Looking for the possum’s bum is a daily ritual for Museum commuters walking from Town Hall station. By noting whether the hollow in the Hyde Park melaleuca is occupied or unoccupied, we have been quietly monitoring occupancy rates of inner-city tree hollows. But until Hollows as Homes began, there wasn’t an easy place to record these observations. Now that I can register hollows on my phone and then log updates on the animals using them, I find myself paying a lot more attention to holes in trees, and hopefully lots of other people will too.

Hollows as homes project
Competition for tree hollows can be intense: Common Brushtail Possum (Trichosurus vulpecula) and Sulphur-crested Cockatoo (Cacatua galerita) at nest hollow. Image: Richard Major
© Australian Museum

In urban and agricultural areas throughout Australia, hollow-bearing trees are in decline. In New South Wales, terrestrial vertebrate species that are reliant on tree hollows for shelter and nesting include at least 46 mammals, 81 birds, 31 reptiles and 16 frogs. Of these, 40 species are listed as threatened with extinction in New South Wales. This is why the ‘loss of hollow-bearing trees’ has been listed as a key threatening process.

Hollows as homes project
Rainbow Lorikeets (Trichoglossus haematodus) at their nest hollow. Image: Richard Major
© Australian Museum

With the help of the community Hollows as Homes aims to measure the availability of tree hollows and their use by wildlife. Participants in the program are reporting hollows in backyards, streets, parks, paddocks and the bush by visiting www.hollowsashomes.com. On-line training is provided on how to take measurements of the hollow-bearing tree and periodically report the wildlife using this important resource.

Hollows as Homes Project
Even London Plane Trees Platanus × acerifolia are used for nesting cockatoos (inset). Note the chips of decaying wood that have been excavated by the nesting birds. Image: Richard Major
© Australian Museum

Although the project was only launched this year, there are now plenty of records of the hollows used by lorikeets, wood-duck, powerful owls, king parrots, brushtail possums and sugar gliders – to name a few. The website enables individuals and land-managers to view the data both spatially and numerically, and in the long term we hope that the data will guide decisions about hollow retention and provision.

Unfortunately many hollow-bearing trees are removed because of concerns about public safety. In some cases the losses are supplemented by the installation of artificial nest boxes and the relatively-new technique of cut-in tree hollows. Hollows as Homes provides the infrastructure to monitor these initiatives to determine their benefits for biodiversity conservation. However, to be successful, the project needs big data, so if you have a nest box or next time you see a hollow, please google Hollows as Homes.

Dr Richard Major
Principal Research Scientist

More Information

The Hollows as Homes program is coordinated by the Royal Botanic Garden Sydney, University of Sydney and Australian Museum, and is supported by the Sydney Coastal Councils Group through funding from the Australian Government.