Lots of Batty Things

Recently I’ve had a lot of bat-related things going on. Three weeks ago, on July 21/22, I coordinated the winter survey for Southern Bent-wing Bats in South East South Australia. The caves in the region are split into two areas, the Lower South East (which includes Naracoorte and the surrounding caves) and the Upper South East (which includes Mt. Gambier and the surrounding caves). The survey took months to plan and was a coordinated effort between the South Australian Department of Environment, Water and Natural Resources, or DEWNR (formerly known as the Department of Environment and Natural Resources (DENR)) and the Victorian Department of Sustainability and Environment. Since the bats don’t recognize state boundaries, they use caves in both South Australia and Victoria. We wanted to get as accurate a winter count as possible, so of course we wanted to survey all the known caves. In South Australia this meant surveying 39 caves in one day (well, we had to survey a few caves the next day due to the logistics of accessing them). The idea of surveying in one day was to minimize double-counting of the bats, as they may move between caves overnight. Unlike in very cold areas, the bats here only go into torpor and not full hibernation. They often come out of their over-wintering caves several times in the winter if it’s not too cold and if there are insects out for them to feed on. They may also switch roost sites during this time too.

It took months of planning and several phone conferences to get everything in place. I had to contact cave landowners for permission to access their caves, assign volunteers to survey teams, distribute information to volunteers about the count, and coordinate the Upper South East volunteers on the day of the count. In total we had about 30 people help with the South Australian side of the survey, including volunteers from the Cave Exploration Group SA Inc (CEGSA), Friends of Naracoorte Caves, University of South Australia, Flinders University Speleological Society Inc (FUSSI), and staff from DEWNR. Thank you to everyone who helped!

We lucked out with a beautiful day for the survey. Each survey team consisted of 2-4 people (we kept groups small so as to minimize disturbance to the bats) and was responsible for checking several caves. Chris and I headed off with Mick Dennis, a member of the Friends and a skilled rope person, to check five caves around Naracoorte. The first cave we visited had a nice surprise for us. We found several large clusters of bats, totaling a bit over 5,000 bats. They were only about seven feet from the ground. We could have plucked them from the ceiling! Chris made a cool discovery among the massive cluster: a banded bat. Unfortunately we couldn’t read the band, but it was neat to see. The bats were quite awake when we arrived, and seemed in good health. Because we surveyed in July instead of June like in previous years, the bats were more active and were likely flying out every night to feed. There have been lots of tiny moths around Naracoorte at night, which would provide a perfect food source for the bats.

After the survey I collected the data sheets from all the teams, and now I’m in the process of writing up the results in a report. We found a total of 15,478 bats in the caves in South Australia (I don’t yet have the results from the Victorian side of the survey). This is obviously far less than this year’s peak summer population at Bat Cave of about 40,000. Where are the rest of the bats? They aren’t all dying off during the winter, as the majority comes back to Bat Cave in the spring. Are they using caves we don’t know about? Are they roosting in parts of known caves that we can’t access/see? Are they over-wintering in structures other than caves? We don’t know. More research is needed to tease out the reason for this discrepancy.

From the preliminary results of this year’s survey, appears that more bats were using caves in the Upper SE compared to previous years. Again, I think that’s because this year’s survey was in July and the bats are likely starting to head back to the Bat Cave maternity cave for the spring. I will begin taking regular thermal imaging counts again at Bat Cave to see how the bats come back from their over-wintering sites, whether they come back gradually or all at once.

Speaking of taking more thermal imaging counts, now that my time here in Australia is coming to an end, I have to figure out how this project will continue once I leave. Monitoring the bats at Bat Cave regularly, over multiple years, is vital if we want to be able to make any accurate judgments about the status of the species. I’ve spoken with the Friends of Naracoorte Caves (of which I am a member) and I’m hoping we can get someone from a university to pursue an Honour’s project here. Chris isn’t going to be able to come back to the US with me when I leave, so there’s a possibility that he could take up the work for his Honour’s project. For now, Mick Dennis has said he’d like to learn how to operate the cameras and analyze the counts, so at least he’ll be able to continue the project in the short-term after I leave.

 The entrance to one of the caves was full of blackberry bushes. Ouch!

 

Mick using a thermal imaging camera to look for bats in the cave while I record information.

A large cluster of bats in one of the caves we surveyed.

 This was how I counted the bats in the photos. I used the program Paint to put marks on each bat as I counted it. It took awhile to go through over 5000 bats!

Another exciting thing that’s happened here is the installation of the new fence around Bat Cave. In one of my previous posts ("Stepping in to Help the Bats") I explained that when the pups started flying in the summer, the number of hits on the fence increased dramatically. In order to minimize the number of hits, we decided to move the fence back several meters from the cave entrance, which would hopefully give the bats, especially the pups, more time to see and avoid the fence. After many conversations and modifications to the new fence design, we finally installed it in early June. Three of the sides were moved back about 3 meters, and the front was moved back about 10 meters. Now when I set up both thermal imaging cameras (the one near the cave entrance and the one far from it) I don’t have to take down the whole front of the fence so it’s not in the camera view. We are also planning to build a permanent shelter in which the thermal cameras can be set up and run, even during inclement weather. I’m not sure if that will get done before I leave, but it’s on the agenda to do.

In other bat-related news, I was contacted by Stuart Stansfield from the ABC SE Breakfast program (on the radio) to do another interview about my work with the bats. Of course he wanted to do the interview in the middle of when I was sick with a cold, so I didn't sound my best, but it did go well. You can listen to the interview below.