Monitoring reveals previously undiscovered long-tailed bat roosting sites

Thursday, 14 February 2019

Every day for the last two months, Gillian Dennis has set out before dawn in search of long-tailed bats. 

The mysterious mammals are small, dark, nocturnal and trying to catch them involves a lot of patience.

As the manager of Forest & Bird's Te Hoiere/Pelorus Bat Recovery Project, Dennis is behind the push to get a better understanding of the bat population in the area.

In the last two months, bats have been located in 12 different trees at the Brown River Reserve and Carluke Reserve near Rai Valley.

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'Neither of those sites were on the radar as being roosting habitats so that is pretty cool.'

Previous acoustic surveys in the area had shown that bats were present, but couldn't provide any idea of their population size and whether they were just feeding or also roosting in the area. 

Dennis and a team of volunteers have been tracking bats at dawn and dusk near the Pelorus River since early December. 

Long-tailed bats forage for food at night, then head back to their roosts at dawn.

During the monitoring period, Dennis said the aim was to catch bats and attach tiny radio transmitters to those who could cope with the weight, so they could follow them back to their roost.

Ideally, they would place a trap in front of the roost, catching the bats inside it to find out how many were living there. But the roosts were all at least 20 metres off the ground in dense canopy so it had been difficult to get an exact count of how many bats were in the area. 

Long tailed bats are one of only two native land mammals in New Zealand. They have the same threatened status as the kākapo.

Dennis said it was not known that bats were hunting and breeding in the area so it was a really special discovery, and it was important to protect the habitat as best as possible.

While it has long been known that bats frequent the Pelorus area, their population and whether it's rising or falling is unknown.

'Bats were widespread and abundant before European settlement but with the introduction of predators and the loss of forest habitat they have just been dropping away.

'Places where they once would have had strong holds, they are now kind of just hanging on.'

Ecologist Brian Lloyd had previously surveyed long-tailed bat population in the top of the South Island and found there were sizeable populations in the Pelorus River catchment and on D'Urville Island. 

Dennis said the new roosts were about 10 kilometres down the road from where Lloyd had first identified a population at Pelorus.

An extensive trapping programme had since been implemented in the area in a bid to protect the bats.

Dennis said without knowing the population size or the survival rate of the bats it was hard to gauge if the extensive volunteer efforts were having an impact on the species. 

It was intended that the monitoring would include the original Pelorus population but Dennis said they had been unable to catch bats at that site.

It was the first time such comprehensive monitoring for long-tailed bats had occurred in the area and Dennis said it would support conservation efforts. 

Referred to as a 'bat expert', Dennis has been working with bats for the last 13 years. Her first interaction with a bat was in Fiordland, 20 years ago. It was one that would change the course of her life. 

'I had been working with birds up until then and I think I realised bats didn't get a lot of attention, there was so much about them we didn't know. Every time you asked a question, it raised 10 more questions about them.'

She said the Pelorus long-tailed bat population was 'pretty special'. Monitoring was finished for the season and would resume again next summer.

The Te Hoiere/Pelorus Bat Recovery Project is run by Forest & Bird and received funding from the Department of Conservation (DOC) community fund and the Rata Foundation.

It is hoped more funding can be secured to enable acoustic lures to be used in future monitoring to improve the chance of catching bats. 

Donations to the project can be made through the Forest & Bird Givealittle page.