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Jane Edmanson OAM
ABN:53 715 421 623
Why have bat boxes in the Melton Botanic Garden?
Australia has been divided into bioregions by scientists to define areas that have bat habitats and species groups that are unique to others in any particular landmass.
Melton is part of the Great Dividing Range bioregion. The Great Dividing bioregion stretches from Cape York Peninsula along the coast to just over the Victoria/South Australia border and includes Tasmania. This is one of Australia’s most diverse. The east coast is the only part of Australia where all of our 8 bat families are represented. There are 52 species in this bioregion. This area includes a huge variety of bat habitats. The variety includes; habitats that are in original condition to others that have been severely changed by agriculture and urban growth, climate variations from tropical to cool and the ecosystems from dense forests to open woodlands and grasslands. Some species of bats in this bioregion cover extensive areas others are just in small unique pockets.
What micro bats can be found in Melbourne?
Micro bats found in Melbourne are: Tiny Vespadeluses, the Large, Southern and Little Forrest Bats, the Inland Broad-nosed bat, Eastern Broad-nosed bat, Lesser Long Eared, Gould Long Eared, Large-footed Myotis, White-striped Free-Tail, Very rare Yellow-bellied Sheath-tailed Bat.
Surprisingly cities and town have lots of bats. They are easier to find at nights when they are feeding than during the day when they are hiding. They can be found near street lights that are near water such as ponds, creeks and lakes because of insects. Areas in cities that have trees and the magic element water, that ensures and abundant insect supply, are great natural resource for micro bats.
Some interesting facts about bats
- 35 species of micro bats are threatened species.
- A small insectivorous bat can have a heart rate of up to 800 beats per minute when flying.
- During winter torpor, Eastern Bentwing Bats drop their heart rate to approximately 30 beats per minute.
- Bats nearly always travel in a forward or sideways direction when crawling.
- When their wings are folded closed many bats use their wrists and thumb claws as front legs during the quadrupedal locomotion on the ground and vertical surfaces.
- They also use their coats as wrap-around raincoats, as a blanket to keep newborn young warm, as fans for temperature control and during threat behaviour.
- Bats are good swimmers and use their folded wings in a rowing motion to travel across the surface of water.
- The wing membrane of bats is composed of a double layer of almost hairless epidermis (surface skin) with a thin layer of connective tissue between. The connective tissue layer contains blood vessels, nerves, slips of skeletal muscle (plagiopatagiales muscle) and a criss-cross network of elastin fibres.
- For Bats to be aerodynamically efficient, the wing membranes must be moderately rigid when fully spread. The membrane must be strong enough to resist tearing and flexible enough to fold when the bat is resting. Rips, tears and holes in bat’s wings repair very quickly.
Bats have a greater variety of ear shapes than any other group of mammals in the world. They have long ears, short ears, thick ears, thin ears, pixie ears, pug ears, joined ears and ugly ears. This is more noticeable in the insect-eating bats than fruit bats. Ear shape is an indication of the importance of the bat’s calls, the need to listen to their prey, or unique aspects of their biology such as the way they fly or roost. Their ears are like little satellite dishes that receive their special signals. The change of frequency from a moving object is called a Doppler Shift.
Bat tails and tail membranes (called the uropatagium) are interesting structures and serve many purposes. They can be used in flight as a rudder; they help with the aerodynamic lift required to stay in the air and can also be used as a catching basket for insect prey.
There is a variety of bat noses because the serve different purposes. Some noses are to beam their echolocation call outwards in a precise and direct stream. These bats can aim their calls at a potential prey target, as well guide the returning echoes precisely to their ears without any distortion which may cause confusion. The tube nosed bats have the strangest nose with nostrils that are like forward pointing snorkels, helping them with directional-smelling for fruit dinners. The Flute-nosed Bat has tubular nostrils that point sideways.
Do you know bats can see with sound?
Bats process the echoes of high frequency (ultrasonic) sounds that they make, similar to how a person’s vision processes the wavelengths of colours so that an image is formed. Our brains process light in many millionths of a second, and bat brains do the same with sound echoes, or lack of them. When an insect flies into view a bat quickly notices it, again in a millionth of a second. When cruising around bats are scanning their environment with ultrasonic calls emitted at around 10 calls per second. When they detect a flying insect, to increase their targeting ability they increase the calls to 20 per second. Australian micro bats use echolocate and ultrasound in several ways and with the exception of White-striped Free-tailed bats and Bare-rumped Sheath Tail bats, none can be heard by humans.
When do bats breed?
