Tree Hollows & Bushrock - Homes for Wildlife

Cockatoo peeking out of a tree hollow
What are tree hollows and how do they form?

Tree hollows form in the trunk or branches of live or dead trees, and usually are found in much older trees of typically 100-150 years old. These hollows are a vital resource for native wildlife.

Openings of hollows used by wildlife can be as small as 2 cm to as large as 75 cm. Trees with hollows can occur in paddocks, bushland, backyards and reserves.

Young trees do not generally contain hollows for wildlife as they are healthy and resilient to factors contributing to hollow formation. As trees age over time, they are subjected to natural forces such as wind, heat, fire, lightning, rain, fungi, bacteria, and attack from insects such as termites and beetles. 

Fire can contribute to the creation of hollows in trees. An intense fire or repeated burns can lead to a shortage of hollows for wildlife but can also assist in the process of hollow formation.

Wildlife will also renovate hollows using beaks, teeth or claws.

Eucalypts usually shed or self prune their lower branches as they grow, exposing the point of branch attachment which may eventually develop into a hollow. 

Why are tree hollows so important?
Cockatoo sitting in a tree hollow.
Cockatoo sitting in a tree hollow.

Hollows are an incredibly valuable resource for many native species but take many years to form, so there is an urgent need to protect them.

They are used as a refuge during severe weather events as well as for protection from predators.

They are also an essential roosting and breeding site for several species, including birds, bats, possums, reptiles and frogs. 

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). 

Only old trees have hollows. As they fall and die or are logged or cleared, they can not be replaced without 100 or more years of growth, maturity and decay.

Because they take so long to form, and are such important habitat for many of our native animal species, it is vital that tree hollows are retained wherever possible.

What tree species produce hollows?

Most species of eucalypts and other long-lived trees produce hollows.

In general, gums and boxes tend to produce hollows more readily than stringybarks and ashes.

Many introduced trees such as willows, pines and conifers do not produce suitable hollows for native wildlife.

How can you help to protect tree hollows?

When undertaking developments or landscaping, efforts should be made  protect all trees with hollows including dead standing trees (stags) wherever possible.

An arborist can assist you to ensure these are kept in a safe condition.

Additionally, young trees are needed to eventually develop into mature trees that will form future hollows for animals.

Nest boxes

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:

Nest Box Installation Guide(PDF, 737KB)

Complementing the guide are two templates:

Nest Box Installation - Recording Template
Nest Box Monitoring - Recording Template

Scar from bushrock removal Credit: D Pike.
Scar from bushrock removal Credit: D Pike.

Bushrock 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 bushrock 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.

Bushrock should also not be taken from the bush for landscaping purposes. For more information, watch the below video by the NSW Department of Planning and Environment.

Bushrock belongs in the bush, not in your garden

More information

Learn more about how you can create or conserve habitat for wildlife in your backyard or property: