The loss of hollow bearing trees has now been declared a key threatening process by the NSW Scientific Committee. This means that the loss of hollow bearing trees is recognised as having a direct link with the loss of certain native wildlife species.

In urban areas natural tree hollows are limited in number especially as hollows generally form in trees that are dead, dying or have suffered some damage or insect attack.  These trees are often seen as a danger to people and property and are therefore readily removed.  Where this is the case next boxes can provide a den for animals dependent on hollows.

Nest boxes should not be considered a suitable replacement for tree hollows, but a temporary measure, or as a supplement where hollows are already lacking.  Hollow bearing trees should still be retained and planned for the future wherever possible.

In order to mitigate the loss of hollows in the case of necessary tree removal resulting from development applications, Council regularly imposes conditions to install nest boxes. This gives the benefit of creating additional nesting and roosting habitat where hollows may be lacking. If you have conditions for provision of nest boxes on your development application consent, the following information will be very useful.

Design

The design of the nest box will usually need to be specific for the targeted species.  Dimensions of the box (volume, depth and wall thickness), internal structure, position and dimension of the entrance and construction materials all need to be considered.  As a general rule the dimensions for the entrance hole should be no larger than required for the body size of the target species.  This reduces the risk of predation and use by exotic species. 

Small species such as Feathertail and Sugar Gliders choose hollows that are only slightly larger than their bodies to prevent larger animals attacking them or taking the site.  Larger species such as Brushtail Possums and Greater Gliders need hollows with entrances greater than 5cm.  Common Brushtail Possums generally choose hollows with 12-15cm entrances.

Construction

Nest boxes can be made from timber or exterior-grade plywood (2-19mm is ideal).  To waterproof the box, screw the ends together and paint the exterior.  Do not paint inside the box.
Sawn timber boxes should be well ventilated and have good drainage (a small gap under the roof or a few small holes in the floor). 
Avoid using treated timber, toxic paints, or chipboard and make sure there are no sharp protruding edges or nails.

Myna and Starling Proof Nest Box

(Taken from 'The Nest Box Book' by Jim Grant, Gould League)

This design has been suggested by experts and trials have shown that it is likely to work.  It is based on the idea that starlings and mynas like to see a hollow and fly directly into it, but rosellas, for example, are used to climbing to get access to natural tree hollows.
The design shown is for rosellas but this method can probably be applied to many nest boxes. 

 
The distance between the baffle and the front of the box is probably important, and must be wide enough to allow the animal to climb into the hole and narrow enough that starlings cannot fly under it and up into the hole.

Location and Installation

Nest box locations should be quiet, up high (over 4m), safe from predators (e.g. cats) and sheltered from prevailing winds and the midday sun.
The box itself should be positioned so that the animal(s) can easily get in and out and can easily reach and climb onto nearby branches.
Nest boxes may also suffer invasion by feral bees, ants and non-native bird species such as Indian Mynas.  In this case, the nest box may have to be temporarily removed.
Cats and rats can also be a problem in some areas.  To prevent these animals accessing the nest box, a metal sheet (approximately 1m wide) can be wrapped around the base of the tree or pole ensuring the metal sheet is high enough to prevent predators jumping over it.

Monitoring Your Nest Box

Monitoring your next box will give you a great indication as to its success or otherwise.  This can be easily achieved using binoculars and a notebook. 
The collection of information on faunal activity can provide invaluable information as well as being a rewarding experience.
Monitoring nest boxes is also necessary for the control of pest species such as cats, rats, bees, insects or Indian Mynas and other exotic birds. 

Fauna Species within Pittwater that use Nest Boxes

Updated: 02 Dec 2011