Augmented hollows and nest boxes for wildlife

Artificial nest boxes and hollows play an important role in providing safe homes for fauna in areas where vegetation is too young to offer natural hollows. This can be important for bushfire recovery and as part of a native revegetation project.

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Nest boxes

Where hollow-bearing trees have been removed, artificial hollows may provide an adequate short-term substitute.

Nest-boxes are only a solution in those areas which have potential to provide suitable habitat for native fauna, for example, with abundant food resources such as flowering eucalypts and wattles.

Boxes should be checked at least twice yearly to ensure that bees have not taken over the boxes. Do not check boxes too regularly as this may discourage fauna from using the box.

Identify your species

Before you start you need to choose which animals you will build boxes for. Wildlife can be very fussy so you need the correct design and dimensions to attract your target species.

How many to build?

Most animals use multiple hollows and regularly change hollows. This helps keep their hollows clean and free of parasites or disease. It also helps them avoid predators such as owls which quickly learn which hollows are in use.

Because they rotate homes, you should provide multiple nest boxes to support each individual animal. If possible, provide at least 4 nest boxes for each species you want to assist.

Selecting materials for a nest box

Strong, warm materials are essential for successful nest boxes and there are no cheap short-cuts. Natural tree hollows provide excellent insulation against the cold/heat and last for a very long time.

Next boxes should be built using a rough timber to ensure that native animals can climb on the box.

Warm and tough materials are critical for your nest box to be effective. Pine, interior ply and any materials under 15 mm thickness are not suitable. These materials won’t last more than 5 years outside and don’t provide enough thermal insulation for wildlife.

Choosing the best wood will give your box good insulation or ‘thermal mass’.

Common materials in decreasing suitability include:

Hardwood is best, preferably greater than 15 mm thick.
Marine ply will last a few years but needs to be at least 17 mm thick.
Exterior ply is the least durable and warm and needs to be at least 17 mm thick.

Nest box design

A 4 cm entrance hole should be placed on the face of the next box. The small size of the entry hole aims to restrict other fauna from using the box.
In the base of the box a number of 5mm drainage holes should be drilled to prevent the box from flooding.
A lid on the top will mean the box can be checked easily.
To make the box more comfortable wood shavings can be placed in the bottom.

Installing your nest box

Choosing a tree and location

Make sure you select a location away from disturbance and street lights which may spook wildlife.
Facing generally north and using a variety of orientations with your boxes can ensure wildlife have a good selection of sites.
Consider placing nest boxes on the leeward side of a tree, away from the prevailing weather.
Boxes should be placed between 2 and 4m above the ground with the entrance close to the tree.

Installing your box

The easiest way to install your box is with an extension ladder. Make sure you are safe at all times and the ladder is secure as installing the box can be tricky.
Remember that you will want to access your box later to clean it or to check it so make sure it is reasonably accessible.
Spring-wire attachments are best but require regular inspection and adjustment to avoid strangling the tree or damaging the nest box
Where regular adjustment is not guaranteed boxes can be drilled directly into trees using two coach screws spaced vertically.
Drill bits and screws should be sterilised to avoid harmful fungi infecting the tree. You can coat your screws with organic oil (for example tung or linseed oil) to sterilise them before use.
Holes and screws must be deep to ensure a strong connection (at least 80 mm).
Make sure your screws are long enough to get through the tree bark and into the sapwood.

Augmented hollows

An augmented hollow is the creation of a hollow within an existing tree. This provides an environment that is much more suitable for animal habitation as compared to artificial nesting boxes that attach to the outside of the tree.

Pruning or boring to create a hollow by cutting a nest box into a tree requires a high level of skill.

Arboriculture work that requires the use of a chainsaw should be conducted by professionals.

A hollow tree branch inserted into a tree trunk

Success stories

Following the devastation of the Dunns' Road bushfire in the Riverina region, many held grave concerns for local populations of greater gliders. Funding from the Australian government supported a monitoring and recovery program which included the installation of augmented hollows and nest boxes.