Why Bat Detectors?
The
frequency of the echolocation sounds that bats produce, is out of the
range of human hearing. In order for humans to hear the calls of
bats, bat detectors have been developed.
While human hearing can only detect sounds within the 0
to 16kHz range, the call frequency of bats ranges from 20 to 210kHz with
each bat species having a unique call. Bat
detectors convert the ultrasonic calls into audio which we can hear, enabling us to identify
different species and to note various behavioural patterns. Much of this
can be done without ever seeing the bats.
Bat detectors range from simple devices which merely
allow one to ‘hear’ the bat to highly sophisticated detectors which
can, once coupled to a computer, allow one to ‘hear’ and ‘see’
the call through sonographs.
Is a Bat detector only for
Scientists?
NO!! Anyone
fascinated by bats will be richly rewarded by discovering more secrets
of bats, their hiding places and their identity with the aid of a bat
detector.
A bat detector is as useful
to the bat enthusiast as binoculars for the bird watcher!
There are various types of
detectors available on the market and may be purchased for as little as
R1000!
Types of Bat Detectors
Bat detectors can be divided up into three basic types
although some can combine the Heterodyne and time expansion modes.
A. Heterodyne
bat detectors
The receiver converts the noise made by bats into
sound that we can hear. They can be tuned into a number of
different frequencies which allow one to listed to a wide range of
species. Depending on the species of bat being listened to, the
calls sound like a series of clicks which are either dry and crackly
or wet and gurgly. Until a bat locks onto an item of food, it
emits calls at fairly regular intervals. Once it finds a
suitable insect, the rate of the calls emitted speeds up and this
sounds like a buzz on the bat detector. This is known as a ‘feeding-buzz’.
One can thus not only identify the species but also determine whether
or not the bat is feeding. This type of detector is fairly
inexpensive.
B.
Frequency division bat detectors
These record one pulse out of every 8 to 10 incoming
pulses thus reducing a 56kHz call to a 7 or 5.6kHz call which is
audible to humans. Without computer software, these detectors
merely tell you that a bat is present. However, once the sound
is analysed on computer, the species can be identified. These
detectors are more suited to researchers than the bat enthusiast.
C.
Time expansion bat detectors
These are very expensive detectors and work in much
the same way a high-speed tape-recorder does. They record the
sound and then play it back at 10, 32 or 64 times slower to make the
sound audible to humans. These systems not only enable one to
identify the species but also the amplitude, frequency and harmonic
detail of the call.
