AnaBat system
- AnaBat system
- Overview
- Bat detection technologies
- AnaBat II Bat Detector and CF Storage ZCAIM
- AnaBat SD1
Typical monitoring approaches using Anabat
- Short-term passive monitoring
- Monitoring Stations (Long-term Passive Monitoring)
- Active monitoring
- Mobile surveys
The AnaBat bat detector system is used to identify species of bats by detecting, recording and displaying their ultrasonic echolocation calls. AnaBat detectors can be used in two principal ways - to monitor bat activity in the absence of a human operator (Passive Monitoring) or to produce realtime sonograms of calls to aid identification of bats in the field (Active Monitoring). For passive monitoring, calls can be stored to Compact Flash cards, with a single card capable of storing data for several weeks or even months. For active monitoring, the detector needs to be interfaced to a PDA (palmtop) or laptop computer by a device called a ZCAIM. [link to details]
-
AnaBat
II Bat Detector and CF Storage ZCAIM The combination of an AnaBat II Bat Detector and a CF Storage ZCAIM provides the basis for a passive monitoring station. The bat detector uses frequency division to make ultrasonic bat calls audible to humans and it also has a digital data output for call storage and display. The CF Storage ZCAIM has two roles. First, it can be used to store the data output of a bat detector onto a Compact Flash memory card, and it can simultaneously store position fixes from a suitable GPS unit. Second, it can be used, without the CF card, to interface the detector to a laptop or PDA, where the calls can be stored and displayed in real time.
More info on AnaBat II Bat Detector
More info on AnaBat CF Storage ZCAIMThe SD1 Storage Detector combines the functionality of the AnaBat II Bat Detector and the CF Storage ZCAIM into one unit. When used with a PDA, this provides realtime sonograms of bat calls from a device which can be held in one hand - an ideal tool for active monitoring. The SD1 is just as applicable to passive monitoring as the AnaBat II Bat Detector / CF Storage ZCAIM combination, and is half the size.
AnaBat
SD1 The basic role of any bat detector is to make it easier to observe wild bats through detection of their ultrasonic echolocation calls. Because bats are nocturnal and fly fast, they are often difficult to identify, even in the hand, and because they often fly tens of kilometres from their roosts to their feeding areas, they are amongst the most difficult of animals to observe and to study. Fortunately, all bats other than the megachiroptera (Flying Foxes and other closely related species) use echolocation to find their way around in the dark, to locate food and to avoid collisions with each other and with structures in their habitats. These echolocation calls reveal a bat's presence whenever it is flying or hunting, thereby providing a window into where bats are and what they are doing, in a way which doesn't interfere in any way with the bat's natural behaviour.
Echolocation calls are highly optimised for the ecological requirements of each species of bat, and therefore, different species of bats tend to produce different types of signals. This gives observers the opportunity to identify which species of bats are being detected without having to capture them. In practice, this is much harder than it might seem, because bat calls vary greatly depending on where the bat is flying in relation to structures, and also according to what the bat is trying to achieve. This variation far exceeds the differences between species, so in order to identify bats acoustically, it is necessary to have an adequate understanding of each species' echolocation behaviour under a wide range of conditions. In practice, species which are very different often have surprisingly similar calls, while closely related species, which might be difficult to distinguish even in the hand, are sometimes quite easily identified by call. Therefore, a combination of visual and acoustic observations is usually the best way to identify species.
Bat detectors can be used in two fundamentally different ways. Firstly, they can be used to watch bats in the field in much the same way bird-watchers watch birds. In this case, called Active Monitoring, a bat detector, and often a spotlight, are used instead of binoculars. Visual observations give the observer information about the bat's behaviour, where it is flying, its flight style and wing shape, and other morphological features, such as ear length, tail length and fur colour. Acoustic observations give the observer information about the types of calls produced by a bat, with the most basic parameters being the frequency of the call (its pitch), the shape of the call (how the frequency changes in time) and the rate at which calls are produced. The combination of visual and acoustic observations also enhance the identification process by providing a context in which to interpret the calls. For example, when the observer knows where the bat is flying, it becomes easier to understand how loud the call is, and how that call fits into the species' repertoire. Active monitoring is the best way to identify free-flying bats, but to be effective, it requires a great deal of skill on the part of the observer.
