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Bats belong to the order Chiroptera which is divided into two groups; the Microchiroptera (Microbats) and Megachriroptera (Megabats). The megabats consist of the large ‘flying foxes’ which eat fruits, flowers and nectar and roost in large colonies in forest or urban parkland. Microbats are insectiverous (or in one case in Australia carnivorous), small in size, use echolocation for navigation and locating prey and are the most common type in Australia. Go out into your backyard tonight, just after civil sunset, and look up into the sky and you will probably see them foraging.
Microbats are a vital, but often misunderstood, part of our ecology and play an extremely important role in the management of insect pests through predation. These bats roost in tree hollows, under bark, bridges, culverts, buildings, etc., and abandoned mines.
Of the 19 species of bats recorded in the Shoalhaven, four of these are obligate cave dwellers whilst a further five are known to inhabit abandoned mines in NSW, NSW National Parks & Wildlife Service 2001, Strategy for the Conservation of Bats in Derelict Mines. Whilst the term ‘obligate cave dweller’ is used this is something of a misnomer as the bats in all areas utilise abandoned mine workings in the absence of any natural caves in the district.
Bats may use abandoned mines for several purposes:
- Night Roost; as a resting spot or just somewhere to eat or digest a recently caught meal.
- Migratory Roost; a stopover or ‘rallying point’ on a migration route.
- Summer Roost; as the name implies a home for the summer months
- Maternity Roost; used to give birth and rear young during the spring.
- Hibernation Roost; strictly speaking the bats in the Shoalhaven area do not hibernate in the true sense over winter, but will spend periods of time in torpor.
Three species, the Bent-wings and the Eastern Horseshoe form discrete summer and ‘hibernation’ roost populations in the Shoalhaven, which makes them extremely vulnerable to disturbance. This disturbance may take the form of:
- Complete Mine closures for safety reasons.
- Mine collapse from natural causes.
- Inappropriate gating of entrances.
- Bushfires and inappropriately planned hazard reduction burns.
- Human disturbance from people visiting and exploring abandoned mines.
Of these the last is probably of the greatest concern in the Shoalhaven district as our population explodes with the tourist influx over the summer months, and most of our mine workings being easily accessible.
Abandoned mines are Dangerous and should only be entered by experienced and capable parties ! It is extremely important that if you make the decision to enter any abandoned mine workings, you do not DISTURB or ATTEMPT TO TOUCH ANY BATS.
At least one major Migratory Roost has been identified, by myself in the Shoalhaven and obviously its location will not be given on this website. Most of our mining areas contain at least one roost.
Remember that prior to entering the torpor of over wintering bats can store up to 35% of their body weight as fat which is then slowly metabolised during winter. If bats are disturbed during this time they can expend up to 68 days of this stored fat, which equates to roughly one third of their winter reserve ! This is unable to be replaced due to the shortage of suitable prey and they may die. This arousal from torpor can be recognised quite easily as the bats ‘shiver’ before launching into flight from their roosting spot. Continued disturbance can cause a colony to abandon a summer or winter roost with disastrous consequences for the bats. Subsequently mines that are frequently visited have only a few bats in them, whilst the larger colonies occur in the more isolated or dangerous workings.
Bats roost in all of the mining areas which contain tunnels or drives and it is important for the future viability of these populations that disturbances be kept at a minimum. At the very least please observe a no entry policy during the months of April to September in any mine that shows evidence of habitation or where socialisation calls can be heard.
As a footnote to the above the NSW NPWS some time ago deemed that passive audio recording of Bat calls posed a threat under the terms of the Regulations and required anyone using bat recorders to have a Scientific Licence. Now I’m all for the ‘precautionary principle’ when it comes to threatened and vulnerable species, particularly bats ! The Regulations define harm as ‘harm an animal (including an animal of a threatened species, population or ecological community) includes hunt, shoot, poison, net, snare, spear, pursue, capture, trap, injure or kill, but does not include harm by changing the habitat of an animal.’ So how does making a passive recording (Audio or Image in Digital, Magnetic Tape or Film) harm microbats ? Who in heavens name came up with this interpretation of the regulations to include recording as a ‘harmful’ activity ?
On the right is a trace of the call of the Eastern Horseshoe Bat (Rhinolophus megaphyllus). This particular one was recorded at Grassy Gully, in the Morton State Conservation Area, overlooking a creek. Bats forage along creek lines and similar areas where vegetation clutter is minimised, so it’s a good spot to record their activity. The figures on the left give the Frequency in kilo hertz. The range of sounds audible to the human ear is 20 Hz to 20 kHz so we need to use an ultrasonic detector to record sounds like this.
Click on the Icon above to view some Infra Red Video of Bent Wing Bats (Miniopterus schreibersii oceannensis) emerging from a mine in the Shoalhaven District.
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