Chasing Bat Calls on the Nullarbor

Chalinolobus gouldii — Gould’s wattled bat
Chalinolobus gouldii — Gould’s wattled bat

CLARE BUSWELL FUSSI | Insectivorous bat occurrence data from the Nullarbor bioregion are scant and largely based on capture records or observations in caves.

Currently eight species have been recorded (Table 1) (McKenzie and Robinson 1987; Kemper et al. in prep).

Many of these records were collected from the treed section of the Nullarbor Plain around Balladonia, Cocklebiddy, Madura and Eucla. An additional three species (asterisked in Table 1) are known from the fringes of the Nullarbor Plain proper (Kemper et al. in prep).

Of these 11 species, only Taphozous hilli and Chalinolobus morio are known as natural cave dwellers. There is only one old record of T. hilli from the Nullarbor, taken from a cave near Ooldea (Jones 1925).

Chalinolobus morio — Chocolate wattled bat
Chalinolobus morio — Chocolate wattled bat

The whereabouts of this specimen is unknown but the description is unequivocally a Taphozous, and there is no obvious reason to doubt its provenance. T. hilli occurs across middle Australia but the nearest record to Oldea is over 400 km to the north east.

C. morio is also a widespread species across southern Australia (Churchill 2008) and apart from caves on the Nullarbor Plain, Eyre Peninsula and Kangaroo Island in SA, it naturally roosts and breeds in tree hollows. Some caves on the Nullarbor are well known maternity caves with some colony sizes in the order of 5000 individuals (Hall 1971).

Listen to the calls of Chalinolobus morio below.



Mummified remains of Nictophilus geoffroyi have been recorded from near Oasis Lakes in Mullamullang Cave and there are records of dead individuals of Chalinolobus gouldii over 1km into Mullamullang Cave.

Nyctophilus species remains have been found in the doline of Warbla Cave. None of these species is thought to be regularly using the dark zone of Nullarbor caves as natural roosts or breeding, and along with Scotorepens balstoni, Mormopterus species and Vespadelus species, usually roost in tree hollows.

Bat detector
Bat detector

The aridity and treelessness of the Nullarbor Plain probably form a biogeographic barrier for east-west movement of tree-roosting bat species, but the lack of survey effort is certainly responsible for our incomplete understanding of the extent of occurrence of some species.

The use of bat detectors to remotely record and identify the echolocation calls from bats in flight has greatly enhanced bat survey efficiency. This has prompted us to take the opportunity during Nullarbor cave expeditions to record bat calls from cave entrances and nearby habitats, thus adding to the existing knowledge of bat occurrence.

Table 1: Identified bat species on the Nullarbor Plain, by Family, Scientific and Common Names.

Family Scientific name Common name
Emballonuridae Taphozous hilli Hill’s sheath-tailed bat
Molossidae Austronomus australis White-striped free-tailed bat
Mormopterus sp3 Inland free-tailed bat
Mormopterus planiceps* Southern free-tailed bat (east)
Vespertilionidae Chalinolobus gouldii Gould’s wattled bat
Chalinolobus morio Chocolate wattled bat
Nyctophilus geoffroyi Lesser long-eared bat
Nyctophilus major Central greater long-eared bat
Scotorepens balstoni Western broad-nosed bat
Vespadelus regulus Southern forest bat
Vespadelus baverstocki Inland forest bat

Method and Results

The project took place over two years in September 2011 and 2012, and the area covered was divided into two sections that corresponded to two different ecosystems.

Although they are both in arid areas, Area 1 consisted of the woodland habitat south of the Dingo Fence and Area 2 the truly treeless region around Old Homestead Cave.

Essentially the area ranged from Eucla to 40km south of the railway line and as far west as Mullamullang Cave on the Western Australian side of the Plain.

We had designated 13 sites, eight in area 1 and five in area 2. We used four Anabat bat detectors and were expecting to record approximately 13 hours of data per night x 13 nights for each detector for the first year with similar recording time for the second year of the project.

Our recording plan was to put out two detectors on the edge of dolines, a third around 500m from the doline and the fourth detector was to be used on a transect near cave entrances. Recording would start at dusk and end at 8am each morning.

Fieldwork 2011

The Nullarbor in September of 2011 showed a landscape of abundance. Grasses were thick and tall, dolines were full of wildlife: owls, kestrels, swallows, budgerigars, feral cats, rabbits and foxes. Cave floors were wet; some showed evidence of such recent water flows that all indications that cavers had ever visited were gone.

