Rainforest Bats
Suborder Microchiroptera
-
Of the two suborders of bats,
these are the bats most people around the world are more familiar with, as they
are found practically everywhere.
-
They are a much more diverse group
than the 'Megabats'.
-
There are 17 families, 135
genera and over 759 species (Robson 2002).
-
There are microchiropterans that have evolved to feed on
insects, fish, fruit, nectar, blood and even other bats.
-
Most
live in colonies in dark places where they roost upside down.
-
They tend to be much smaller (sometimes
tiny), have tails (with the flying membrane stretching between the legs and
tail), use echolocation, are broadly insectivorous and have only one claw on the
forelimbs (Robson 2002).
-
The saying 'blind as a bat' is a reflection of the fact that many species have
small eyes and that they tend to rely on another sense to make their way around.
-
This other sense involves emitting high frequency calls from
the throat, and
projecting out the mouth or nose to detect the 'ultrasounds' as they reflect
off other objects (echolocation).
-
They use this echolocation sense both to navigate in the dark
and to locate their prey.
-
Many people around the world fear these bats for
various reasons. Many of these reasons are unfounded, but one has to admit that
when examined in the hand, they often have rather grotesque faces with various foldings in the skin. These convolutions may aid in making and collecting their
ultrasonic calls (Strahan 1998).
Suborder Megachiroptera
-
This larger family of bats has
a total of over 40 genera and over 160 species.
-
The largest, an Asian
species has a wingspan of one and a half metres (Strahan 1998).
-
Like the Microchroptera, these
animals usually roost communally, hanging upside down.
-
Unlike their smaller
relatives however, they tend not to sleep in dark places, but roost hanging off
trees.
-
And unlike the smaller bats they tend not to have tails, and have two
claws on their forelimbs (Robson 2002).
-
Also unlike their smaller relatives,
they tend to feed not so much on insects, but on fruit and/or nectar.
-
Because of
this difference in diet, much about their biology is also quite different.
-
They
generally don't have echolocation; only one African species can echolocate, but
even this is actually performed in a different way from the Microchiropteran
bats, with the clicking of the tongue, much like swiftlets (Robson 2002).
-
The lack of echolocation means
Megabats do not have the strange convoluted folds of the smaller insect bats,
and thus tend to have much simpler and more attractive fox or dog like faces.
-
Instead, they have much better developed senses of sight and smell, and these
are used in locating fragrant flowers and ripening fruit.
-
Their diet of flowers and large
fruits means they are largely restricted to the more tropical forests of the
world.
-
Of these warmer regions, they are only found in the 'Old World' of
Africa, Asia and Australasia.
-
They are notably missing from the
'new world', where some of the smaller Microchiropteran have filled in similar niches and
are even locally known as 'fruit bats' (Emmons and Feer 1990).
Evolution of the
Chiropterans
Rainforest Bats
-
The scientific name for bats (Chiroptera) originates from the Greek words of
kheir (meaning hand) and pteron (meaning wing).
-
They are
warm-blooded and have fur or hair, and feed their young with milk.
Distribution:
- Queensland is home to a recorded 52 species of bats (out of
92 species in
Australia).
- Present and past distributions of bats indicate that they originated in tropical
forests. They probably reached Australia about 26 million years ago when land connections
existed between some of the islands between New Guinea and north Queensland.
- In general, tropical non-hibernating bats are restricted to north of the Tropic
of Capricorn. Colonisation of temperate climates depends on the ability to hibernate
during seasonal food shortages such as winter.
Flight:
- They are the only mammals capable of sustained flight.
- Bats forelimbs have undergone dramatic changes during their evolution to
allow them to function as wings. They have the same basic parts as the human hand and arm,
only in very different proportions. Their upper arm is shorter, their forearm is longer,
and all the toes except the thumb are greatly elongated.
- Their wing consists of a thin membrane with a leading edge extending from the
shoulder to the base of the thumb and to the tips of the second and third toes and a
trailing edge extending from between the tips of the third, fourth and fifth toes to the
ankle. The thumb is free of the wing membrane and bears a claw for use in crawling,
support and grooming.
- Muscles that pull the forearm towards the chest mainly power flight and, to
provide a surface for attachment of these large muscles, the breastbone is keel-shaped, as
in flying birds.
Temperature Control:
- As most bats are small, they have relatively large body surface areas from which
body heat can be lost by radiation. Their extended wings can act as radiators. Warm
surroundings reduce heat loss too. Humid tropical conditions and lots of drinking water
prevent potential water loss problems.
- Bats may become torpid (dormant) in cold regions when resting by switching off
their internal thermostat and letting their body temperature drop to that of their
surroundings. This reduces the animals rate of energy consumption as its metabolism
slows and less heat is lost by radiation to the environment.
Energy and Metabolism:
- A bat must ingest larger quantities of food than a terrestrial mammal of similar
size as much more energy is spent in flying than in other modes of locomotion.
- The rate of metabolism may be as little as one percent of the rates when flying
and the heart rate may be correspondingly slower. As this state also requires some energy,
a store of fat laid down in the body of the bat in the time just prior to hibernation is
needed.
Breeding:
- Bats have two alternative reproduction cycles associated with hibernation. The
first is the storage of sperm in the female reproductive tract from autumn to spring. This
allows the female to fertilise an ovum as soon as hibernation ends. The second method is
for an ovum, usually fertilised in autumn, to develop to an early embryonic stage and then
remain at ease until spring, when development continues.
- Gestation period is between 50 and 240 days relatively long for small
mammals.
- The period of maternal dependence is also long 3 to 10 weeks.
- Usually one
young is born each breeding season.
- It is blind (except in fruit bats) and hairless.
- Females suckle their young from two nipples, one under each armpit. In some
groups there is a false (non-lactating) nipple in each groin, onto which the young may
attach itself by its teeth.
Additional Information:
- Bats have been considered as objects of mystery, superstition, fear and worship.
They are important in medical research when studying problems like hypothermia, survival
in extreme environments, and topics of comparative anatomy, embryology, histology and
cytology.
- Bats make a practical contribution to the environment in the form of tree
pollination and insect control. Flying foxes are the primary agents for pollination of
many Australian hardwood forests.
- Many bat species need protection if they are to be maintained in a sufficiently
large area, in numbers high enough for reproduction. Australia protects bats by law.
- Bats are second only in number to the rodents: about 40 percent of living mammal
species are rodents, and about 20 percent are bats.
Additional Information:
Tolga Bat Hospital
|