bat detectors

Bat Detectors

Luckily technology can help us to 'spot' bats and to learn more about their lives. Bat detectors are small electronic devices, which allow us to listen to bat calls. They pick up the inaudible ultrasonic echolocation calls the bats emit and make them audible to humans. This allows us to easily detect the presence of bats in an area. Much can be learnt from listening and studying these echolocation calls, for example separate species can sometimes be recognised. Being relatively simple to use, even amateurs or beginner's can use bat detectors without the need for training, there is also no danger of affecting the bats, as bat detectors do not interfere with the bats in any way. There are a number of different types of bat detector available. The cost of the detector depends on the method it uses to collect and analyse the sound. As with most electrical appliances, the most complex and advanced versions cost the most money. Relatively simple bat detectors, suitable for amateurs cost between £40 and £250. More sophisticated detectors with specialised recording and analysis facilities can cost many thousands of pounds. Basically there are three different types of bat detector, which work on three different principles. These are heterodyne detectors, Frequency division detectors and time expansion detectors.

Heterodyne Detectors

This is the simplest kind of detector and they are the most common type of detector seen because they are the cheapest to buy. They have a tuning control knob somewhat like those seen on old-fashioned radios where you had to tune into the frequency you wanted to listen to. These detectors must likewise be tuned to the correct frequency for the species of bat, which you want to listen to. The radio receiver has only a very narrow bandwidth, which means only a very narrow range of frequencies, can be listened to at once. Much as in the same way that by tuning a radio you can only listen to one station at once, with this type of detector only one species of bat can be listened to at one time. Heterodyne receivers have an ultrasonic microphone, which picks up the echolocation calls of the bats. These calls are mixed in an oscillator. This is something which brings the frequency of the bat call down to a level at which we can hear it. A more advanced type has two oscillators and is known as a super heterodyne. The advantages of heterodyne detectors is that they are cheap and effective. They are easy to use. Using this type of detector allows you to determine to a certain extent what type of bat you have detected. For example, Noctules use low frequencies of around 20 kHz, by listening to this frequency you should be able to hear this type of bat, however some other species such as the Leisler's and Serotine also use similar frequencies, so determining exactly which species you have is difficult. The problem is worse for the Myotis species, as most have calls in the range of 40-60 kHz, and trying to tell exactly which species you have is pretty much impossible. Some people claim that they can identify separate species by learning the special characteristics of each species call, for example the speed at which it is emitted, its strength etc. However in practise, and especially for beginners' this is pretty much impossible and even professionals cannot be sure exactly and can only hazard a guess. Another problem with this type of detector is that it can be difficult to tune into the correct frequency when a bat is flying quickly overhead.

Frequency Division Detectors

These type of detectors work by dividing the ultrasonic call it receives down in frequency to cover the human range of hearing. This is done by using a zero crossing detector. This type of detectors is useful because it detects the calls along the whole ultrasonic frequency range at the same time. This means they do not need tuning. This makes life a lot easier for the operator. Spectrograms can also be produced by using this type of detector, which allows calls to be studied in more detail and allows species to be correctly identified. The main disadvantage of this type of detector is that they tend to pick up a lot of background noise.

Time Expansion Detectors

These are the most recent and the most expensive type of bat detector available. They are typically only used by bat specialists and researchers. They use digital technology, and work by collecting bat calls and then playing them back at a slower rate, and therefore at a lower frequency, which is audible to humans. As they collect signals from the whole ultrasonic spectrum no tuning is necessary. The slowed down signals can be saved and then recorded onto tape and then downloaded onto a PC for analysis. This type of detector keeps all the subtle properties of the bat call, unlike other types of bat detector, so is ideal for detailed study of bats. This type of detector is the one most favoured by professionals and bat researchers, but is quite expensive.

Species Identification with a Heterodyne Detector

Is it possible to distinguish between different bat species when using this type of bat detector? Some people using heterodyne detectors claim to be able to use the varying sounds produced by bats to be able to recognise the different species. Such claims should be treated with caution. The sounds produced by a heterodyne detector are so variable; it is almost impossible to be precise when deciding which species is which. However it is possible to determine bats from certain groups are present, as mentioned above.

However the differences which people have noticed will be mentioned to help you should you decide to try to hazard a guess. Pipistrelles use frequencies of about 45-55khz and there calls tend to sound like 'smacks', these are often irregular and can vary in pitch. Daubenton's, Whiskered and Brandt's Bats all have calls with fast repetition rates. The call of the Natterer's Bat though is faster, but more quiet and irregular than these other Myotis species. The Long eared bats also have faster repetition rates than other Myotis species, but the calls are much quieter, often not being picked up more than a few metres away from the detector. However, these differences should not be relied upon, as they are not always present or noticeable. The Horseshoe Bats have echolocation calls with much higher frequencies than the other species. The Greater Horseshoe bat being about 80 kHz, while the Lesser Horseshoe Bat uses frequencies even higher at roughly 110-120 kHz.

Spectrographic Analysis

The calls saved on time expansion detectors can be analysed on a PC using special sound analysis packages. Sonograms, which are a visual representation of sound, can be produced. These enable sounds to be compared and analysed. From a sonogram many things can be seen, such as the beginning and end frequency of the bat call, how long the calls last, and the exact length of time between calls. Sonograms are mainly used by scientific researchers studying the properties of bat ultrasonic calls.

