Creating Habitat: Nest Boxes and Artificial Hollows

Tree Hollows

Across Australia, there are about 300 Australian vertebrate species that rely on tree hollows. In the City of Parramatta our hollow-dependent vertebrate species include native birds, insectivorous bats and arboreal marsupials (see Table 1).

Tree hollows are used for shelter, nest sites, rearing of young and keeping cool on hot days and warm on cold days. Across the local government area (LGA) there is a lack of tree hollows due to past and ongoing vegetation clearing for urban expansion, development and tree risk mitigation. Whilst the planting of trees across the LGA is a key objective, the recruitment of trees containing hollows is a slow process that often takes more than 100 years, particularly for the formation of larger hollows.

To mitigate the scarcity of hollow-bearing trees, Council uses artificial hollows (roost and nest boxes, as well as mechanically created hollows into trees). These mimic natural hollows so to increase habitat for the native hollow-dependent fauna and to contribute to habitat connectivity to support viable populations. In addition, artificial hollows are also used as an educational tool to raise awareness and engage the community.

Table 1 List of City of Parramatta’s hollow-dependent wildlife

Arboreal marsupials

Flying mammals

Council's artificial hollow program

Council has installed over 450 nest boxes and roost boxes across the LGA, In addition, chainsaws have been used to carve entrances to internal hollows within dead trees (stags) to increase the range of naturally forming hollows.

One key aspect of the effectiveness of an artificial hollow program is ongoing monitoring. Monitoring provides important insights about box use and also enables the identification of boxes requiring repair/replacement and assist in implementing an adaptive management response where required. Residents are encouraged to observe what is happening with their local nest boxes and to share their observations with Council. These observations will be incorporated into Council’s overall monitoring program.

Effectiveness of artificial hollows

The longevity of artificial hollows has been raised as a potential issue in scientific literature. To ensure a best practice approach, Council uses boxes that are constructed from long-lasting materials, which includes the use boxes made from outdoor grade timber and recycled plastic.  We also take care that we use box attachments that are long-lasting and allow for tree-girth growth.

There is also the potential for boxes being used by exotic species, such as Indian myna (Acridotheres tristis), common starling (Sturnus vulgaris) and European honey bees (Apis mellifera). The annual monitoring provides insight into the level of box use by exotic species/non-target species and a management response may be implemented should box uptake be high by these species.

Types of artificial hollows

Whilst there is limited research on species-specific box designs, some guiding information is known for some species, such as box dimensions and entrance size. 

Recent research showed that commonly used bat box designs tend to be used infrequently and often by only one species (Gould’s wattled bat – Chalinolobus gouldii). Council has recently installed alternative designs with the intent to attract a greater number of species. It will be interesting to see if these designs will have some success. 

For arboreal mammals, Council has started to use ‘rear-entry’ boxes so to limit uptake by non-target species including exotic bird species. 

For more information on nest box designs:
•    Build your own Wildlife Nest Box
•    Birds in Backyards
•    Install a Microbat House

Biodiversity Strategy 2015 - 2025

Life in our City is City of Parramatta's Biodiversity Strategy 2015 - 2025, developed to protect our local environment. This strategy provides a framework to ensure biodiversity is conserved whilst recognising land use along with social, health and economic issues within our Local Government Area.

Read the Biodiversity Strategy 2015 - 2025:

• Summary
• Volume 1 Part A - Strategy & Actions
• Volume 1 Part B - Maps
• Volume 2 - Supplementary Information

Council is currently developing a Bushland Management Plan, an internal document for staff, contractors and volunteers. The Plan will guide the planning and implementation of biodiversity restoration and regeneration activities on Council managed bushland reserves and riparian zones.

For more information

Contact City of Parramatta's Natural Resource Team:

P:  (02) 9806 8280

E: bushcare@cityofparramatta.nsw.gov.au