Mardo Reserve 7

Native Australian trees (especially gum trees) are hollowed out when the internal heartwood is exposed to the elements. Lightning, fire, wind, rain, bacteria, fungi and insects all contribute to hollows being formed. This process is incredibly slow – it takes at least 100 years to naturally form a hollow suitable for only small animals (lizards, bats, small birds) to occupy. Larger species like owls and Black-Cockatoos need large tree hollows which take at least 250 years to form. In some parts of Australia around 60% of native animals require tree hollows of some kind in which to sleep or raise young. Therefore, trees bearing hollow branches (known as ‘habitat trees’), are very important for wildlife!

Keeping large, old, hollow-bearing trees is the best step toward conserving the fauna that depends on them. However, in areas where clearing has already occurred, there are short-term solutions. Nest boxes are artificial tree hollows attached to living or dead trees. They have been shown to form a successful substitute for natural tree hollows and are being used in many conservation projects worldwide. A nest box can simply turn a tree that is 20 years old into one that is 200 years old, with relatively little effort. Each box is designed to suit a particular species of animal, depending on its size, shape and nesting or roosting requirements. Several designs are present in Mardo Reserve.

The nest boxes installed in Mardo Reserve were all made by Mundaring Primary school students following the design features and materials used for iNSiGHT Ornithology nest boxes.

For more information, visit the Re-Cyc-Ology Project website:

Nest Box Designs

The small square boxes are designed for small mammals including the Mardo, and if present, the Brush-tailed Wambenger. The entrance is a small hole which faces the tree, providing extra protection from the elements and preventing other non-target species from entering. An animal wishing to enter the box can climb vertically along the trunk and squeeze inside from the back. Mardo will curl up among leaves and bark strips inside the box, while Wambengers build a dome-shaped nest from leaves and grasses.

 A small nest box designed for Mardo

 Looking inside a Mardo box you can see the entrance faces the tree trunk.

Bat boxes are tailored to suit several species of native microbat. They hang on the side of tree trunks and have a small slit entrance at the bottom. This is positioned just above a ‘landing pad’ where a bat can cling on with its fingers and climb upwards into the box. Bats are nocturnal and roost during the day beneath bark, in cracks in trees, and sometimes in walls and roof spaces. They can roost alone or communally, huddling together for warmth in the colder months.


Small vertical boxes are designed for parrots including the Red-cap and Ringneck, though sometimes possums will squeeze inside them too. Most birds do not use tree hollows unless they are nesting, and species which might occupy them are only those which select natural tree hollows. (Other birds such as magpies, honeyeaters, wrens and the Willy Wagtail build their own nests and will not use boxes). Parrots enter the box and climb downwards using a ladder placed inside. They build no nest but instead chew bark and wood chips to make a soft bed on which to lay their eggs.

Two designs of medium-sized nest box were placed in Mardo Reserve, to cater for the needs of species such as possums and owls. These are either a square shape with a hollow entrace, a design that possums use, or a larger, vertical box with a slit entrance and no hollow. This type of box has been used by ducks and owls in the past.

Large vertical boxes are made for Black-Cockatoos, which, of all the species requiring hollows, are probably in most urgent need of them. These boxes are over 1 metre deep and are designed to replicate a large vertical trunk which has broken off and is hollow inside. The box is quite deep which protects the occupant from weather, and a mesh ladder allows animals to climb in and out. You can watch a video of a Carnaby's Cockatoo chick inside a nest box by clicking here.


                                   Bat boxes have a tiny slot entrance.                                                       A small vertical nest box for parrots.


                                   A medium nest box for possums.                                                       A medium nest box for ducks or owls.


                                        Large nest boxes for Black-Cockatoos have been already used by Australian Wood Ducks.