Following the acquisition of EFE & GB Nets earlier this year, NHBS now manufactures a wide range of plankton nets at our workshop in Devon. Nets are available with an opening diameter of 250mm, 300mm or 500mm and with mesh sizes ranging from 10µm to 500µm.
250mm and 300mm diameter nets
250mm diameter plankton nets are available with 10µm to 250µm mesh
250mm and 300mm diameter nets have a stainless steel frame to which a 500mm long bag is attached. They are supplied with a harness and seven metre long towing line which can be used to tow the net behind a boat or from a suitable bank or jetty.
The standard cod end is fitted with a filter in the same mesh size as the main part of the bag. However, various alternatives can be selected at the time of ordering. Options include a clear extension tube, collecting bottle, tap valve or large filter fitted in place of the standard filter. It is also possible to have weight loops added to the end of the net (weights not included) or a stainless steel swivel to be used on the harness in place of the standard nylon ring.
The heavy duty upgrade uses heavy duty nylon for the net collar and cod end collar and also includes fully taped seams.
500mm diameter nets
500mm diameter bags have industrial nylon collars and reinforced seams
500mm diameter nets have a stainless steel frame and 1900mm long bag and a three point harness with swivel connector. All seams are reinforced and the collar is made from industrial nylon for added strength and durability. The cod end of the bag is fitted with a heavy duty screw-on filter in the same mesh size as the bag. This net is not supplied with a towing rope and so users will need to supply their own rope or chain which can be fitted to the harness.
As with the smaller plankton nets, various adaptations are available in order to create a net which is suited to your sampling needs. A flexible cod end extension allows a greater sample volume to be collected and also lets you connect a different filter type. A replacement cod end cap provides a closed ended option and results in a sample size of 700ml and a quick release bag is ideal for collecting fry or elver or for when a rapid changeover of bags is required.
Net bags and the educational plankton net
Educational plankton net
As well as standard plankton nets, we also stock a range of plankton net bags designed to fit onto the professional hand net frame. These fit onto the frame in the same way as the standard hand net bags, and have a detachable screw-on filter in the centre. An educational plankton net with 150µm mesh is also available for school use or for those who require an economical net for trial sampling.
Susan Young – Author of CCTV for Wildlife Monitoring
Susan Young is a writer and photographer with a background in physics and engineering. She is the author of the fantastic CCTV for Wildlife Monitoring published earlier this year. This great handbook provides lots of practical information on the use of CCTV for survey and research.
Your book on CCTV for Wildlife Monitoring, published earlier this year, is packed full of practical information for the researcher or amateur naturalist interested in using CCTV to monitor wildlife. Could you explain a little bit about your professional background and how you came to write this book?
I have had a very varied career and have always tended to look for new ways to do things. After graduating, I worked using applied physics in the manufacture of aero engines, and later, after a Masters in Engineering Management, worked in a large electronics company. For the last 15 years I have been a writer and (mainly) wildlife photographer, and found my experience of great value with the more technical aspects of photography.
After using various photographic systems for recording wildlife, I came to believe that CCTV had many applications for both the amateur and professional naturalist. As I have always enjoyed doing something different, I spent the last few years researching CCTV systems for use with wildlife.
I wanted to test CCTV in more formal environments and thus I volunteered for Natural England and the Wildlife Trust. With Natural England I have been researching the use of an underwater system for studying fish in rural rivers, and have also developed a system for monitoring rock pool life. With the Woodland Trust I have developed a portable CCTV system for bat monitoring, which is being used for a research project at the moment, and which can greatly reduce the need for night emergence surveys.
With this research I became convinced that there were many applications where CCTV could be of great benefit, but that the lack of clear, relevant technical information was a barrier to wider use. The more I discovered about CCTV, the greater my enthusiasm for the subject, and the greater the number of applications that became apparent. For this reason I decided to write CCTV for Wildlife Monitoring with the aim of encouraging wider use of what I believe is a valuable tool.
Do you feel that there is a need to bridge the knowledge gap between manufacturers/engineers and the individuals using field equipment? As an extension of this, do you feel that it would improve the quality of research or survey data if people had a better understanding of the functions and limitations of their kit?
In meeting both professional and amateur naturalists, I have often heard it said that manufacturers/engineers do not understand their problems. Without that understanding, they are unable to advise on the areas of use. In addition, the biological sciences are not generally taught with an emphasis on technology, which can leave graduates unfamiliar with technical language. Companies such as NHBS and, hopefully, books like mine, can help to bridge what is a very large gap in communication.
