Bats at Bushy Park Wetlands

Lindy Lumsden was introduced to us and she gave a very interesting talk and slide presentation on her favourite subject. We then ventured to the adjoining cafe for a delicious roast dinner where we continued to talk about Bats and networked with members of other groups. It was then time to go and inspect the four Bat traps which Parks Victoria Rangers - Craig Lupton and Mick van de Vreede had previously set up nearby at Shepherds Bush. The "harp" bat traps are made of a 4 square metre aluminium frame holding 2 sets of 70 vertical fishing lines set above a cloth trough with a plastic cover. As the lines are very thin some bats don't detect them and fly into the lines. When they fall they slide down a plastic sheet into a cloth bag. It is cleverly designed to hold the bats without harming them.
At 9am Sunday morning I rejoined the group to identify the 23 bats we caught overnight. Identification was done by weighing the species, taking the forearm measurement and looking for other identifying features. We caught 16 Little Forest Bats, 2 Chocolate Wattled Bats, 2 Goulds Wattled Bats, 2 Lesser Long-eared Bats and 1 Large Forest Bat. This was a good result as we caught five of the seven species recorded in the park. The species which feed above the tree canopy are obviously harder to catch.

Species: There are around 1000 species of Bat in the world which belong to two main groups: Megachiropteran (mega) bats, and Microchiropteran (micro) bats. Mega bats or fruit bats, of which there are 200 species, generally live in the tropics where there is a year round supply of fruit, nectar and pollen. Mega bats weigh up to 1kg, have wingspans up to 2 metres and lack tails. Some mega bats are called flying foxes because of their fox-like face. Micro bats have 800 species and use echolocation in search of their insectivorous diet. Australia has 75 bat species, mostly the smaller insect eating micro bat. Victoria has 23 species of bat and all except the Grey-headed Flying fox and Little-red Flying fox are micro bats. A large colony of Grey-headed Flying Foxes has recently moved into the Melbourne Botanical Gardens. The Little-red Flying foxes are found north of the divide around the Goulburn Valley. Bushy Park Wetlands in Glen Waverley has 7 species of insectivorous micro bat.

Bats are Mammals: Bats comprise one-fifth of all the mammals in the world. Like other mammals, they are warm blooded, have fur on their body and give birth to live young. All bats have two feet and each foot has five toes with a strong grasping hooked claw, which enables them to hang upside down. It is a misconception that bats are blind, however micro bats don't have such developed senses of sight and smell as do their cousins the mega bats. Bats are generally shy, not aggressive and the only mammals which can fly.

Lesser Long-eared Bat

How they Fly: The unique feature of bats is their wings. The bones of their forearms are the same as other mammals except that they are longer and lighter. The elastic membrane is thin enough to see light through. Bats beat their wings at 15-20 beats per second when they fly. When a bat folds its wings the bones fold like an umbrella; the wing bunches into hundreds of tiny creases. Most micro bats also have a tail membrane between their legs, which they use as a rudder to manouvre in flight and to catch insects in.

Echolocation is a high pitched sound produced in the bat's larynx and directed out through the mouth or nose as short pulses of ultrasonic sound. The sound frequencies range from 11 kHz - just audible to us humans, to 160 kHz. When these pulses strike an object, an echo of the sound returns and is collected by the bat's forward-facing ears. The echoes enable bats to judge the shape, texture and distance of any object such as a tree, building or insects. As the bat gets closer to its prey the frequency increases. With the use of an "anabat" ultrasonic bat detector, these echo location calls can be recorded and the species of bat determined.

Feeding: Being nocturnal, bats are active from dusk to dawn. They are opportunistic feeders and most commonly eat moths, beetles, mosquitoes and other flying insects. Bats can consume up to half their body weight in insects per night. Small insects may be taken directly into the bat's mouth, whilst larger insects are scooped into the bat's wing, transferred to the tail membrane and then eaten.

The Roost: Bats hang upside down attached by their feet, to the ceiling of their home called a roost. The species of bats which inhabit Bushy Park Wetlands shelter by day in old hollow trees or under bark. Individual bats use a number of different roosts, moving between them on a regular basis.

