Microbats

Microbats are small, mainly insectivorous bats which navigate and feed using echolocation. In Australia we have approximately 68 species of microbats, 35 of which are classified as threatened species.

Gould’s Long-eared Bat
(Nyctophilus gouldi)

Greater Broad-nosed Bat
(Scoteanax rueppellii)

Northern Free-tailed Bat
(Mormopterus lumsdenae)

Worldwide, bat numbers are declining drastically due to human activity and habitat destruction.  It is estimated that millions of bats are killed every year by wind turbines.  The blade tips can reach speeds of up to 288km per hour (180mph).  However it is the change in air pressure, known as ‘barotrauma’, which is most deadly.  This phenomenon causes the small blood vessels in the lungs of bats to explode, killing them instantly.

Reasons for population decline in Australia include:

  • habitat destruction
  • bush fires
  • pesticides
  • predators
  • competition for roosting hollows
  • disturbances (including intentional) at caves and other sites
  • persecution driven by fear and ignorance of bats.

Microbats live in a range of habitats including tree hollows, but they can often be found roosting in manmade structures including tunnels, bridges and in the roof cavities of houses. Roost sites are changed often to avoid predation.

Microbats give birth to a single baby (although some species have multiple young) through October to December. Microbat babies can be born weighing up to one third of their mother’s weight. The young are born furless with eyes closed, dependent on their mothers for milk and warmth. When babies become too heavy to be carried, they are left behind in the maternity colony. These colonies can consist of a small number of animals, or even several thousand. By 6-8 weeks the young are fully developed and able to fly and feed themselves. Some microbat species can store viable sperm for many months, and others can hold their pregnancy in limbo for months as well.

Most microbats are insectivorous, feeding on lawn grub moths, weevils, caterpillars, midges, flying termites, mosquitoes and other insects. They can each eat as much as 40% of their own bodyweight in a single night (or several hundred insects per hour). Some species catch insects in their mouths, while others use their tail membrane as a catching basket and then consume their prey – all while still in flight. The Ghost Bat (Macroderma gigas), while no longer classified as a microbat, is a small carnivorous bat which preys on rodents, frogs, birds and other bats. There is even a fish-eating bat that scoops small fish and aquatic insects out of the water with its oversized feet!

Echolocation

Contrary to the myth, microbats are not blind.  However they navigate and feed using echolocation.  This is a highly sophisticated method microbats use to generate information about their surroundings. It is achieved by emitting high frequency sound waves through their mouth and nostrils and listening for the echo bouncing back from surrounding objects. These can be solid objects they are navigating around, or tiny fruit flies they are hunting to eat. The echoes bouncing back can tell the microbat the distance from their prey, the size, shape and even the speed the prey is travelling. The sound waves are beyond human hearing range.

There can be very elaborate facial features on microbats such as noseleafs which direct echolocation calls. It is truly an amazing feature and is the subject of a great deal of study.

Different species have different frequency calls, thus specialised equipment known as bat detectors have been designed to record these calls and identify species.

Torpor

To conserve energy, microbats are capable of lowering their body temperature and metabolic rate. This happens frequently in colder months when food is scarce. This mini hibernation state is known as torpor, an energy-saving mechanism also used by other native species including echidnas, pygmy possums and many other small marsupials. After a sudden cold snap, stranded bats may be found that have gone into torpor overnight. The bats can appear almost lifeless, barely moving and are cold to the touch. It is very detrimental to disturb bats during periods of torpor.