Environment Australia, 1999
ISBN 0 642 2546 363
Taxon summary: Southern Bent-wing Bat
Scientific Name: Miniopterus schreibersii (Kuhl, 1819) (Southern form)
Common Name: Southern Bent-wing Bat
Conservation Status: Lower Risk (conservation dependent)
Past range and abundance
This form, which occurs in eastern South Australia and western Victoria, is considered separately from Miniopterus schreibersii oceanensis (refer Taxonomy section).
In South Australia, the Southern Bent-wing Bat has been recorded from Melrose (Flinders Ranges), Mount Lofty and Port Adelaide, Brentwood (Yorke Peninsula) and the far south-east from Naracoorte to the lower Glenelg River. They were considered to be ‘by no means uncommon’ in South Australia by Wood Jones (1925), although this comment was almost certainly referring to the abundance in the south east of the state. The records from the northern areas are few, with some proving difficult to verify. It is doubtful whether the natural distribution of Southern Bent-wing Bat extended very far north of Naracoorte. In south-east SA, the population is centred upon Naracoorte Bat Cave, the major maternity cave for this form. Well over twenty caves in the region have been identified as wintering caves (Hamilton-Smith 1972).
The past distribution of this form in Victoria was based around the cave systems in the south-west of the state. An immense maternity site recorded at Mt. Widderin Cave near Skipton in 1866 disappeared soon after discovery (Simpson and Smith 1964, Hamilton-Smith 1968). Thunder Point Blowhole, at Warrnambool, was used as a maternity site until its partial collapse in the last couple of years. Lake Gillear Guano Cave, also near Warrnambool, is currently used as a maternity site but its former status is unclear – in the past it may have served mainly as a temporary or transient site.
Current range and abundance
In South Australia, the range and abundance does not appear to have changed in the southern part of its range. However, there have been no records in the last 30 years of the species from north of the Naracoorte region. The number of bats currently using the Naracoorte Bat Cave (100,000–200,000 in December) is similar to estimates from the 1960s. This colony is protected by reservation and managed by the South Australian National Parks and Wildlife Service. This reservation has been put in place to manage cave visitation, without which the maternity site would be at risk. Other wintering and staging caves have come under increasing pressure through recreational caving activities but there is no evidence yet that such activity has resulted in any adverse effects on the bats.
In Victoria, the range and abundance has altered significantly over time, particularly through the loss of the maternity sites at Mt Widderin Cave and Thunder Point Blowhole. The Lake Gillear Guano Cave now appears to be the only maternity site remaining for the Victorian population, and its somewhat limited suitability (artificial roof holes serve to generate powerful drafts) makes the status of the population less secure. The numbers of individuals using Lake Gillear Guano Cave (less than 10,000) is considerably smaller than Naracoorte Bat Cave. Other caves near Warrnambool, along the south coast, and at Portland and Byaduk have been recorded as wintering and staging sites. The eastern limit of the distribution of this form is currently being resolved by genetic studies (B. Cardinal pers. comm.). Individuals located in mines in the Ballarat–Castlemaine area of central Victoria and from sea caves south-west of Geelong are being sampled to determine whether they belong to this form or to M. schreibersii oceanensis (for which the closest maternity roost is Nargun Cave in East Gippsland). If the individuals using mines in central Victoria belong to this form, the distribution is likely to have expanded into this region since European settlement as all known roosts are in man-made structures.
The species is an obligate cave dweller (although some individuals occasionally roost in human constructed tunnels and buildings) and is likely to be dependent for its survival upon the only three known maternity caves (Naracoorte Bat Cave, Lake Gillear Guano Cave and the recently collapsed Thunder Point Blowhole). Every year in spring, adult females accumulate in these caves to give birth and nurse their young. Each cave has structural characteristics which allow heat and humidity to build up so that conditions are suitable for the nursing of young bats. In mid to late summer, the bats begin to disperse to several caves which they will use to over-winter. Banding studies show that individuals can move considerable distances – one female flew from Naracoorte to Wombeyan in New South Wales (a distance of 870km) in a little over two months. Where the age of individuals making these exceptional flights is known, they have each been juveniles. The distribution of the Southern Bent-wing Bat is essentially coastal and its foraging areas are associated with major drainage systems.
The recent partial collapse of Thunder Point Blowhole and its subsequent desertion by bats may have a deleterious effect upon the breeding potential of the Warrnambool region population. The current maternity site at the Lake Gillear Cave receives a relatively high level of human visitation, although the impact of this on the reproductive success of the colony is not known. The human disturbance to wintering bats and the widespread use of pesticides are potential threats, although these threats have not yet been shown to have caused a decline in population sizes.
The future of this taxon is dependent upon the protection of the major maternity caves.
- Current plans to repair the collapse damage in Thunder Point Blowhole and to have the Lake Gillear Guano Cave repaired and placed under the care of Parks, Victoria should be encouraged.
- Develop methods for population monitoring at the maternity sites. Method/s should be non-intrusive and provide annual estimates with defined levels of precision and accuracy. When methods are developed, monitor numbers at the two currently used maternity sites, and undertake regular assessments at Thunder Point Blowhole to monitor any recolonisation of this site subsequent to restoration.
- Re-assess known wintering caves to document:
- current state of preservation;
- land tenure/ownership; and
- land owners attitudes/conditions on cave access.
- Continue education programs for cave visitors to inform them of bat conservation issues, particularly the effect of cave disturbance.
- Complete genetic studies to determine the eastern limits of the distribution of this form.
Baudinette R.V., Wells R.T., Sanderson K.J. and Clark B. 1994. Microclimatic conditions in maternity caves of the bent wing bat, Miniopterus schreibersii: An attempted restoration of a former maternity site. Wildlife Research 21, 607–619.
Cardinal B.R. 1997. Genetic variation and population structure in Miniopterus schreibersii (Chiroptera:Vespertilionidae) from south-eastern Australia. Honours thesis, Deakin University, Geelong, Victoria (unpublished).
Codd J. 1997. Overwintering behavioural strategies and roosting activity budget of the common bent wing bat (Miniopterus schreibersii) at the Naracoorte Caves Conservation Park. Honours thesis, Flinders University, Adelaide.
Dwyer P.D. 1969. Population ranges of Miniopterus schreibersii (Chiroptera) in south-eastern Australia. Australian Journal of Zoology 17, 665–686.
Dwyer P.D. and Hamilton-Smith E. 1965. Breeding cave and maternity colonies of the bent-winged bat in south-eastern Australia. Helictite 4, 3–21.
Hamilton-Smith E. 1968. The Insect Fauna of Mt. Widderin Cave, Skipton, Victoria, Victorian Naturalist 85: 294–6.
Hamilton-Smith E. 1972. The bat population of the Naracoorte caves area. Australian Speleological Federation Biennial Conference Proceedings 8, 66–75.
Simpson K.G. and Smith G.T. 1964. Bat mandible from Mt.Widderin Cave, Skipton. Victorian Naturalist 81, 78–79.
Wilson P. 1982. Metrical variation within and between populations of Miniopterus australis and M. oceanensis (Chiroptera: Vespertilionidae) from southeastern Australia. Honours thesis, University of New South Wales, Sydney.
Wood Jones F. 1925. The Mammals of South Australia Pt III, The Monodelphia. British Science Guild, Adelaide.
Authors for the taxon