Over 300 species of our native fauna utilise tree hollows for nesting or roosting, with the size of the hollow depending on the size of the animal. It can take up to 100 years for a tree to develop suitable hollows and up to 400 years to develop hollows that can be used by larger wildlife such as possums and owls.
While nest boxes can never replace an old growth tree with its diversity of hollows, they can, with appropriate management, provide a benefit for some wildlife species in areas where these trees have been lost.
Hints for installing nest boxes
Identify the target species you wish to attract and install the appropriate nest box, remembering that most species will utilize more than one ‘hollow’. Research has shown that our possums and gliders occupy more than one hollow over their home range, with Squirrel Gliders requiring a minimum of five hollows per colony (two to nine individuals) and avian species such as the Owlett Nightjar using up to 23.
Factors such as hollow design, positioning, size of entrance, wood thickness, width and height of box is critical in influencing occupancy.
It's important to consider the following:
- The box should be placed in a shady position with its opening facing away from the prevailing weather. It is important to provide a summer and winter ‘residence’ as hollow dependent mammals will change hollow locations depending on seasonal influences.
- If possible, place the box level with a branch in the tree to provide easy access to the tree.
- Securely fix the nest box to a tree in, or near, your yard. Place it at least 4 metres (12 feet) from the ground to keep it out of reach of domestic cats and dogs.
- It was once considered best practice to secure nest boxes with a bolt directly into the tree; however it has been found that the reaction from the tree to this ‘foreign body’ exacerbates the rusting process, shortening the life of the nest box and creating a safety issue.
- Place the box in a position that is easy to access for monitoring and maintenance.
- It is recommended to attach the box using coated wire or threading the wire through a rubber hose where it contacts the tree. Creating a zigzag pattern in the wire at either end of the join will also allow for expansion as the tree grows.
Maintaining nest boxes
Natural hollows have microorganisms which play an important housekeeping role by helping to break down leaf and waste matter. Nest boxes do not have this and as such, their bases tend to rot out. It has been found that on average, nest boxes will require replacement every 5yrs. Nest boxes can also be prone to invasion by feral species which will have to be removed before the boxes are usable by our native fauna.
Simply placing a nest box in your garden will not bring in wildlife. You will also need to create the appropriate habitat for them, providing preferred food and shelter trees as well as water.
Monitoring your nest box
Monitoring the usage of your nest box is best undertaken by observation. Sitting quietly and observing your boxes on dusk can show you who is coming and going.
Another effective method is to observe the ground beneath your boxes for telltale scats (droppings) this is particularly useful when monitoring avian and bat boxes.
Check the entrance to your nest box – spider webs across the entrance will indicate lack of use. You can tell if a parrot is using the box as there will often be visible chew marks across the entrance.
On smooth barked trees, scratches will indicate movement up your tree and in some cases, a well used pathway will become evident.
In the case of gliders, a smooth, worn patch of bark will indicate where gliders are landing or taking off from - a glider landing pad.
Pots for Possums
You can provide a quick and easy nest box for possums by using pot plants. Connect the openings of two large plastic pots (270mm or larger) with cable ties - you will need to drill holes to thread them through. Then simply cut a 110mm hole in one end and line the inside with material, shredded paper or mulch. Secure it safely in a shady tree.
Ringtail Possums do not live in hollows, but rather, build their own nest out of leaves and twigs, called a drey.
You can make a drey for your ringtails by attaching two lined wire hanging baskets together with cable ties to form a round ball. Removing a section of wire in the font (80mm) and at the back provides them with an entrance and exit. Secure your drey in dense tees such as a Callistemon.
Providing more than one drey throughout your yard will help increase uptake, as ringtails will use up to 6 nests throughout their home range.
Insectivorous, or micro-bats, are valuable neighbours to welcome into your yard, with a single bat capable of devouring up to 4000 mosquitoes overnight. These bats occupy tree hollows, tuck themselves under loose bark and squeeze under caps on fence posts. You can provide easy budget accommodation for them in a number of ways:
An old garden umbrella (closed) positioned in your yard can provide accommodation for insectivorous bat species.
Another option is to use recycled plumbing pipe. Place a cap on top of the pipe and hang non-fraying material on the inside to enable them to hide in the folds. This can then be hung up in a tree or under eaves.
There are a number of companies that make nest boxes and they can also be bought from some pet shops and produce stores. You can also find many designs and ideas in bookshops or on the internet. Below are some resources that you might find useful:
- The nest box book – by the Gould League
- Nest boxes for wildlife, a practical guide – by Allan and Stacey Franks.
Contact the Redlands IndigiScapes Centre to learn more.
Phone: (07) 3824 8611