Breeding: Male bats only produce sperm in summer which makes breeding quite complicated, as many bats hibernate over winter. This means techniques such as delayed implantation of embryos or storing of sperm are necessary. In late spring or early summer, one (rarely two) young are born. During birthing, the mother hangs from her roost site by her thumb claws and catches the newborn baby in her tail membrane. Micro bats are born pink, with eyes shut and it is a few weeks before fur covers their back, belly and head. Mega bats are born with fur and open eyes.

A newborn bat's legs are very well developed allowing them to cling to their mother's fur while she flies or roosts. However many species often leave their young in a 'crèche' situation whilst she hunts. Within three weeks most bats have been weaned and their wings are developed enough to go and find their own food.

Hibernation: Many micro bats hibernate over winter, when insects are scarce. The metabolism slows dramatically during this time and they rely on their stored fat reserves. Bats are very vulnerable to any disturbance while hibernating. If they are awakened, they may use up critical energy reserves. Similarly during the day bats go into a torpor which also slows their metabolism and helps them save their energy reserves.

How to Observe Bats: The best time to see bats is at dusk. Go to a spot where insects or other food is likely to be; such as near water or a streetlight. Pick an open location where the bats will be silhouetted against a lighter sky. However remember all of Victoria's bats are fully protected species and it is illegal to collect or harm them in any way.

The 7 Bats found at Bushy Park Wetlands are -

Lesser Long-eared Bat, Nyctophilus geoffroyi.
The long-eared bats are so called because of their long, strongly ribbed ears (up to 25 mm in length) which can be folded back when at rest. These bats have light grey-brown fur on the back and paler fur below. They fly slowly close to the ground, occasionally alighting on low vegetation. They are found in urban areas. Forearm length: 35-41 mm, Body length: 40-50 mm, Weight: 6-9 gm. Echolocation Frequency 33-42 kHz.

Little Forest Bat, Vespadelus vulturnus.
This is Victoria's smallest bat. It produces a single young and roosts in tree hollows. The little forest bat has mid to dark grey fur on its back and dark grey fur with lighter tips on its belly. Forearm length: 27-30 mm, Body length: 34-48 mm, Weight: 3.5-4.5 gm. Echolocation Frequency 41-49 kHz.

Southern Forest Bat, Vespadelus regulus.
A small bat, slightly larger than the little forest bat and may be distinguished by reddish brown fur on the back and lighter brown fur on the belly. It used to be called the King River eptesicus. Forearm length: 29-33 mm, Body length: 36-46 mm, Weight: 5-5.5 gm. Echolocation Frequency 38-47 kHz.

Large Forest Bat, Vespadelus darlingtoni.
These bats are larger and have dark brown fur all over. They are found in all forest types including rainforest and catch insects from the mid canopy to the understorey. They only produce a single young at a time. Forearm length: 32-37 mm, Body length: 38-48 mm, Weight: 6-7 gm. Echolocation Frequency 37-43 kHz.

Chocolate Wattled Bat, Chalinolobus morio.
This species gets its name from its chocolate brown fur. Its lifestyle is similar to the large forest bat. The Chocolate Wattled Bat has a shorter hibernation period than other species. Forearm length: 37-41 mm, Body length: 50-60 mm, Weight: 9-10 gm. Echolocation Frequency 43-51 kHz.

Goulds Wattled Bat, Chalinolobus gouldii.
This bat has dark brown fur on the back and a black head and shoulders with lighter brown fur on the belly. Usually two young are born. They roost in colonies in hollow trees and feed on insects in the upper canopy. Forearm length: 40-45 mm, Body length: 56-75 mm, Weight: 13-16 gm. Echolocation Frequency 26-31 kHz.

White-striped Freetail Bat, Tadarida australis.
A large bat with dark brown to black fur with 2 white stripes where the wings join the belly. The ears are not joined across the top of the head and they are one of the few bats, which have an echolocation frequency low enough for us humans to hear. The lips are big and wrinkled and they have a throat pouch. They can fly fast but can't manoeuvre very well so they do most of their foraging above the tree canopy. They occupy a wide range of habitat in their search for moths and beetles. Forearm length: 59-63 mm, Body length: 85-100 mm, Weight 33-44 gm. Echolocation Frequency 10-12 kHz.

Read how the Friends erected Bat Nesting Boxes in Bushy Park Wetlands.