Fiordland Bat Diaries: The Ettrick Burn Part 3

With two species of native bat living in Fiordland local rangers undertake monitoring in order to protect and learn more about these special little critters. They are on the hunt for a new short-tailed bat colony in the remote Murchison Mountains. In part three we join the team on their second trip after having been rained out.

To say it rained would be a bit of an understatement. Lakes Te Anau and Manapouri are drowning picnic tables by the dozen and the South Island has been cut in half by flooding. We are delayed returning by a week, but with the promise of some fine days it is time to head back in. One benefit of steep sided rivers is that while the Ettrick Burn rapidly turns into a torrent it also quickly drains and by evening we can safely cross the river joined together.

Radio tracking from the helicopter on the way in proved unsuccessful in locating our transmitted bats but on our way to another evening of mist-netting we pick up the signal from one, TX10, and find our first known roost tree. It’s too dark to do any more at this tree but this evening’s mist netting turns up exactly what we are after, an obviously pregnant female who gets a transmitter too, TX30.

Now that we have found a roost tree it’s time to lug our tree climbing and recording equipment up valley, that’s three 20kg packs back through the river, over the windfall and an hour and half up the track. Of course when we get to the roost tree TX10 is no longer there. We follow the signal back across the river and up the hill to her new roost tree, but it sounds like she is somewhere at the top and our bat sense tells us she is probably solitary – not worth the effort of climbing. Time to dump the gear back on the track and head home for another day. Our spirits are lifted watching a family of whio/blue duck on a rafting trip down stream, five juveniles escorted safely through the rapids by mum and dad. Masters of the eddy they make kayakers look like amateurs.

A new day, a new bat. TX30’s signal is located in a tree up valley, now we are onto something. We climb trees on static ropes, these go from the end we climb on up and over a sturdy fork or limb before heading down to the ground on the other side where they are tied off on another tree. How does the rope get there you say? With a slingshot and fishing line! We fire a sinker up and over the desired fork, fishing line trailing behind. As the fishing line isn’t strong enough to pull the rope we use cord as the middle man, it’s an endless series of winding and unwinding. Safety checks all done it’s time for one of the team to head up and try and find the roost hole.

There’s a split in the tree half a metre long and no more than 5cm wide, I can smell the musky sweet odour which is distinctly short tailed bat, and it squeaks. These are the signs of a communal roost, this is what we have been looking for. Quietly as possible so as to not disturb them we set up a video camera and data logger, their cables run down the trunk of the tree so we can get the data and change batteries without having to climb the tree all the time. Technology is an amazing thing – once it took car batteries to power this gear, now we use lithium ion.

With rain on the way, another transmitter on for safe keeping and the roost camera remaining to do the important work it’s home time again. The first night’s footage of the communal roost shows 207 bats emerging for a night of foraging. This gives us our first minimum number of short tailed bats in the valley. It’s too early to tell how many more might be around, we don’t even know if we have found the main roost tree yet but it’s a start.

Follow the team in part four to see how the bat count goes.