Some people find bats mysterious or even scary. In reality, bats are the most abundant order of mammals in the world after rodents, and many perform important functions as pollinators, seed dispersers and insect controllers in a variety of habitats on all continents except Antarctica. The term ‘meagabat’ is often used to describe fruit bats or flying-foxes, whereas ‘microbat’ refers to other bat species which are generally smaller and eat mostly insects. Until recently, these terms were used to categorise bats belonging to two suborders; Megachiropera (megabats) and Microchiroptera (microbats). Molecular studies have since shown this classification to be incorrect, as the Ghost Bat, leaf-nosed bats and horseshoe bats have been found to be more closely related to flying foxes than they are to other microbats. This group of bats is now referred to as the Yinpterochiroptera, whereas all remaining microbats have been placed in the suborder Yangochiroptera.
While flying-foxes have a diet consisting mostly of fruit and are able to locate their food using sight and smell, most microbats detect their prey through echolocation. Although not blind, echolocation is the primary means by which microbats navigate and locate their food. They do this by creating impulses of sound at high frequencies that are emitted either through the mouth or nostrils. The sound bounces back off objects it encounters and is picked up by the bat’s ears. The information then travels to the brain where it gets processed to give the bat a picture of its surrounding environment.
The White-striped Freetail Bat (Tadarida australis) is one of only two species of microbat in south-eastern Australia with an echolocation call that is audible to the human ear. Many people including those living in inner city areas would have heard the distinctive insect-like call of this species, but may not have recognised it as coming from a bat. These bats mostly fly high above the tree canopy catching moths and other high-flying insects, although are also known to occasionally come to the ground where they forage for ants and flightless beetles. During the day they roost in tree hollows either solitarily or in groups of up to 25 individuals. Although large for a microbat, the White-striped Freetail Bat only grows to about 10 cm long. The common name of ‘freetail bat’ comes from the extension of the tail beyond the end of the tail membrane. The Yellow-bellied Sheathtail Bat (Saccolaimus flaviventris) also has an echolocation call that is audible to the human ear, and is occasionally encountered in the Melbourne area when it migrates into southern Australia over summer. Sick or exhausted individuals sometimes turn up in suburbia, but should not be handled directly as this species is known to carry a form of the rabies-like Bat Lyssavirus.
The Common Bentwing Bat (Miniopterus schreibersii) is the only species of microbat commonly found in the Melbourne area that regularly roosts in old mine shafts and tunnels over winter. Frequent disturbance or visitation to these sites when bats are roosting can result in increased mortality, and is likely to pose a significant threat to this species. The Southern or Large-footed Myotis (Myotis macropus) also makes use of man-made tunnels and culverts, often above or close to water and occasionally in the abandoned nests of fairy martins, although they have also been found roosting in tree hollows. The disproportionately large feet of this species distinguishes it from other Australian microbats. The bats use their feet to catch small fish and aquatic invertebrates which make up the bulk of their diet in southern Australia, periodically swooping down and raking their feet at or just below the water surface. Apart from being Australia’s only fish-eating bat, this species is also unusual in its breeding habits, with dominant males establishing individual territories within the roost and vigorously defending their own harem of females.
With the exception of the two species mentioned above, most species of microbat in the Melbourne area roost mainly in tree hollows. Several species including the White-striped Freetail Bat and Chocolate Wattled Bat (Chalinolobus morio) also make frequent use of nest boxes, and can sometimes be seen exiting boxes in the Wildlife Sanctuary at dusk. The forest bats belonging to the genus Vespadelus also roost in tree hollows and are fast, agile fliers, catching moths and other flying insects from under and amongst the tree canopy. Growing to less than 5 cm long and usually weighing less than 5 g, the Little Forest Bat (Vespadelus vulturnus) is one of the smallest bats in Australia and is so small it can fit inside a matchbox! Most forest bats form single-sex colonies outside the mating period, with females roosting in maternity colonies and males roosting by themselves or in small groups. Young Little Forest Bats are able to fly as soon as they have finished suckling and leave the nest, often following their mothers while foraging.
As their name suggests, the long-eared bats (genus Nyctophilus) have elongated ears, although these are often kept folded back when at rest. Although occasionally encountered in drier forests, Gould’s Long-eared Bat (Nyctophilus gouldi) prefers to inhabit the taller, wet forests to City’s north-east, while the Lesser Long-eared Bat (Nyctophilus geoffroyi) occupies a variety of bushland habitats and is one of the most common species of microbat in suburban Melbourne. These long ears of these bats assist them to navigate and detect prey while echolocating, but are also thought to enable them to passively listen for ‘noisy’ prey such as katydids (arboreal crickets).
The Grey-headed Flying-fox (Pteropus poliocephalus) is the only species of fruit bat residing in Melbourne, with the main camp being at Yarra Bend Park in Fairfield. Numbers of Grey-headed Flying-foxes at the camp can increase to over 50 000 during summer but substantially reduce when most of the bats migrate north along the east coast of Australia over winter. Flying foxes feed mainly on the nectar and blossoms of flowering eucalypts and other native trees, as well as the fruits and flowers of a range of introduced plants including domestic fruit trees. Individuals can travel up to 50 km in search of food each night, although usually remain within 15 km of the camp, and can often be seen flying over Melbourne’s northern suburbs at dusk. The closely related Little Red Flying-fox (Pteropus scapulatus) occasionally turns up in the Melbourne area although it is not a resident and much more commonly encountered north of the divide.
While flying-foxes are sometimes regarded as pests in rural and semi-rural areas due to their habit of raiding orchards, they are nevertheless important for pollinating and dispersing the seeds of a variety of native trees, especially in tropical regions of Australia. Given that Melbourne’s flying-foxes intermix with those from other states, their conservation is of even greater importance for maintaining the national population. Although less noticeable, microbats perform an even greater ecological role in Melbourne’s bushland and suburbs, some capable of eating around half their body weight in insects each night! This makes them extremely effective pest controllers; a service that can be encouraged by installing bat-specific nest boxes to improve the availability of roosting sites.