Waikato Expressway, Cambridge Section - it's a bat tale


It’s become a bit of a bat tale on the Cambridge Section of the Waikato Expressway project, one that will roost long before this new section opens in 2016, says the NZ Transport Agency.

Extensive monitoring is underway along the length of the Cambridge Section route into the elusive small aerial insectivores, being the long-tailed bats that have been identified as roosting in stands of mature and exotic trees on some parts of the proposed Cambridge Section route.

Not a batty tale the NZ Transport Agency would normally be involved in, but for Project Manager Raj Rajagopal and contractors HEB Construction a bat management plan is being put into action with collaboration with Waikato Regional Council and the Department of Conservation to ensure this elusive and rare species to New Zealand is protected.

From monitoring already undertaken - HEB Construction’s environmental manager Simon Cathcart says 26 stands of trees along the 16 km section have been identified as having high bat activity with one site of bats roosting in mature oak trees between Discombe Road and Hautapu Road.

Mr Cathcart says the long-tailed bats typically roost in select mature native (e.g. kahikatea) and exotic trees (e.g. willow, pine, eucalypt, alder) that offer suitable roosting cavities such as split bark and tree knotholes.

Hamilton City (and areas to the south of the city) is now regarded as the only city in New Zealand confirmed as still supporting a local population of long-tailed bats.

Mr Cathcart says “We now have a good understanding of the distribution of long-tailed bats in the Cambridge landscape largely as a result of this Expressway Project.”

Project Manager Raj Rajagopal says further surveys were required to assess the importance of key roost sites for bats, investigate their response to the existing State Highway and also potential response to the changing landscape.

Mr Rajagopal says there will be on-going collaboration between all parties as the project progresses to ensure that effects of the Project on bats are minimised and mitigated, and also to learn as much as possible so that this can be applied on future Projects.

“There will also be on-going monitoring during and post construction to assess how bat populations have responded to the new road.”


Editors note:

Where are the bats likely to go now some trees have been removed?
The bats are likely to use other trees in their home range, which can be 5000ha. Long-tailed bats naturally switch between different roosts sites i.e. they typically make use of several roost locations at different times within their home range.

How many bats were living in the trees?
This is very difficult to determine. Monitoring bat activity using automatic detectors or hand held detectors can tell you that bats are present and the level of bat activity in a given area but it cannot tell you how many bats are present. The recording of 100 passes in a night by a bat detector could be 100 bats passing the detector or a single bat making 100 passes past the detector.

How big is the population of bats thought to be on the Cambridge Section?
Nobody knows how large the bat population is along the Cambridge Section as they are very difficult to study due to their cryptic nature.

We have a reasonably good understanding of where they occur or are most likely to occur in the landscape; however, we have no idea as to actual numbers. They are found widely in the Cambridge landscape with gullies and the Waikato River corridor being key habitats. They are also found in stands of mature exotic and native trees as well as the large tracts of forest e.g. Mangatautari and Pirongia. They tend to be absent from areas where there is minimal tree cover and urban areas, although they may be present in urban fringe areas.

I understand any trees that were used for roosting have been left untouched. Why is that?
Certain trees along the corridor have been identified by visual inspection as potentially containing bat roosts and have been left standing pending monitoring prior to removal. These are mainly the older trees with cracks and crevices which bats like to live in. There are about 26 stands of trees along the entire 16km length of the Cambridge section which we are monitoring closely. Of these 26 stands only three have shown any potential roosting activity and these are still being monitored. Trees identified as having roosting bats within are left in place until the bats vacate to avoid killing the bat during tree felling.

How many bat roosts have been removed as part of the Cambridge project?
None to date.