I feel very strongly that there could be great steps forward in research and survey methods if people were more aware of the possibilities of their equipment, together with an understanding of the limitations. For the keen naturalist, there is also a great number of applications for filming for pleasure.
We have found trail cameras to be extremely popular both with amateur naturalists and researchers. How do you feel these compare with CCTV systems and in what types of situations would you recommend each of them?
This is a difficult question to answer briefly!
I have used trail cameras for many years and without doubt they are of great value for indicating the presence of wildlife, especially in remote areas, but their short filming time makes them less practical for monitoring. CCTV is much more flexible and responsive, and has the capability of giving higher quality images, especially at night. CCTV can be used with underwater cameras, and with cameras that fit into small spaces such as bird or mammal boxes.
One of the main advantages of a CCTV system is that it can be set up to record at certain times as well as being triggered by motion or event. The wide range of CCTV cameras means that variable focus lenses can be used, allowing one to zoom in to the subject, noise reduction can produce clean images and features such as ‘smart IR’ prevent over exposure of nearby objects, a problem with night images with trail cameras.
If mains power is available, the advantages of CCTV become more apparent. Recent technology means that HD cameras can be used, giving high quality HD videos, and images can be viewed live on a monitor. If the internet is also available, images can be viewed remotely by smartphone, tablet or PC.
HD analogue video (AHD or, more recently, HD-TVI) is an amazing step forward in CCTV, giving videos of great quality at a reasonable cost and without the complexity of more traditional HD methods which require some knowledge of computer networks.
You have a vast amount of experience in the field using CCTV and must have collected huge amounts of footage from this. How does it make you feel when you are reviewing your videos and come across something amazing? Do you have a single favourite video or image?
There is nothing to beat the excitement of coming across a video of something unexpected. The otter swimming underwater was caught by accident while filming fish and is very short, but still very exciting, and something I never really expected to get, although I was always hoping. I try to plan a CCTV session to reduce the number of ‘empty’ videos and to make sure that I review small numbers without letting them build up over days. That way, the excitement is always there.
Finally – if you could set up a CCTV system anywhere in the world, where would you choose?
I would choose the UK. UK wildlife is very elusive and offers a great challenge. I am an ‘otterholic’ and would love to set up cameras on the Shetland islands. I have photographed otters with a DSLR, but there is nothing to beat the excitement of filming otters in action.
As part of their Heritage Ability project, Living Options Devon recently hosted the UK’s first ever Deaf-led bat walk at the Love Parks event, in Cockington Park, Devon.
NHBS are delighted to have been able to loan them an Echo Meter Touch bat detector from Wildlife Acoustics, which allowed the attendants to view live sonograms on an iPad – whilst receiving further information in British Sign Language from the guide, Alasdair Grant.
This fantastic event was part of a whole day of activities helping to make heritage sites more accessible for disabled and Deaf people.
Alasdair, Deaf Alumni Programme Manager for Deaf Unity, who is working towards his bat license, led an inspiring bat walk which one participant said was “a memorable and unique experience”. The walk included watching soprano pipistrelles and lesser horseshoe bats exiting their roosts in outbuildings in Cockington Court, and common pipstrelles, serotine and noctule bats feeding in the park and lakes area.
The walk provided a unique opportunity for Deaf people to see and learn more about the lifestyle of our British bats and how to identify different species using bat detectors with visual sonograms rather than by sound. The Echo Meter Touch connects to an iPad to provide an excellent and very accessible visual display of bat calls in real time.
Living Options and Deaf Unity very much hope to run further bat walks in the future and would be delighted to advise other organisations and bat groups on how to lead bat walks for Deaf people.
The Heritage Ability Project supports heritage sites in South West England to improve accessibility for disabled people. Funded by the Heritage Lottery Fund, the project is currently piloting different approaches with partner sites including museums, country parks, nature reserves and historic houses.
Best bat detectors for bat walks
Echo Meter Touch
This tiny ultrasound module connects directly to your Apple device and lets you listen to bat calls in real time as well as viewing a live sonogram on your screen. Ideal for bat walk leaders, the Echo Meter Touch provides you with plenty of real time information to share with your group, as well as letting you record and classify calls so you can provide a later update of all species heard during the walk.
Elekon Batscanner
The Batscanner is one of the simplest bat detectors on the market – simply turn it on and listen. The device will automatically tune to the frequency of the bat call nearby and will display this frequency on the LCD screen whilst playing the sound back at an audible level.
SSF Bat2
The SSF Bat2 cleverly scans all frequencies simultaneously and will jump to the peak (loudest) frequency at the touch of a button. Pre-programme up to four fixed frequencies and view a small spectrogram of the received call. Ideal for beginner or seasoned bat walkers.
