducing the structural integrity of the tree leading to collapse [ 30 , 31 ].…”

“…While several studies have shown that a diversity of fauna will use CHs [ 22 , 23 , 24 , 25 ], less is known about their thermal properties. Several recent studies carried out in southern Australia found that temperatures inside CHs and natural hollows in live trees were very similar, with both structures providing temperatures that were warmer than ambient at night, and cooler than ambient during the day [ 15 , 26 ].…”