Indeed, the rainfall on the Nullarbor in 2011 was double its normal level, with Mundrabilla Station receiving 400mm of rain up until mid-September.[1. Mundrabilla Station owner pers. comm. See also Bureau of Meterology: Eucla weather station, number 11003, commenced operations in 1876. Mundrabilla weather station, number 011008, opened in 1901.
http://www.bom.gov.au/climate/current/statements/scs38.pdf]

[pullquote]After about an hour of this blissful calm all hell broke loose with a storm that threatened to blow most of our camp back to Eucla. The temperature dropped 5ºC in an hour[/pullquote]The first site in Area 1, Weebubbie Cave, has a known bat maternity site. We arrived at Weebubbie on Sunday 18 September around dusk, to a warm (28ºC at 7pm) evening.

We put out two detectors and then set up camp. After about an hour of this blissful calm all hell broke loose with a storm that threatened to blow most of our camp back to Eucla. The temperature dropped 5ºC in an hour. We retrieved both bat detectors and bunkered down for the night. The storm reportedly tore roofs from houses at Kalgoorlie. The upshot of this was that no data were recorded for the hour the detectors were out.

The next site was in Area 2, at Old Homestead Cave. We recorded data here for five nights. The detectors were put out around 6pm and retrieved around 8am the following morning. The nights were cold, 8ºC; days warm to hot. The wind sprang up most evenings, starting around 6pm and tailing off around 8-8.30pm; this dropped temperatures considerably.

The position of the recorders remained the same during this period, with detectors facing into both the southern and northern dolines. Each morning we had a computer and voltmeter session. We would download the data, check battery levels and make sure that all equipment was in working order.

We recorded no bat calls at this site. Other wildlife was in abundance, however: nesting pairs of kestrels, owls, swallows, ravens and a feral cat with kittens, all living in the two Old Homestead dolines.

Webbs Cave was the next site. This cave is a known bat maternity site and is in the woodland of Area 1. We recorded here from the evenings of 26-28 September.

We put out three detectors, one high up on the doline edge, one at 100m from the south-western side of the doline and the third 900m due west from the cave. We recorded three calls of C. morio at the edge of the doline on the night of the 26th, and nothing 100m back from the cave or 900m from the cave.

Then on the evenings of the 27th and 28th 10 calls were recorded 900m from the cave. These latter calls consisted of nine C. morio calls and one C. gouldii call. No calls were recorded at the doline on the 27th or 28th. The nights here were warmer, around 12ºC, than those at Old Homestead, and the wind was not an issue.

We then moved to site 3 in Area 1, the Mullamullang doline, arriving late in the evening of 29 September, and placed one detector facing into the southern doline. The night of our arrival was cold, getting down to 6ºC at 6am, with a sharp wind from the south.

Despite this, we recorded more than 278 calls.

For the next two nights we recorded over three sites.

Two of these were at the doline itself, with two detectors facing into both the northern and southern dolines. A third detector was placed at the usual campsite about 400m from the doline. The calls recorded below came from both the northern and southern dolines with nothing recorded at the old campsite for any of the nights we collected the data. Calls are summarised at half-hourly intervals.

bat-graph-1

The above graph shows considerable activity for the Thursday evening, despite the cold and wind throughout the night. There were 278 calls from Chalinolobus morio and 24 calls from C. gouldii.

bat-graph-2

There was a total of 495 calls from Chalinolobus morio, four calls that were not identified at 44-45kHz, and eight calls from Mormopterus/ C. gouldii.

The data for the northern doline of Mullamullang, which is the doline that opens up into the major cave, showed a total of 510 calls: 478 calls from C. morio, 14 calls from Vespadelus and 18 calls from C. gouldii on the one night that we recorded from this doline. On the graph the latter two species are shown as “Other”.

bat-graph-3

As the graph shows, most of the activity occurs around 8pm, with 221 calls being recorded, and a second peak at 1am, with 24 calls recorded. All three graphs show this pattern of two activity peaks during the course of a night, as bats tend to go out to feed a couple of times a night. Below are samples of the calls recorded in 2011.

bat-graph-4

Fieldwork 2012

To obtain some sort of consistency in sample selections we tried to be at the same cave sites on the same day as on the previous year, although our trip was not as long or as extensive.