British Bats

Home		Bat Detectors Luckily technology can help us to 'spot' bats and to learn more about their lives. Bat detectors are small electronic devices, which allow us to listen to bat calls. They pick up the inaudible ultrasonic echolocation calls the bats emit and make them audible to humans. This allows us to easily detect the presence of bats in an area. Much can be learnt from listening and studying these echolocation calls, for example separate species can sometimes be recognised. Being relatively simple to use, even amateurs or beginner's can use bat detectors without the need for training, there is also no danger of affecting the bats, as bat detectors do not interfere with the bats in any way. There are a number of different types of bat detector available. The cost of the detector depends on the method it uses to collect and analyse the sound. As with most electrical appliances, the most complex and advanced versions cost the most money. Relatively simple bat detectors, suitable for amateurs cost between £40 and £250. More sophisticated detectors with specialised recording and analysis facilities can cost many thousands of pounds. Basically there are three different types of bat detector, which work on three different principles. These are heterodyne detectors, Frequency division detectors and time expansion detectors. Heterodyne Detectors This is the simplest kind of detector and they are the most common type of detector seen because they are the cheapest to buy. They have a tuning control knob somewhat like those seen on old-fashioned radios where you had to tune into the frequency you wanted to listen to. These detectors must likewise be tuned to the correct frequency for the species of bat, which you want to listen to. The radio receiver has only a very narrow bandwidth, which means only a very narrow range of frequencies, can be listened to at once. Much as in the same way that by tuning a radio you can only listen to one station at once, with this type of detector only one species of bat can be listened to at one time. Heterodyne receivers have an ultrasonic microphone, which picks up the echolocation calls of the bats. These calls are mixed in an oscillator. This is something which brings the frequency of the bat call down to a level at which we can hear it. A more advanced type has two oscillators and is known as a super heterodyne. The advantages of heterodyne detectors is that they are cheap and effective. They are easy to use. Using this type of detector allows you to determine to a certain extent what type of bat you have detected. For example, Noctules use low frequencies of around 20 kHz, by listening to this frequency you should be able to hear this type of bat, however some other species such as the Leisler's and Serotine also use similar frequencies, so determining exactly which species you have is difficult. The problem is worse for the Myotis species, as most have calls in the range of 40-60 kHz, and trying to tell exactly which species you have is pretty much impossible. Some people claim that they can identify separate species by learning the special characteristics of each species call, for example the speed at which it is emitted, its strength etc. However in practise, and especially for beginners' this is pretty much impossible and even professionals cannot be sure exactly and can only hazard a guess. Another problem with this type of detector is that it can be difficult to tune into the correct frequency when a bat is flying quickly overhead. Frequency Division Detectors These type of detectors work by dividing the ultrasonic call it receives down in frequency to cover the human range of hearing. This is done by using a zero crossing detector. This type of detectors is useful because it detects the calls along the whole ultrasonic frequency range at the same time. This means they do not need tuning. This makes life a lot easier for the operator. Spectrograms can also be produced by using this type of detector, which allows calls to be studied in more detail and allows species to be correctly identified. The main disadvantage of this type of detector is that they tend to pick up a lot of background noise. Time Expansion Detectors These are the most recent and the most expensive type of bat detector available. They are typically only used by bat specialists and researchers. They use digital technology, and work by collecting bat calls and then playing them back at a slower rate, and therefore at a lower frequency, which is audible to humans. As they collect signals from the whole ultrasonic spectrum no tuning is necessary. The slowed down signals can be saved and then recorded onto tape and then downloaded onto a PC for analysis. This type of detector keeps all the subtle properties of the bat call, unlike other types of bat detector, so is ideal for detailed study of bats. This type of detector is the one most favoured by professionals and bat researchers, but is quite expensive. Species Identification with a Heterodyne Detector Is it possible to distinguish between different bat species when using this type of bat detector? Some people using heterodyne detectors claim to be able to use the varying sounds produced by bats to be able to recognise the different species. Such claims should be treated with caution. The sounds produced by a heterodyne detector are so variable; it is almost impossible to be precise when deciding which species is which. However it is possible to determine bats from certain groups are present, as mentioned above. However the differences which people have noticed will be mentioned to help you should you decide to try to hazard a guess. Pipistrelles use frequencies of about 45-55khz and there calls tend to sound like 'smacks', these are often irregular and can vary in pitch. Daubenton's, Whiskered and Brandt's Bats all have calls with fast repetition rates. The call of the Natterer's Bat though is faster, but more quiet and irregular than these other Myotis species. The Long eared bats also have faster repetition rates than other Myotis species, but the calls are much quieter, often not being picked up more than a few metres away from the detector. However, these differences should not be relied upon, as they are not always present or noticeable. The Horseshoe Bats have echolocation calls with much higher frequencies than the other species. The Greater Horseshoe bat being about 80 kHz, while the Lesser Horseshoe Bat uses frequencies even higher at roughly 110-120 kHz. Spectrographic Analysis The calls saved on time expansion detectors can be analysed on a PC using special sound analysis packages. Sonograms, which are a visual representation of sound, can be produced. These enable sounds to be compared and analysed. From a sonogram many things can be seen, such as the beginning and end frequency of the bat call, how long the calls last, and the exact length of time between calls. Sonograms are mainly used by scientific researchers studying the properties of bat ultrasonic calls.
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