Recently, while taking overseas relatives on a trip along the Great Ocean Road, I called in at the Cumberland River Cave, located south of Lorne, on Victoria's West Coast. This sea cave was the subject of a previous article in ACKMA Journal (Henderson, 1991).

The cave itself is accessed along a beach, after passing several rocky rises. Its entrance passage is has a diameter of about 1.5 metres, and is, perhaps, 6-8 metres long, leading to a medium-sized chamber. Where the entrance passage (which requires stooping only) meets the chamber, there is a large, active stalactite. It is probably a metre wide and three metres high, and almost reaches the floor. The chamber walls are, in part, covered in flowstone and fluted speleothems, and the cave is the home of a bent-wing bat colony. In my infrequent visits to the cave over the years, bat numbers have seemed to hover at about twenty plus. Up until recently, the cave was not gated. It is well known by locals, with casual visitation, one suspects, to quite frequent.

And so I led my relatives to it ... The first thing I noted was a Parks Victoria sign outside the cave, saying that the cave was closed to protect its bats. My initial reaction was okay, far enough - clearly it's been gated. So, I went to check out the expected gate. No gate at the entrance or near it, though. Curious, I thought. Thus I made my way through the entrance tunnel and into the chamber, to behold - the gate!! Oh yes, it is gated - a very massive grill has been placed right across the entire centre of the chamber. It is roughly 6 - 8 metres wide, and 3 - 4 metres high, with a padlocked door in the steel grill to the right hand side. The gate has a reasonable gap on top (i.e: to does not connect to the cave ceiling), which I thought odd (I was subsequently to discover why)- although one would need to be very energetic to scale it and enter the back of cave.

My initial reaction was one of indignation - what an absurd place to put a gate! Arguably, gating was long overdue, but in the centre of the chamber!!?? Why Parks Victoria didn't put a gate at the entrance area - say half way through the entrance passage, I could not readily fathom. Clearly, an entrance passage gate, to begin with, would have been far cheaper to install. On first view therefore, my quickly-gained opinion was that, from a cave management perspective, I was witnessing a very unfortunate decision, to say the least. I could see three obvious objections:

1. The bats are not protected, as obviously was the aim. One can now still gain access to the middle of the chamber, and can easily shine lights on the bats, yell and scream, and disturb the colony. There is still more than enough room to hold a good-sized party in the cave, outside the gate. The gate, as positioned, is appeared completely superfluous.
2. The main feature of the cave, the large stalactite noted above, is on the wrong side on the gate. Of course, presumably the gating was done just to "protect" the bats, not the cave itself.
3. The sign outside the cave draws attention to it. Again, this to me looked like an awful decision. The cave entrance is relatively concealed, and can only be seen if one is directly opposite it. It would be easy to walk up the beach and miss it. Given the sign, it is now impossible to miss!! Why on earth the sign was not put inside the cave, say on the wall near the gate, or better still on the gate itself, I could not comprehend.

These were my perceptions. I suggest that anyone else with some cave management knowledge and confronted with the above, would probably reach similar conclusions to myself. If nothing else, I wanted some answers.

After my trip, I advised Elery Hamilton-Smith of the situation, about which he had no information. He did comment though, that bent-wing bats do not like gates. He then put me in contact with the bat expert from the Department of Natural Resources and Environment, Lindy Lumsden, who responded as follows:

"The local Parks Victoria people have been concerned for some years that the high level of visitation to the cave was impacting on the bat population. The species using the cave is the Common Bent-wing Bat that is listed as vulnerable in Victoria. They asked for my advice on ways to protect the bats. Over the last few years I have been experimenting with gate designs for caves and mines that would exclude people but allow ready access to bats.

"Unfortunately, the Common Bent-wing Bat does not accept the standard bat gate design used for other species. The standard design has horizontal bars with 15 to 18 cm gaps between them. I tried this design in a mine used by bent-wing bats several years ago, and almost the entire colony of approximately 1000 animals deserted the site. They re-colonised it again once I had opened the gate. Watching their behaviour on an infrared video camera it was apparent that they were physically capable of flying through the gap between the bars, but extremely reluctant to do so, circling up to 60 times in front of the gate before 'plucking up the courage' to fly through. Once they had flown through they did not return to the mine until the gate was removed. I experimented with various gap dimensions, types of bars etc. and had to increase the gap to 30 cm before they did not desert the site (although they still circled numerous times before flying though). A gap of 30 cm is, of course, no barrier to people so this is not a suitable option for a gate.

"In the Cumberland Cave the exit passage past the stalactite is already fairly confined, and in my opinion, any barrier in this area would result in the bats deserting the cave totally. Therefore, I recommended against installing a gate in this section. The other possible options were to put a fence on the beach around the outside of the cave, or a barrier inside the cave. The fence option was not considered feasible due to the distance away from the opening it would need to be to allow the bats sufficient open flight space, the logistics of setting it on the beach, the difficulty in maintenance and the attention it would draw to the cave.

"The other possible option was a barrier inside the cave. As the bats will not fly through bars, the barrier had to work like a fence rather than a complete gate, enabling the bats to fly freely over the top. Therefore, the plan was to insert the barrier inside the cave just far enough in to allow the bats space to fly down from the top of the chamber, over the top of it and into the passage to the outside. It was recognised that this would not offer the bats as much protection as if people were excluded totally from the cave, but that it could be of some benefit. I recommended that information should be attached to the barrier to inform people of why it was installed and the importance of not disturbing the bats. This, combined with the fact that if people were able to enter part way into the cave and so feel that they had had a 'cave experience', they would then hopefully be less inclined to try and climb over the barrier.

"While some people would still make noise and shine lights around, it was felt that this level of disturbance would be reduced compared to what would happen if they had full access to the cave. The greatest effect on bats occurs if people get too close to them, especially if they are touched or handled. It is especially important that the level of disturbance is minimised over winter when the bats are inactive and reduce their body temperature to conserve fat reserves. While I could not guarantee that installing the barrier inside the cave would reduce disturbance levels to the bats, we all felt that it was worth a try, and that future monitoring would determine if it was successful. The barrier had to be constructed within the cave, and we did not want the bats to be present while this was done, so they were excluded during the two days of construction. The bats returned to the cave within a couple of days. Since then approximately fifty bats have regularly used the cave. Prior to the installation of the barrier the numbers were often lower, especially during school holidays when disturbance levels were highest and often only very small numbers of bats remained. The monitoring program is continuing."

As can now been seen, my perceptions from a cave management perspective, while arguably sound in themselves, needed considerable adjustment when taking into account the "bat equation". As Lindy has explained, protecting the relevant bat species, given its hatred of gates, is a vexing management problem with no easy solution. Clearly, in this case, cave management and bat management are not happy bedfellows - although one could immediate state that, generally-speaking, bats are considerably more liable to extinction than caves.

Lindy does make a very good case, against what I had initially perceived to be fairly appalling decisions from a cave management viewpoint - which they remain if viewed only from that perspective. Of course, from a bat management point of view, it is a quite different story. One hopes that the errors in the original project - the sighting of the sign, and perhaps the exact positioning of the gate in the cave, will be addressed, particularly the former.

That said, I must say, I am still disposed to lean somewhat towards "Point One" of my initial criticism above. Given that any who wishes to can still readily disturb the bats anyway with the gate, as positioned, in situ - I am still a bit inclined to believe that this gating may yet prove superfluous, and that no gate, with just appropriate internal signage in its place, might be the best way to go. The results of the ongoing monitoring should give us a clearer picture, in due course ...

Reference

Henderson, K. (1991). An Interesting Little Sea Cave. ACKMA Journal No. 7.