Magenta Bat 4 and 5
The Magenta Bat 4 and Magenta Bat 5 are our most popular detectors for beginners. Affordable to buy and simple to use, they convert the call produced by the bat into a sound which is easily heard through the speaker. Simply tune to the required frequency using the large dial on the front of the unit. The Bat 5 also has a digital display which makes tuning the detector even easier.
The bat survey season is just beginning and since our last update in November 2015 many of the new bat detectors have arrived in stock and we have received some customer feedback and updates on specifications from manufacturers. The total count of new bat detectors now stands at six – three passive full spectrum recorders from Elekon, two passive recorders in the Song Meter family from Wildlife Acoustics, and the handheld Anabat Walkabout from Titley Scientific.
Song Meter SM4BAT
We have had the Wildlife Acoustics SM4BAT FS in stock on and off now for the last few weeks (supplies have been limited) but we now have plenty on the shelves. We are really impressed with these units – they are smaller, lighter and easier to programme than the old Song Meters and have massively improved battery life (up to 45 nights for the FS and 70 nights for the ZC). They come in a strong lockable enclosure that can easily be chained to a tree and include a 3m microphone cable when purchased with the SMM-U1 microphone. The ZC units have not arrived yet but are expected in early April. The SM4BAT detectors also include an incredible three year warranty (excluding the microphones).
Wildlife Acoustics have also announced that they are phasing out the EM3+, the SMZC and the SM2BAT+, which are being replaced by the Echo Meter Touch, SM4BAT ZC and SM3BAT / SM4BAT respectively.
Elekon Batlogger C
Elekon have now released three new passive bat detectors within the last few months which are based around the very highly regarded Batlogger M handheld bat detector. The Batlogger C is probably the highest specification bat detector on the market today – it has everything you would expect from a high end passive detector including programmable recording schedules, fully weatherproof enclosure, and high quality full spectrum recordings as well as many extras. These include optional sms and/or email messages reporting the status of the unit and the number of recordings made as well as the amount of power remaining. Furthermore, because the Batlogger C also has in-built GPS it can send you an alert if the unit is moved. A wide range of power options are available: a 50 hour rechargeable battery is included and there is space for a second. Mains power is also an option as is solar power which requires the addition of the Batlogger C solar panel. When used with two 50 hour batteries, just half a day of sun in every 10 days should be enough to keep the Batlogger C powered indefinitely.
Elekon Batlogger A+
Also from Elekon, the Batlogger A family – the A and the A+ are new miniaturised passive bat detectors. Both are programmable, are housed within a small weatherproof enclosure and include a Knowles FG microphone on a 2m extension cable. The Batlogger A will record for up to 30 hours on eight AA batteries (e.g. three 10 hour nights). The Batlogger A+ was created after a customer contacted Elekon to say that the Batlogger A looked perfect for installing up trees and in other inaccessible location but that ideally, the battery life should be longer. In response the team at Elekon quickly created the new Batlogger A+ which is slightly larger than the Batlogger A but includes the same rechargeable lithium ion battery used in the Batlogger C. This will power the A+ for up to 70 hours. Stock of both models are fairly limited so please contact us soon if you would like to place an order.
Anabat Walkabout
A few software glitches delayed the release of the Anabat Walkabout in 2015 but this incredible new bat detector has now been in stock for several months. The touch screen Android tablet based bat detector not only records any passing bats but also lets you view the sonogram in real time in both full spectrum and zero crossing formats. A GPS, lux-meter, thermometer and humidity sensor are all in-built so not only will each call be geo-tagged but you will also be able to collect the full range of environmental data for each transect without needing any additional tools. A fully charged unit will last for around eight hours. The Walkabout bundle will soon also include a copy of Analook Insight analysis software to allow you to view and analyse full spectrum and zero crossing recordings.
If you would like any help, advice, or a short loan of one of our demo bat detectors please get in touch with our Wildlife Equipment Specialists on 01803 865913 or customer.services@nhbs.com.
The LED Lenser P17.2 and H7.2 are just two additions to our lighting range.
Ecologists use torches for a wide range of applications including newt surveys, for note taking and safety during nocturnal surveys and to look for roosting bats and other creatures within lofts and other confined spaces. Each application requires different things from the torch – high power for newt surveys, a red filter to preserve night vision, light weight and / or hands free operation to reduce fatigue, a long operating time, lower power settings to reduce disturbance and an LED bulb to reduce heat output. So far, we know of no single torch that combines all of these attributes in an affordable package but progress is being made. Here we introduce three new torches from the LED Lenser range that we have heard great things about and one new lamp and two new torches from Cluson.
