To support future growth, Hamilton City Council is undertaking a major infrastructure project, the Southern Links project, to connect the city’s southern areas to the wider Hamilton and Waikato roading networks. The project involves a new four-lane bridge over the Waikato River, car and public transport access, roading links in and out of Peacocke, and cycling and walking routes. Committed to sustainable growth, Hamilton City Council looked to enhance important and sensitive natural environment features, including consideration of the Threatened Nationally Critical long-tailed bats.
As part of the Southern Links project, AECOM was engaged to deliver an Environmental Management and Monitoring Plan (EMMP) to identify how the project could ensure no net loss in biodiversity. The EMMP took three years to prepare with multiple ecological experts and input from various stakeholders, including Waikato Regional Council, the Department of Conservation, Stream Care Groups, and the Southern Links Tangata Whenua Working Group.
Understanding pekapeka behaviour
Long-tailed bats naturally roost in trees with cracks, holes, splits, or under loose bark. They are known to live in smaller social groups and often change roosts most nights. A key concern for the project was the loss of bat roosts and potential bat roost trees. The internal environmental conditions are important, especially during the maternity season and colder months when bats go into torpor, a form of semi-hibernation. Due to the scale of the project, some tree loss was inevitable. However, through strategic location and design choices, tree loss was minimised.
Evidence-based management
Eighty bat boxes (artificial roosts) with associated tree predator bands, designed to give the bat population additional predator-protected roost sites to offset the loss of trees with roost potential, were installed as early intervention and to build resilience in the local bat population prior to implementing the Project.
AECOM developed an effective bat box monitoring methodology, using innovative methods such as thermal imaging, endoscope, visual, and eDNA survey techniques to detect if bats were using artificial roosts and demonstrate that the environmental management efforts were effective. AECOM used thermal imaging to show the increased heat within the artificial roost, indicating that bats were present. The same thermal technology was also used to assess bat behaviour in areas where vegetation had been removed for construction along an important bat corridor on the Waikato River. By comparing bat behaviour at test and control locations, AECOM showed that the current vegetation removal and construction activity was not significantly impacting bat behaviour. AECOM also collected DNA samples from artificial roosts to test if bats were using the artificial roosts – the first time eDNA was applied in this way in New Zealand.
The current belief is that artificial roosts may be an ineffective short-term mitigation effort, with some studies showing a use rate of less than 5 percent over a short period. In contrast, AECOM demonstrated that 41 percent of the artificial roosts installed for this project were being used within only two-years post-installation.
Meaningful data
AECOM improved the visualisation of bat data, using the Flourish Studio platform to represent around 40,000 data points collected during the 2022 monitoring. These efforts showed that the ecological objectives of building resilience through early mitigation initiatives are being achieved and that current construction is not adversely affecting the receiving environment.
AECOM’s work will be published to allow learnings to be transferred to projects across the country and will contribute to scientific knowledge of the elusive endemic bat. The observations and methodologies developed are expected to help inform other environmental management plans considering how to minimise the impact of the gap between the loss of potential roost trees and the emergence of suitable roost trees through restoration planting.