Sampling took place in both areas, but with only two sites, that of Webbs Cave in Area 1 and Old Homestead in Area 2. We particularly wanted to resample Webbs Cave due to the lack of data collected in the area in 2011, so it formed a high priority on this trip. Once again no calls were recorded at Old Homestead Cave over the three nights of recordings.

bat-graph-5

At the doline sites of Webbs Cave, over the two nights of sampling, a total of 726 calls, all from C. morio, were recorded. We placed the detector on the western side of the doline in the same place as the previous year and on the same night exactly one year apart — 28 September.

bat-graph-6

On the evening of 29 September we recorded a similar number of calls, with a noticeable second feeding spike (32 calls detected) at 1.30am. The data collected here are more consistent with its known role as a maternity site.

Conclusions

The Nullarbor in September of 2011 was lush. All the dolines we entered or looked at contained abundant wildlife.

Baiting for wild dogs had occurred as far north as the railway line and the Calicivirus was also doing damage to the plagues of rabbits that could be seen along the way.

The landscape itself consisted of tall grasses, as well as the usual bluebush and saltbush.

The abundance of vegetation was consistent from the highway to the railway line. The tall dry grasses posed a real fire hazard and indeed it set our car alight on the way to Mullamullang Cave. DOLA was attempting burnoffs north of Mundrabilla station along the road to Forrest in an attempt to control fires started by lightning strikes.

As a result smoke was sometimes smelt underground and seen above it. Fire hazards, storms and breakdowns made travel difficult, contributing significantly to our ability to reach sample sites and collect the data expected. In contrast, the Nullarbor in 2012 was back to the more normal dry seasonal landscape.

Of the bat calls identified over the course of both the 2011 and 2012 fieldwork, the majority were from previously recorded species, C. morio and C. gouldii. Bats were observed in Weebubbie, Abrakurrie, Witches, Mullamullang and Webbs caves. They were not observed in Old Homestead Cave. The absence of bats in Old Homestead Cave would seem to confirm the theory that the truly treeless section of the Nullarbor forms a barrier to the movement of bat species northwards from the treed areas of the plain. Bats were not observed in Thampana or Purple Gorringe caves on the days we visited.

Bat detection work on the Nullarbor, despite the travel difficulties, is rewarding and we have collected a reasonable data set, adding to the existing knowledge base. To be consistent, of course, and to undertake longitudinal studies, requires far more input than four bat detectors.

Mist netting would add to the accuracy of the data we collected as it enables identification of species by sight. Placing radio frequency transmitters on bats, as has occurred at Naracoorte Caves National Park, would allow us to track flight paths and find out just where bats are going at night.

As for the thousands of caves on the Nullarbor, we have little to no data on bat visitation to or habitation within.

There is a need, given the lack of long term data and the decline in bat populations generally, to try to establish consistent bat population data, at the very least for the known bat maternity sites of, for example, Weebubbie and Webbs caves. Such research would certainly build the existing data set.

The next time you are out on the Nullarbor Plain over the spring months, take a bat detector with you and help build on what we think we know. Just note, however, that you must have a permit to collect and catch any specimens.

All the bat call data we collected are held by the South Australian Museum.

ACKNOWLEDGMENTS

I would like to thank my fellow trip members, Heiko Maurer, Thomas Varga, Michael Meynell-James and Richard Boyle for their help in putting out bat detectors, downloading data and dealing with the associated issues.

I would also like to thank Dr Ken Sanderson, Adjunct Lecturer, Biology Department, Flinders University, for identifying the bat call data. Our thanks go to both the South Australian Museum and the Department of Environment and Heritage for supplying bat detectors.

Thanks must go to Terry Reardon from the South Australian Museum for his enthusiasm, time and technical support for this project.

We also thank the ASF’s Cave and Karst Research Commission for a grant to help cover some of the costs of the project.

Finally, I would like to thank the owners of both Mundrabilla and Mullamullang stations for granting access to their land, without which this research would not have been possible.

REFERENCES

Churchill, S. 2008 Australian Bats. (2nd ed.) Allen and Unwin. Sydney.

Hall, Leslie S. 1971 A Collection of the Bat, Chalinolobus morio (Gray), From The Nullarbor Plain, Western Australia. Helictite, 8(3): 51-57.

Jones F. W. 1925 The Mammals of South Australia. Part III Government Printer. Adelaide. pp. 271-45

Kemper, C., Stemmer, D., Reardon, T., Medlin, G. and Shaughnessy P. (in prep). ‘Mammals’ [in] Census of South Australian Vertebrates 4th Edition. Department of Environment, Water and Natural Resources.

McKenzie, N. L. & Robinson, A. C. 1987 A Biological Survey of the Nullarbor Region South and Western Australia in 1984. Government Printer. Adelaide.

National Climate Centre, Bureau of Meteorology 2012. ‘Australia’s wettest two-year period on record; 2011-2012.’ Special Climate Statement 38.