The other major way in which bat detectors are used is called Passive Monitoring. In this approach, there is no observer present, and bats which pass near enough to the monitoring unit are recorded and their calls stored for later analysis. The bat detector effectively becomes a bat activity data logger. It is much more difficult to identify many bats through passive monitoring, because of the lack of visual and contextual observations. However, Passive Monitoring has many advantages which result from the far greater sampling effort it enables for a given resource commitment.
A Passive Monitoring station can operate all night, every night for weeks or months or years with very little human interaction, so it is extremely well suited to determining temporal patterns of activity, which in turn can provide basic information about what a place means to bats. Other benefits accrue from the sampling effort achievable. For example, rare bats are much more likely to be detected than by other methods, because exposure to the possibility of detection is so much greater.
Passive Monitoring opens up whole new frontiers of bat research, by enabling long term observations on how bats use their environment without interfering with the bats. Data collected by Passive Monitoring stations can be manually scanned by people with the expertise to identify the bats recorded, but there is also great potential for the use of software designed to automate the identification process. This approach has its limitations, because of the lack of contextual information and the inherent problems in bat acoustic identification, but it is already a useful tool which can, for many purposes, be used to deal with the large amount of data which can be collected. Such automated identification provides other benefits, by freeing the identification process from the biases of human subjectivity, and by allowing bats to be usefully surveyed by interested parties without the expertise to make the identifications themselves. Automated identification techniques are still in the early stages of development, and it is to be expected that this approach will become even more useful in the future.
The AnaBat SD1 Compact Flash Bat Detector is designed to provide the functionality necessary for operation in both Active and Passive Monitoring modes. It has many features which have been specifically designed with both these roles in mind and which have been found to be important after many years of experience using earlier models for these purposes.
Most bat echolocation calls are ultrasonic, which means they cannot be heard by unaided human hearing, and this is why a bat detector must be used before humans can make use of these signals. In general, bat detectors have two roles. The first is to make a signal audible to humans, thus revealing the presence of the bat and allowing the operator to get some information about the nature of its calls from their sound. Because humans are relatively poor at characterising brief, simple sounds like bat calls, it is usually important to take a second step, which is to make the signal visible through some kind of sound analysis, so that its important characteristics can be seen in more detail. Traditionally, two methods have been used to enhance human perceptions of bat sounds.
Heterodyne bat detectors can be tuned so the call frequency can be determined from the frequency to which the detector is set. This is the most sensitive approach to bat detection, and more detail can be elicited by very skilled users by re-tuning the detector so some idea can be gained of how the signal varies across a range of frequencies. However, this process is slow, and requires repeated encounters with the same bat. Heterodyne techniques also have the disadvantage that a bat cannot be detected unless the tuning is roughly correct, which means the detector must be continually scanned across a range of frequencies in order to detect different species of bats, further reducing responsiveness of the system.
Another disadvantage is that heterodyne output signals are of no use for further analysis using more sophisticated sound analysis techniques.
The other commonly used technique is time-expansion, which has the same effect as recording the sound on a high speed recorder then playing it back at a much reduced speed. This reduces frequencies to make them audible and also slows down the sound so it is more easily perceived by humans. The trouble with time-expansion is that it takes much longer to listen to the calls than it does to record them, so it is not a realtime process. There is also no immediate feedback of the frequency of the call, which must be judged by human hearing or analysed in more detail later on by analysis of the recordings.
