Endangered microbats make a comeback along the Princes Highway upgrade
The Berry to Bomaderry Princes Highway upgrade project has delivered measurable biodiversity outcomes through the installation of artificial microbat habitats. A total of 38 bat boxes and caves were installed across 10 structures, reducing the impacts of construction while supporting the local microbat species.
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These artificial habitats have supported the existing microbat colonies and enabled an increase in the number of individuals recorded. Since 2023, post-construction monitoring has shown a rise in the number of microbat individuals compared to the pre-construction baseline.
The monitoring also confirmed breeding activity including the establishment of maternity roosts, providing insight into the effectiveness of the artificial habitat in sustaining the local microbat population.
The outcomes demonstrate the project’s effective use of evidence-based mitigation measures and the implementation of tailored solutions to deliver long term biodiversity success.
Approach and implementation
The project’s biodiversity mitigation combined ecological expertise with engineering design to create artificial habitats suited to microbats, particularly the threatened Southern Myotis. Tailored bat boxes and caves were designed to provide suitable roosting conditions and were integrated directly into bridge structures through collaboration between environmental specialists, engineers and local stakeholders. Key actions included:
Designing diverse habitat types
Engaging with ecologists to design and install a diverse range of artificial habitat types, such as traditional wooden boxes and Hebel (concrete) structures, to optimise thermal conditions and integration within the bridge infrastructure.
Integrating habitat with infrastructure
Working closely with bridge engineers to seamlessly incorporate the bat boxes and caves into the 10 different bridge structures, ensuring the habitat was fit-for-purpose and complemented the overall design.
Establishing baseline data
Conducting comprehensive pre-construction surveys to establish baseline data on the existing microbat population, informing the design and placement of the artificial habitat.
Implementing a post-construction monitoring program
Implementing a structured monitoring program, with twice-yearly (February and November) inspections from 2023 to 2025 to track occupancy rates, population numbers, and the overall condition of the habitat.
This collaborative, evidence-based approach ensured mitigation measures of the project's impact on the local microbat population were tailored to the microbats needs.
Outcomes and impacts
Monitoring over the past 2 years has provided quantifiable data on the success of the artificial habitat installation.
The effectiveness of the artificial habitat:
- 87% of the 38 bat boxes and caves were used at some point since installation.
- Average occupancy rates were 94% for Hebel boxes and 100% for timber boxes.
- 286 microbats were recorded in February 2025, exceeding the target of 25% of the original 69 microbats recorded during pre-construction surveys.
- Maternity roosts were identified, with Southern Myotis pups recorded in multiple boxes during all post-construction surveys.
Broader outcomes:
- The initiative strengthened Transport’s understand of habitat design, with timber boxes proving more effective and easier to monitor than Hebel structures.
- Design issues were identified with some bat caves where water ingress reduced occupancy, leading to recommendations for improved placement and construction methods.
- The growing microbat population contributes to ecosystem health, as these insectivorous species play a vital role in natural insect control.
- Collaboration on habitat design and monitoring strengthened relationships with ecologists and local stakeholders.
Lessons learned and future considerations
Through these experiences, Transport has gained several important insights that can inform future initiatives to mitigate the impact of infrastructure projects on sensitive ecological populations, such as microbats.
Optimising the artificial habitat solution
The installation of the artificial habitat has been successful, with the microbat population increasing over the post-construction monitoring period. However, issues such as water ingress in some bat caves highlighted the need to refine design and placement to improve long-term suitability.
Timber vs Hebel bat boxes
The timber bat boxes have proven to be more effective than the Hebel (concrete) structures, with a slightly higher average occupancy rates of 100% compared to 94%. The timber boxes are easier to monitor, whereas the Hebel boxes require the use of a camera stick to be inserted into the box, which can be more intrusive and disruptive to occupying microbats.
Bat cave design and placement
Some of the bat caves installed within culvert structures have exhibited issues with water damage and leakage, resulting in lower occupancy rates compared to the bat boxes. This has highlighted the importance of carefully considering the design and placement of these habitat types to ensure they remain dry and suitable for microbat occupation.
Sustaining success
Recommendations include installing additional boxes to replace the Hebel structures, investigating the causes of the cave leakage problems, and maintaining the regular monitoring regime to sustain the success of the artificial habitat.
The Berry to Bomaderry project demonstrates how integrating artificial habitat solutions into infrastructure design can reduce impacts on threatened species and deliver lasting biodiversity benefits, offering practical insights for future projects.
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