Before focusing on the ghost bat, let’s take a quick look at bats in general throughout Australia.
Bats are marsupial – the only ones with wings. Australia is home to over 90 species of bats which range in size from the fruit bat (1 kg and 1.5 m wingspan) to the insectivorous bats (3 g and can fit in a matchbox). Bats are the second largest order of mammals – with over 1,400 species worldwide, they account for about 20% of all mammals. Unfortunately for bats, they are misunderstood and therefore feared – considered dirty and dangerous. Worse still – they are generally nocturnal.
Let’s get the “dangerous” bit out of the way first. Australian bats can carry lyssavirus, which is closely related to rabies – usually fatal in both cases. This virus is spread through bites and scratches. But since this virus was first identified in 1996, there have only been 4 cases identified in Australia, so it is not a major risk.
Even though bats operate at night, they do have eyes and can see quite well.
The ghost bat is endemic to Australia. It is characterised by the pale colour of the wing membrane and skin with a prominent nose-leaf and elongated ears. It is our only carnivorous bat – it eats large insects, small lizards, frogs, small birds and other bats. It is usually considered to be Australia’s iconic bat. Generally, they are 10 to 13 cm in body length and weigh 130 to 170 g. Ghost bats are important in the control of rodents, especially introduced house mice, and other small mammals.
Unfortunately, ghost bats and mining are closely linked because these bats tend to roost in abandoned mines and caves. Their habitat stretches right across northern Australia – importantly in the Pilbara where they are often associated with geological formations that coincide with iron ore mining. They are also associated with limestone mining in Queensland.
Even if mining does not directly impact, nearby blasting associated with mine construction and operation can disrupt roosting bats. The creation of the pits, waste rock dumps, roads, leach pads, and processing areas destroys critical foraging habitat and changes drainage patterns.
Ghost bats are vulnerable to several anthropogenic hazards – including barbed wire fencing which they seem unable to detect when in flight and foraging near ground level. Interestingly, wind turbines kill far more bats than birds (that get all the attention) – it has been estimated that millions of bats die each year after slamming into their giant blades. Also, studies have shown that ghost bats will abandon their babies if their roosting sites are disturbed.
Protecting ghost bats through monitoring programs:
Where and when to monitor:
- For baseline impact, gather several nights of acoustic data before noisy activities commence and continue during and after to quantify changes.
- Position monitors at or near known roost entrances, cave mouths and where foraging occurs.
- Concentrate recording from dusk to dawn and before/after noisy activities to capture baseline impact.
Metrics to report:
- Band limited Leq/Leq night for the bands 1-10 kHz, 10-30 kHz, and 30-80 kHz.
- Sound Exposure Level (SEL) and peak Sound Pressure Level (SPL) per impulsive event (blasts, pile driving), plus spectral content of events. Impulsive events can have outsized impacts.
- Bat activity indices (a metric used to measure and compare the relative level of bat activity in an area, often through acoustic surveys that record echolocation calls).
- Collecting this data will require ultrasonic capable systems with a frequency response to at least 100 kHz.
Practical mitigation suggestions:
- Avoid high noise at dawn and dusk and during core foraging periods – i.e. schedule the loudest works for daytime.
- Control low-frequency energy – mufflers, enclosures, noise barriers. Even low-frequency noise can change bat behaviour.
- Minimise noisy events near roosts.
- If monitoring shows reduced activity near works, tighten controls – e.g. lower allowed levels, increase buffer distance.
For further information, contact Texcel about your specific requirements.