Service update: Phase two of our eServices platform to enhance and digitise our services to the community will launch on Monday, 15 December 2025. Customers will be able to easily lodge and pay online for 8 more online applications, streamlining the application process. If you have any questions, please call us on (02) 4868 0888.
Tree hollows form in the trunk or branches of live or dead trees and usually are found in much older trees.
Several processes can occur—often in tandem—to create a hollow inside a tree. Some key factors include:
Tree hollows can take decades to centuries to develop, depending on the tree species and environmental conditions. In many cases, it takes over 200 years for a tree to form a hollow large enough for wildlife such as possums and parrots. The loss of old-growth trees means there is a critical shortage of hollows in many landscapes.
For most native vertebrate species in Australia, tree hollows are used for three primary purposes:
Different species rely on different types of hollows, making the presence of varied hollow types essential for biodiversity. Tree hollows come in a variety of forms:
In Australia, Eucalyptus species are among the most important trees for hollow formation.
In contrast, introduced species like willows, pines, and conifers rarely produce ideal hollows for use by our larger native vertebrate species.
At least 304 vertebrate species in Australia depend on tree hollows for shelter and nesting. This includes:
Examples of animals that use hollows in our shire include Glossy Black Cockatoos, Powerful Owls, Sugar Gliders, Squirrel Gliders, Kookaburras and the Eastern False Pipistrelle (microbat).
A diversity of hollows in different tree species, sizes, and ages is crucial to support the widest range of wildlife - with some studies suggesting that at least 30 hollows per hectare are needed to support native wildlife.
The loss of hollow-bearing trees in agricultural and urban landscapes has severely impacted biodiversity, making their conservation a priority.
In areas where natural tree hollows are scarce, nest boxes may be used as artificial hollows for many hollow-dependent fauna species. It is important to recognise that although nest boxes may increase habitat for many fauna species, they should not be considered a replacement for natural tree hollows.
There are also several planning, installation and monitoring considerations that come with determining whether a nest box is a suitable option for assisting native wildlife.
To assist you or your group with deciding whether a nest box is suitable, please review our nest box guide:
Complementing the guide are two templates:
Alternative options to nest boxes, include hollow hogs and cut-in hollows.
Bush rock is loose, fragile rock found on rocky or soil surfaces. Like hollows, it can take a long period of time to form and is critical habitat for many species.
When available, many animals use the habitat created by bush rock as shelter to avoid extreme weather and bushfires, protection from predators and as nest sites for reptiles.
Plants such as mosses, lichens and liverworts also thrive in areas with bush rock.
In order to retain this valuable habitat, it is important to minimise disturbance to rocks while you are out bush walking or mountain biking.
Bush rock should not be taken from the bush for landscaping purposes.