Bats breeding is geared to the seasons. Whether bats feed on flowers, fruit or insects these resources are best supplied during summer, so bats take advantage of this period of plenty. Most species only give birth to a single young and only breed once a year. There is a typical pattern of young being born in November-December and weaning around the following January-February. The fact that bats do not breed until they are at least 2 years old and there is only one young per mother means it is a low breeding rate for bats.
Bats have their own mother’s groups!
Many bat species form maternity groups, mostly between 10-100 mothers. The advantage of bat maternity groups is the body heat warms up the roost for the young. The disadvantage is that they can attract the attention of predators and parasites.
Maternity sites are important in the life history of bats. Many sites, particularly those in caves, are traditional and have been selected for hundreds if not thousands of years because of special features. These features can be location, reliable local food resources, aspect, micro climate and cave architecture.
Why the variation in what bats eat?
Specialisation has developed in feeding because of their similarity and small body size. This has allowed bats to occupy more feeding sites than most mammalian groups.
Tropical regions provide a diverse range of food types while in the temperate and cooler regions of Australia the majority of bats are insectivorous.
About 55% of bats are insectivorous; some of these are carnivorous as well. The rest eat plant products such as fruit (frugivores), nectar (nectarivores), and foliage (folivores).
Teeth often give a good indication of what food a particular bat eats. Big flat molar teeth are for crushing fruit. Molars with pointed cusps are used to chew the hard bodies of insects such as beetles. Very small or absent molars indicate an almost liquid diet.
Australian Flying Foxes are known to carry pollen over 20km in one night’s feeding. Many of Australia’s forests of hard wood (a wood used in building), only produce fresh pollen and their greatest amount of their nectar at night. The pollination of these important trees is a special role played only by flying foxes in Australian forests. It is amazing to think when these bats pollinate trees that in 40 years or more could be timber in hardware stores.
Bats are a natural pest control
Many of the insects consumed by bats are pest species such as mosquitoes, flies and moths whose grubs damage crops. Each bat consumes roughly 1/3 – 1/2 of its body weight in insects per night, but some lactating females have been recorded eating almost their whole body weight in insects in a night and do so night after night in the two or so months that they are raising their young.
An example of the way a large bat colony can impact on insect population is: It is estimated that a colony of 100,000 Little Bentwing bats (8 grams in weight) at Mt Etna consumes 400kg of beetles, moths and mosquitoes each night. Divide this amount by insect weight this means 4,000,000 insects are consumed every 24 hours.
This shows the importance of bats in reducing pests, which reduces the use of pesticides.
Bats are our unsung heroes of our crops and forests.
Where do bats hang out?
When roosting generally big bats don’t hide but little bats like to hide. Small fruit bats like to hide in foliage and insect bats like to roost where they can be hidden, this can be caves, tree hollows or cracks and fissures in dead tree trunks or under loose flaking bark. They have also adapted to hide in buildings, inside rooves, walls inside farm sheds, sleeping deep in the folds of bags and hanging rain coats. As a way to avoid predators, many species live in small colonies and have a network of roosts in their landscape, and shift around every few days.
Although coastal forests are known as habitats to a high biodiversity of bats open habitats such as woodlands, mallee and even deserts can also support a high biodiversity of bats. To maintain species numbers good levels of understorey and points of water are required.
What reduces bat numbers?
- Bats are eaten by a number of predators, feral cats, foxes, amphibians and birds. Some predators wait until large colonies leave their roost to attack them. Birds attack from behind, when bats are echolocating in the direction they are flying they are unaware if they are being chased from behind.
- Clearing of old-growth trees with tree hollows that take many years to form.
- Bushfires can be devastating for bats because of destruction of habitat and food sources.
- Loss of tree hollows for bats that are known to need small tree hollows, only big enough for them to gain access, for protection against predators, such as goannas, possums, birds and snakes.
- Barbed wire fencing is responsible for the deaths of many bats. This death can be slow and painful and take several days.
- Electrocution on power lines.
- Cocos palm fruit is toxic to bats. It has been declared an obnoxious weed by many councils.
What can we do to help?
- Maintain old trees with single large hollows. These are used by bats as the main roost for breeding and raising their young as well as being a communication centre.
- Maintain woodlands with good understorey.
- Provide bat boxes as extra places for bats to hide during the day. Bat boxes are also used by orchardist to attract colonies of bats to their crops as a way of getting free pest control.
References: Bats Working the Night Shift written by: Greg Richards and Les Hall
For more information:
www.dse.vic.gov.au › Plants & Animals › Flying-foxes
Lumsden: LF & Bennett: AF – 1995 Manual of Victoria