For field use, both heterodyne and time-expansion techniques rely heavily on human hearing as the main way to interpret call details. AnaBat has taken a completely different direction, instead relying on techniques called frequency division, to make calls audible, and Zero-Crossings Analysis (ZCA) to make them visible. These techniques make it possible to see sonograms of bat calls in real time, so for field use, the emphasis is taken off human hearing as the primary agent of analysis, and instead is placed on the visual sense, which is far more effective for assimilating the fine detail required. Sonograms are graphs of call frequency against time, which show the frequencies and shapes of calls in ways which are immediately meaningful to human users. They provide access to details of bat calls at a much finer level than is possible by hearing alone, and they provide this access to users without any requirements for exceptional hearing abilities. There is no tuning requirement, no lag between recording and display, and no need for repeated encounters with the same bat.
Frequency division has often been criticised for its incomplete representation of bat calls and its relatively lower sensitivity. In reality, any bat detector technology ends up being a tradeoff between many competing desirable traits and technological limitations. Lower sensitivity, for example, needs to be seen in the context of what the technology can achieve in relation to other technologies which provide inherently higher sensitivity. Even at the simplest level, lower sensitivity can't be equated to the detection of fewer bat calls, because other factors also affect how many calls can be detected and how those calls can be used.
In practical terms, the frequency division technique used by AnaBat detectors has been found to be highly effective for almost all purposes for which bat detectors are used, and it has led the way in making it feasible to deploy long-term Passive Monitoring stations and in providing realtime sonograms of bat calls in the field. The AnaBat SD1 Compact Flash Bat Detector has pushed the limit further by making it possible to display realtime sonograms on a unit which can be held in one hand. This is only possible because this bat detector uses frequency division technology, which is exceptionally well suited to the task in its speed of operation, low power consumption and highly efficient storage capabilities, making it possible to build into the detector all the functionality required to interface directly to a PDA.
Typical monitoring approaches using Anabat
In many situations, it is productive to implement short-term passive monitoring to run alongside other bat sampling techniques. In this scenario, a passive monitoring station can be used as one of several tools employed to survey bats at a site of interest. Because of the short-term nature of this application, power supply requirements are much less complex, and in many cases, it may not even be necessary to implement weather protection (link to Weather Protection).
Short-term passive monitoring is often used alongside mistnets or harp traps to provide an acoustic component to a capture-based survey. The power of this approach comes from the fact that often, perhaps usually, there is some proportion of the local bat fauna which is easier to detect and identify acoustically than to capture. Even if the species cannot be identified, the acoustic record can often show the presence of additional species which have eluded capture.
Passive monitoring is useful even as a compliment to active monitoring. Although active monitoring will produce better recordings and visual information which can help identify bats, passive monitoring provides a different picture of bat activity. Passive monitoring avoids any observer biases and because it can run all night without getting tired, it gives an unbiased view of how activity varies throughout the night. Furthermore, passive monitoring avoids any interaction with the bats being observed, while active monitoring is potentially subject to effects of the monitoring on bat behavior. The combination of active and passive monitoring is often more productive than either alone.
For short-term passive monitoring, it is possible to use either the combination of Anabat II detector with the Storage ZCAIM, or the SD1, which combines the functions of these two units. The SD1 is more compact, and can run for a whole night on a single set of four AA batteries, while the combination requires an additional 9V battery for the detector.
Monitoring Stations (Long-term Passive Monitoring)
Monitoring stations for long-term passive monitoring are essentially data loggers designed to be left in the field for extended periods, where they record bat calls without human intervention. Typically, they will be left in a single location for weeks, months or years, so they must be set up in ways which protect them from the weather and human interference and where they can be supplied with a reliable power source (e.g. Solar power). Weather Protection
Monitoring stations are the natural choice for any situation where it is desirable to gain insights into the temporal aspects of bat occurrence.
However, they can also provide a unique picture of bat usage of a study site, because the huge sampling effort they accomplish can vastly increase the probability of detection of rare and difficult-to-identify species, compared to other methods.
