Want to see more wildlife in your neighbourhood? Start by giving them somewhere safe to live. Read on to discover how nest boxes may be the missing link to a garden rich with local native birds, possums and microbats.

A western pygmy possum in a nest box.
A western pygmy possum poking its head out of a nest box. Photo: Elisa Sparrow.

What does a nest box do?

Many of our native birds and mammals rely on tree hollows for nesting and shelter. Unfortunately, the loss of old trees, which house these hollows, has led to a shortage.

Tree hollows, which occur in both living and dead trees, can take hundreds of years to become suitable.

Different animals have different requirements too – so for example, for a tree hollow to become the right size for a brushtail possum or cockatoo it can take more than 300 years.

Tree hollows aren’t just a place to stay safe, hidden away from predators, they also provide natural air conditioning in the scorching summer months – thanks to the tree’s transpiration. In the winter, they are also warmer than the frosty outdoors.

Without tree hollows – or an alternative – some species just cannot survive. That’s where nest boxes can come in.

How are tree hollows formed?

Tree hollows can be created by a range of things such as branches breaking off in strong winds, lightning strikes, fire or fungus creating a hole, and termites or other insects eating through the wood.

The size of the hollow opening can vary greatly – from as small as 2 cm in diameter (from one side of the hole to the other) to greater than 30 cm or more.

Fire can cause tree hollows to form quicker – and in younger trees – but generally it’s the older trees that are less resilient to things like insect attack.

If you think about how long it would take for an insect or fungus to work its way through a large tree branch, you can start to understand why it takes so long for a big enough hole to form.

Is a nest box as good as a tree hollow?

No – natural tree hollows are better, but nest boxes are better than nothing.

If you have the option to protect a tree – dead or alive – especially one with an existing hollow, that is definitely the best bet.

If your yard doesn’t have any natural tree hollows – or you think it could use some additional wildlife housing – read on to learn about using a nest box as an alternative.

A ringtail possum poking its head out of a nest box.
A ringtail possum in a nest box. Photo: Elisa Sparrow.

What is the difference between a nest box and a birdhouse?

Well, technically birds can – and do – live in nest boxes, so calling it a birdhouse isn’t exactly wrong.

However, if the term ‘birdhouse’ conjures up images of a little house that’s more aesthetically pleasing than it is designed for the needs of a specific bird species, that’s not really what a nest box is all about.

Nest boxes are purpose-made for the species that they are intended to attract and support. Even different bird species can have different requirements, so putting up a colourfully painted house won’t necessarily result in a pair of your favourite parrots moving in.

People hanging colourful birdhouses in a tree.
People hanging colourful birdhouses in a tree. Photo: Adie Bush, iStock.

Do all species use the same type of nest box?

No. Different species have different requirements – and not all species will use the same nest box all the time.

For example, ringtail possums will opt for a leafy nest aka drey most of the year but shift to tree hollows – or nest boxes – during the wetter part of winter and spring.

On the other hand, brushtail possums are what we call ‘obligate hollow users’, meaning that they need to find a suitable hollow or shelter of some kind every morning before dawn (because they’re active during the night). Without this, they cannot survive.

A ringtail possum in an alternative to a natural drey
A ringtail possum in an alternative to a natural drey. Photo: Elisa Sparrow.

Who will use my nest box?

Here’s some of the local native animals you could consider trying to attract with a suitable nest box:

  • ringtail and brushtail possums
  • rosellas, red-rumped parrots and other parrots
  • ducks
  • spotted and striated pardalotes, and other woodland birds
  • kookaburras
  • microbats (there are 8 different species found across metro Adelaide).

Purchase a nest box for the species that you want to attract or consider making your own – but remember you’ll need specific dimensions and some animals will even need things like a little ledge inside the box, below the entrance. It’s important to do your research thoroughly.

How high up should my nest box be?

Aim to install your nest box 4 m to 8 m off the ground to reduce the threat of dogs, cats, rats and foxes.

You will need to maintain the nest box, so place it at a height that you will be able to reach again – with the help of a ladder.

Does the position of the nest box matter?

Yes – and it depends on what species you’re trying to attract too.

Different animals even have different preferences for how much leafiness is around the box too. For example, parrots don’t like a lot of greenery around their home but possums do. So, your absolute best bet is to research what suits the species you want to attract.

Check out some recommendations for box orientation to help you find the perfect spot.

One of the many species that rely on tree hollows – the striated pardalote.
One of the many species that rely on tree hollows – the striated pardalote. Photo: Martin Stokes.

How do I maintain my nest box?

To make sure the nest box is serving the purpose you installed it for, you’ll want to check it relatively regularly – at least a few times a year.

Structural integrity is the main thing you want to be sure of, to make sure that the nest box is safe for your fluffy and furry neighbours to use.

This might mean checking the screws are still in tightly and potentially changing any attachments used to connect it to the tree, if they look damaged.

The last thing you – or its residents – want is for it to fall out of the tree.

Honeybees will prevent any other species moving in, so if they take over your nest box, you might want to call a bee keeper.

Do I need to do anything else?

Maintaining large trees on your property is an important part of creating a wildlife-friendly backyard.

In addition to providing shelter for your new flatmates, you’ll also want to give them some food options – imagine moving into a suburb with no supermarket!

Local native plants that have flowers, fruits or berries, as well as native grasses, can provide an important food supply, not just for the species using your nest box(es) but those visiting your yard too.

The structure of your garden – whether there are different layers of vegetation – makes a difference too.

Ideally you want to have a dense layer of local native shrubs around trees with hollows or nest boxes because this will help deter predators.

Just having one giant tree with a hollow or nest box surrounded by lawn will make it easy for the likes of feral cats to climb up and have a look – or nibble on – what’s inside the nest.

Find plant suggestions in our Adelaide or coastal gardens planting guides. Note that the coastal guide is suitable for anyone within 5 km of the coast.

5 tips for encouraging wildlife into your yard

  1. Grow plants that are native to your suburb.
  2. Plant species that are a range of heights.
  3. Choose a range of native plants so that you have flowers all year round.
  4. Manage pets responsibly e.g. keep cats indoors.
  5. Minimise chemical use.
  6. Provide a water source – like a regularly-cleaned bird bath.

For more ideas, discover how to make your butterfly friendly, attract more native bees or create a yard that welcomes native birds.

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