Across Australia, habitat loss including the removal of old, hollow-bearing trees means that animals; birds, bats, possums, microbats and even some native mammals are struggling to find a safe place to nest and shelter.

Installing a nest box in your backyard or property is one of the easiest ways to give our native wildlife a helping hand. A well placed nest box can become a much needed home but only if it’s the right size for the animal you want to attract – because not all animals will use the same type of home.

1. Why Size Matters

A nest box that suits a rainbow lorikeet won’t work for a sugar glider, and a boobook owl certainly isn’t going to squeeze into a rosella-sized hollow! The size of your nest box will determine which species are likely to move in. Different animals have different requirements for:

• Entrance hole size
• Internal volume dimensions
• Depth of the box
• Landing space / Entrance layout

If your box is too small, a bird or bat may not be able to fit comfortably, and if it’s too big, it may feel unsafe or attract predators. Choosing the right size gives your local wildlife the best chance to thrive.

The size of the box and the entrance hole are the two main things that determine which species will use it. Too small, and they can’t get in. Too big, and the animal may feel unsafe or even be exposed to predators

2. Common Nest Box Sizes In Australia

Here are some popular nest box categories and who they’re best suited for:

Small Nest Boxes

• Species: Rainbow Lorikeet, Treecreeper, Red-rumped Parrot, Sugar Glider
• Hole size: 30–60 mm
• Box dimensions: Around 200 x 200 x 400mm (varies by species)
• Installation: Place high in trees or under eaves for protection from predators.

Medium Nest Boxes

• Species: Rosella, Australian Owlet-nightjar, Dollarbird and many more.
• Hole size: 60–100 mm
• Box dimensions: Around 250 x 250 x 400 mm (varies by species)
• Installation: Position the box 3–5 metres high.

Large Nest Boxes

• Species: Ringtail Possum, Galah, Brushtail Possum, Owls, Cockatoo and many more.  
• Hole size: 80–150 mm
• Box dimensions: 250 x 260 x 500 mm or (varies by species)
• Installation: These boxes are heavy. Secure them well and ideally mount in a sturdy mature tree.

3. Entrance Hole Size

In Australia, predators like cats, snakes, and even large goannas can threaten wildlife using nest boxes. While the overall size is important, the entrance hole is often the deciding factor for which target species will move in. For example:

• 30-60 mm: Small birds
• 60-100 mm: Rosellas and parrots
• 80-150 mm: Possums and larger birds

A hole that’s too large can invite predators, so aim for species-specific entrances wherever possible.

4. Other Considerations

• Placement: High and sheltered locations are safer from predators.
• Drainage and Ventilation: Small holes at the bottom keep the interior dry and cool.
• Emergency Exit: If you have concerns about other predators we have the option to add an emergency exit to the nest box for a small cost.
• Pick a safe spot: Away from strong winds and ideally facing east or south-east to avoid the harsh afternoon Australian sun.
• Check your boxes annually: for pests like mynas, bees, or ants. Also to make sure the tree attachment system is still secure without restricting the trees growth.

5. Variety of sizes

To get a natural mix rather than one or two species we recommend a variety of nest box sizes. The rule of thumb is 4 small nest boxes, 2 medium nest boxes and 1 large nest box.

Build a Backyard Wildlife Haven

Start with one or two boxes that suit the animals already living around you, like lorikeets in the suburbs or microbats near creeks. Over time, you can add more boxes in different sizes, and your backyard will quickly feel like a mini wildlife sanctuary.

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