Trapping in action

Forest & Bird volunteers and staff worked hard over summer to protect and monitor precious long-tailed bat roosts in Marlborough. By Lynn Freeman

Forest & Bird’s Te Hoiere Bat Recovery Project in Pelorus Bridge-Rai Valley, Marlborough, demonstrates the value of a well-managed and intensive trapping programme. 

Earlier this year, I travelled there to see the team’s work at first hand and hear about some of the challenges of carrying out predator control in a remote area of stunning native forests and wild rivers. 

Their conservation mahi is improving the survival chances of the charismatic pekapeka tou-roa long tailed bat, our “Bird of the Year” winner in 2019. 

At DOC’s Pelorus Bridge Scenic Reserve, thanks to our generous donors, Forest & Bird has been protecting the pekapeka tou-roa for more than a decade. 

At the nearby Rai Valley, a new Forest & Bird managed trapping programme, funded by Jobs for Nature, began in November 2023. It was designed by DOC and implemented by Ngāti Kuia in DOC’s Carluke and Ronga Reserves.

Shannon and Sarah Huntley, of Ngati Kuia, established the initial trapping grid infrastructure, and the Society recruited Abigail Hill to oversee the trapping programme. 

She ran the project’s traplines in the Rai Valley last year, monitoring 259 rat and possum traps on 20ha in the two reserves. 

This hard work has paid off. Over the past summer, our bat recovery team caught and banded the highest number of individual pekapeka bats in the Pelorus, Carluke, and Ronga Reserves since monitoring began seven years ago.

Pekapeka tou-roa (long-tailed bat). Image: Franco Elgueta Rivera

The Carluke and Ronga reserves pose a particular challenge for those trapping the predators that threaten the bat population. They have a habit of flooding.

“When the river overflows its banks, it pushes dead logs across the forest floor and risks dislodging the traps,” Abi explained.

“Some of the traps that we placed on the ground we attached to a large peg. We have still had a few traps ripped out of the ground and carried away, stake and all.”

Even when there’s no flooding, the densely forested reserves are prone to pervasive dampness, which can turn bait used in the traps mouldy.

“Keeping the traps as clean as practical is the goal,” added Abi. “They may be associated with filth, but rats keep themselves clean and like a tidy home.”

There’s a good reason why ship rats are “enemy number one” in this piece of paradise. They are arboreal, and running up tall branchless trees to grab young bats in their roosts is all in a day’s work.

In 2023, the team got footage of two rats zooming up a tree as bats were emerging from a maternal roost. It’s disconcerting to watch, especially knowing that maternal roosts can host 50 or more bats during the breeding season and there would be no escape if a rat snuck in.

Possums are also nocturnal tree climbers, but at this stage, while it’s good to get rid of them, they are not known to pose nearly as big a threat to the area’s pekapeka tou-roa.

Abi uses a combination of Victor rat traps, DOC 200s, and Goodnature A24s in the Carluke and Ronga Reserves.

“The first two are conventional snap traps of different sizes, both set off when the target animal applies pressure to a trigger plate. They’re found on the ground in extra-long wooden boxes to keep out weka,” she explained.

Abigail Hill (second from the right) with members of the Te Hoiere Bat Recovery team: Henry Neas, Aubrey Tai, Flynn Cowie, Oren Cranna-Powell, Daria Erastova, and Clare O'Rouke (front). Image: supplied.

“The A24s are self-resetting, tree-mounted traps well suited for rodents.”

Abi has numerous rat bait options, including cinnamon-based, peanut butter-based, and treaclebased baits, plus Erayz freeze-dried rabbit, and an egg supplement that is so whiffy she dares not spill any on herself or her vehicle.

Generous donations from keen volunteers and supporters have allowed dozens of AT220 traps to be installed in a block in the Pelorus Scenic Reserve where a large number of bat roosting trees have been identified.

These trees are protected by a Forest & Bird eco-team, a group of dedicated local volunteers assisted by three staff members led by Clare O’Rourke, who carry out predator control in the Pelorus Scenic Reserve.

An added bonus of the AT220s is that they are self-resetting, so they don’t require constant servicing, reducing the volunteer time required to keep the network in tip-top shape.

Testing the density of traps needed to effectively protect pekapeka tou-roa has been another aspect of Abi’s work. 

The local DOC office recommended a 25 x 25m trap grid in areas with known bat roost trees. This is a super high-density grid, but with little known about how much predation pressure pekapeka tou-roa can handle and the importance of this habitat for the taonga species, caution was warranted.

It’s paid off. Rat catches were initially high but plummeted within a few months of the traps being set. By January 2025, rodent presence had fallen to below detectable levels.

“The reduction of rats, the ship rat in particular, and the following decrease in mustelid numbers will have a positive effect on bats,” Abi added.