Monitoring stations have the potential to reveal patterns of dispersal and migration in bats, but they could also be used in the very long term to assess population trends.
For long-term passive monitoring, it is possible to use either the combination of Anabat II detector with the Storage ZCAIM, or the SD1, which combines the functions of these two units. The SD1 is more expensive, but better able to deal with fluctuating power supply voltage, such as could occur with a battery which is charged by a solar panel.
In active monitoring, an observer watches bats much as a bird observer would watch birds. The observer actively searches for bats, and then uses a combination of acoustic and visual cues to help make identifications. In active monitoring, the observer can often track a detected bat by keeping the detector pointing towards the bat, producing longer sequences of better quality calls and aiding species identification. The combination of acoustic and visual cues greatly improves the chances of identifying bats compared to using either alone, because some bats are easier to identify visually, while others are easier acoustically.
Active monitoring is perfect for surveys based on walking transects. To assist this sort of activity, the use of a GPS is tightly integrated into the Anabat system, allowing a complete record to be kept of where the observer was at any time, how long was spent in any area and where each bat was recorded. If a PDA is used, a map of GPS fixes is provided by the AnaPocket application, allowing the observer to check their position at any time against the path already taken.
Using Anabat, it is possible to combine visual observations of the bats with realtime sonograms of the calls displayed on either a PDA or a laptop. If a PDA is used with an SD1, this gives the observer unprecedented mobility, because a single, hand-held unit can produce realtime sonograms while also taking care of storing recorded calls and keeping track of position fixes from a GPS. Another advantage of the SD1 is that it is possible to set the division ratio independently for the audio output and the data stream, allowing higher resolution recordings without compromising the audibility of the speaker output.
In mobile surveys, bat detection is carried out from a vehicle moving along a transect at a speed which effectively precludes detection of the same bat more than once. Mobile surveys sacrifice temporal detail at a single site for coverage on a much broader spatial scale. However, they can provide extra insight, because the low probability of detecting the same bat more than once means the resulting activity levels can be meaningfully related to actual population densities.
Mobile surveys can be carried out either passively or actively, or they can bridge the gap between the two. In active mobile surveys, an observer takes an active role in searching for, and identifying bats. An example would be an observer watching bats from the open back of a pickup truck. This approach gives the observer the chance to improve acoustic detection by keeping the detector pointing towards a bat, and to use visual and behavioral cues to assist in identification.
In passive mobile surveys, human intervention is limited to providing the transport. An example would be a passive detector mounted on a car (or train or ferry) which transports the detector along a transect. The driver need not be aware of when bats are detected, or even that the detector is present.
For either passive or active mobile surveys, the tight integration of GPS compatibility into the Anabat system is a vital component, since in driving surveys, knowledge of the vehicle's position at any time during the survey is essential, as is the location of any bat recorded. A GPS system can be hooked up directly to the Storage ZCAIM or SD1 if data is being stored on a CF card, or a Bluetooth GPS can be used with a PDA if calls are being monitored and recorded using AnaPocket.
For driving surveys, it is possible to use either the Anabat II/Storage ZCAIM combination or the SD1. Recorded calls can be stored either to CF card or directly into a PDA or laptop. If the driving survey is being conducted with active monitoring, the SD1 would be the better choice, because it provides separate audio and data division ratios, allowing higher resolution recordings without compromising the audibility of the speaker output.
Anabat is a complex system with many features built in to aid data management and analysis. In addition, some of the skills needed to most effectively use the system are more easily taught through hands on experience.
Training courses and consultation are available either on a request basis or as part of courses offered in various locations around the world. Please check here for upcoming courses with open enrolment. For groups needing training or individuals needing specialized skills, please contact us for information about the availability and cost of special trainings or consultation.
|
Industries serviced Bat researchers |
Related links |
© Copyright 2006 Titley Electronics. All rights reserved. Design by PROdesign.