Fiordland bat Diaries – The Ettrick Burn Part 4

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 four we join the team just before Christmas, catching up and reviewing the monitoring footage.

More rain, more delays, we are starting to run out of time before Christmas. But there is just enough time for one final quick trip. Back at our roost tree we change the old batteries for new ones, swap the SD card and get a download from the data logger. Two transmitters are still in there but by now we aren’t sure if they are still on our bats or have dropped into the guano pile that fills the bottom of the roost cavity. Then we are off to climb and remove the video camera from another tree we had previously set up. The footage from here had only one lone bat departing, so it’s time to give up on this tree.

Back at the hut we watch hours of footage counting bats and look at what’s on the datalogger. One of the questions we have about this colony is whether they have always been here hiding away, or whether they have branched off the Eglinton colony which is 40km away, a result of that population growing due to sustained predator control. In the new year we will be undertaking our annual monitoring of the Eglinton colony where over the past 15 years almost 3000 bats have been individually tagged with microchips, the same as the ones you put in your cat or dog. If the Ettrick Burn bats had split from the Eglinton colony then chances are some of them would have microchips.

We have hand scanned every bat caught mist netting with no tags found, but the real test will be from the datalogger. At the tree we have set up an aerial around the roost hole to scan every bat as it flies in and out. When we look at the file it too comes up negative for tags. Maybe they have always been here, hanging on. It does makes you wonder, are there other little populations hanging on out there that we don’t know about? No one has ever conducted a proper search nation wide for short tailed bats.

Our transmitter bats turn up in couple more trees, which when climbed leads to the transmitter sounding far off in some unobtainable limb, leaving us unable to tell if these trees are communal or not.

More videos, more rain, the river is a torrent again. The bats stay roosting in our one known communal tree, though there must be another out there somewhere. And then it’s nearly Christmas, time to pack up and head home for the last time. In the end we collected 8 nights of useable video footage, but the count is never above the initial 207. For a short tailed bat colony this is small (the Eglinton counts are between 2000-3000) but it’s something, and the population is large enough that with sustained rat control it should be able to recover. However, it is too late for rat control to deal with the 2019 mast/plague but there are plans afloat for the next beech mast.

We make a final trip to our old faithful tree. The equipment on the tree comes down, then the tents packed up, the hut cleaned, and another game of tetris packing the helicopter. It’s goodbye for now, we hope to be back next year and find our bats hanging on.