Each year in early spring (around September), thousands of pregnant females return from their wintering caves across south-eastern Australia to the ‘Bat Cave’. In early summer, the female gives birth to a single offspring called a pup, although there are records of twins being born. The pups are born without fur clinging to their mother for the first few hours before being placed in an aven (domes in the cave roof) that serves as a nursery.

With temperatures of over 30°C, the ‘maternity’ chamber provides the perfect environment for the nursery. The heat is generated mostly by composting bat guano and the bats’ own body heat. The pups are able to fly at about five weeks old, practising their flying inside the cave for several weeks before flying outside to feed on insects.

As the season change and it becomes cool, the bats fly back to their wintering caves where they spend most of the time in torpor. Although other species of bats have been recorded in the area and in the caves, most are Bent-wing.

Bat Cave Teleview Centre
• At Naracoorte Caves there is an innovative viewing centre from where it is possible to view the bats’ daily activities via television monitors. Currently there are five infra-red cameras installed in the Bat Cave, relaying images back to the Bat Cave Teleview Centre, allowing researchers and park visitors to see just what goes on inside the cave. This world-first technology has allowed visitors to witness bats giving birth, feeding their young and the tiny pups develop from a tiny furless ‘jellybean’ to a adult-size flying bat.

Cave Invertebrates
• The Bat Cave has a diverse ecosystem of invertebrates living on and in the huge deposits of guano. Over forty species have been identified including several that are endemic to Naracoorte. One of these species is the Pseudoscorpion Pseudochelifer naracoortensis, a minute predator of other cave dwelling invertebrates.

Around many of the cave entrances, Cave Crickets (or wetas) Novatettix naracoortensis can be seen. These small insects hide in the twilight zone of a cave and only leave at night to feed on rotting vegetation.
 

Naracoorte Caves NP © N Birks

Cave crickets © Naracoorte Caves NP

Tiny Pseudoscorpions
Naracoorte Caves NP © K Sanderson

• Insect eating bats and can eat up to ½ their body weight per night.
• Bent-wing bats weigh 12-15g, therefore could eat 7-8g per night.
• Some bats give birth to twins, but bent-wing bats only have one baby per year, although there have been recorded instances of bent-wing bats with twins. They are usually born in late November-early December.
• Bent-wing bats have developed a very clever strategy of breeding to ensure the baby bats are strong enough to survive their first winter. The bats mate in May, before they go into torpor. There is a delayed implantation of the embryo. The embryo is then dormant for several weeks. It only stats to develop when the bats begin feeding from September onwards. By doing this it allows the baby bat maximum time to grow and store enough body fat to survive the first winter.
• The bat cave temperature rises to above 30°C at the roof. The cave is heated mainly through the guano piles composting. Minor temperature fluctuations maybe due to the bats body heat and the very thin roof of the cave which may allow some solar heating but also a means for heat to escape.
• The caves bats use for seeing out the winter are cold as this helps the bats slow down their metabolism and lapse into torpor. The bats generally congregate in torpor in the twilight zone of the cave. This is generally the coolest part of the cave and also it is possible that they use this part of the cave so they can see the weather outside. If it were raining outside the bat would not have to warm its body up to flying temperature hence wasting energy to go out and have a look.
• Waking up out of torpor involves a large expenditure of energy. The bat actually burns its fat reserves to warm up its body. This is visible as while this is happening the bat shakes and this gives the appearance of being nervous. The bats can’t fly without warming their body up and if
  disturbed can drop from the roof.
• Blanche cave can go down to as low as 9°C in winter.
• Albino bat recorded in the cave in 1999
• The dates that the pups have been first seen in the four years the cameras have been in:
  • 1995 Dec 12
  • 1996 Dec13
  • 1997 Dec 14
  • 1998 Dec 3
• For the first few days of life the baby bats cling to their mother, even while she is flying around the cave. After a few days the pups are placed in the nursery, which then allows the mother to leave the cave to feed.
• Pups born with large feet which allow them to hang on.
• Bent-wing bats are fast fliers – not as manoeuvrable as some. Eg. Small forest bats are “gleaners” and feed in and around trees, while bent-wing bats generally feed over open water or across the top of the trees.
• Their feet have locking tendons which is why they don’t fall from the roof when they are asleep and even after they die hanging on to the roof.
• Bent-wing bats can fly 50 km+ per hour.
• They can fly up to 50 km away from the cave at night – at Naracoorte there is plenty of food close by eg. Bool Lagoon so they may not venture such large distances.
• They can travel up to 200 km to wintering caves.
• Dangers for the bats:
  • Summer - Owls, Disturbance by humans
  • Winter - Disturbance (Woken out of torpor), Winter caves (Fill in, Gated – can’t get in, Used for dairy effluent)
• Benefits – eat insects that are pests to agriculture.
• Insect eating bats find their way around using echolocation. This is a series or high pitched sounds emitted by the bat which ‘bounce’ off objects. The bat hears the sound back as an echo. They collect echo via elaborate ears and they distinguish whether the object is food, a wall or a potential predator.
• Bent-wing bats have been reported at greater that 30 years old through a banding program.
• Commonly have ectoparasites (Bat flies which are conspicuous by their orange colour).
• Egg for fertilisation always from the left ovum.
• Reach sexual maturity in 2nd year of life.

Other bat species in the region are: