There are many excellent sources of information available about bats, however the following is a brief introduction to their special characteristics.
Bats as we recognise them today have been on earth for at least 55 million years. Their evolutionary origins are a subject of debate as fossil records are rare due to their delicate bone structures.
Bats are the only mammals capable of sustained flight and are perfectly adapted to achieve this. Bats belong to the order Chiroptera (meaning 'hand winged') and are divided into two suborders, Microchiroptera and Megachiroptera:
These are small, mainly insectivorous bats which navigate and feed using echolocation. It is believed that microbats evolved from a shrew-like ancestor being born blind and without fur.
In Australia we have approximately 63 species of microbats that live in a range of habitats including tree hollows, caves, roofs and wall cavities of houses, and change roost sites often to avoid predation.
Microbats give birth to a single young (some species have multiple young) through October to December. Microbat babies can be born up to one third of their mother's weight, so when they 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.
Left: a Microbat
Microbats could be considered nature's can of Mortein as they can consume thousands of insects in one night. The smallest microbat is the bumble bee bat from Thailand weighing only 1.5gms.
Although most microbats are insectivores, there are also some carnivorous species. Some larger species prey on smaller species and there is even a fish-eating bat that scoops small fish out of the water with its oversized feet!
Microbats have a unique way of conserving the energy they need to sustain flight while feeding and echolocating. They are capable of going into what is called 'torpor' by lowering their body temperature which in turn lowers their breathing and heart rate. They can appear almost lifeless as they barely move and are cold to the touch. This happens frequently in colder months when food is scarce.
The system known as echolocation 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. It is difficult to imagine how microbat brains interpret this information to form a perfect picture of their environment. For example, the echoes bouncing back can tell them the distance from their prey, the size, shape and even the speed it is travelling! The sound waves need to be high frequency to get the detail back they require, so is above our hearing range. There are some very elaborate facial features on microbats such as noseleafs that direct echolocations 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.
- illustration © Louise Saunders