LED Lenser P7.2
The LED Lenser P7.2 is a hugely popular, general purpose handheld LED torch. Despite its compact size (it weighs just 175g!) it is very powerful, boasting 320 lumens when used at its highest setting. It has a robust but ergonomically designed weatherproof casing (IPX4 rating) and is great for prolonged use in the field. At the high setting (320 lumens, 260m beam) four good AAA batteries will last for two hours and at the lowest power setting (40 lumens, 100m beam) the batteries will last for 50 hours.
The LED Lenser P17.2 has a higher specification than the LED Lenser P7.2 with a powerful beam of 450 lumens that can reach 420m. It is constructed from tough, aircraft-grade aluminium with a dust and water resistant coating (IPX54 rating) and a smart, anti-slip black matte finish. The P17.2 has a fast focusing mechanism which enables the use of one hand to hold the torch and focus the beam simultaneously. Power, Low Power and Boost modes can be selected using a large dynamic switch that is designed for single handed use and for users wearing gloves. Perfect for carrying out newt surveys. Three D-cell alkaline batteries will power the P17.2 for 300 hours at the lowest setting (50 lumens, 140m beam) and for an impressive 30 hours on the highest setting (450 lumens, 420m beam).
We have also added the LED Lenser H7.2 Head Torch – a great little head torch with an extremely powerful 250 lumen maximum beam. Its lightweight (165g) and clever design make this torch extremely comfortable to wear and easy to use. Choose between eight light functions ranging from the most powerful 250 lumen, 160m beam setting to a comfortable 20 lumen setting for reading and note taking. Four good quality AAA batteries will power this head torch for seven hours on the maximum setting and for 60 hours on the lowest setting.
Cluson CB3 LED
The Cluson CB3 LED Lamp combines the legendary features of the CB1 and CB2 High-Power Lamps with an LED lighting system. The 25W bulb uses half the power of the 50W Xenon bulb in the CB2 and produces an impressive 750m beam and four hours of continuous illumination (compared with just 1.5 hours for the CB2). For those of you that already own a CB2 the great thing is that you can buy the new lamp head on its own – more than doubling the performance of your old CB2 for a fraction of the cost of a new lamp.
The RE1T Red Eye and the Pro Scanner ML1000 Torches from Cluson use the same aircraft grade alloy body and rechargeable Lithium-ion batteries to produce two lightweight (190g) and robust torches that are perfect for surveys. The RE1T includes a red CREE LED giving a 300m beam of red light for two hours on the high power setting (10 hours on low power) and would be great for spotting badgers. The ML1000 also uses a CREE LED to produce a 300m beam of intense white light (1000 lumens), perfect for newt surveys although the battery life at full power is fairly short at 1¼ hours (three hours at low power). One set of Lithium-ion batteries and a charger are included, spare batteries can be bought separately.
Installing a camera into a bird box is a great way to keep an eye on the nesting birds in your garden. Image by Simone Webber.
Deciding which nest box camera to choose involves a complicated tiptoe through competing technologies and equipment. Before you start watching birds you have to decide what sort of system is best for you and, crucially, how much money to spend.
The first question you need to consider is whether to choose a wired or wireless system.
Wired systems have a cable running from the nest box back to your house or classroom, which carries both power and the television signal. This results in excellent image quality but may not be ideal if you have children or pets in your garden, or if a cable running to your bird box will interfere with the gardening. You will also need to feed the cable into your house, either by drilling a hole in the wall or by feeding it through an open window.
Wireless systems do not require a cable to run between the bird box and the television but instead transmit images to a small receiver situated inside the house. However, a power supply will still be required for the camera (i.e. from a shed or outbuilding) and the signal can be compromised by other wireless devices in the area or by trees and other structures between the nest box and the house.
Next you will need to consider whether you require a complete kit or just the camera.
If you are new to this particular aspect of watching and listening to birds, a complete kit, such as the Nest Box Camera Starter Kit is a good and economical choice. This starter kit includes a bird box with a camera mounted in the roof, which provides colour footage during the day and black and white at night. A 30 metre cable plugs into your television and supplies the camera with power. Another option is the Gardenature Nest Box Camera System, which includes a bespoke red cedar nest box made to RSPB and BTO guidelines. A small sliding drawer at the top of the box houses the Sony CCD camera, which adjusts automatically depending on light levels. A 30 metre cable connects the camera to your television.
For the handyman or woman who wants to put a system together themselves, either in a bespoke or existing nest box, the Nest Box Camera with Night Vision is a good choice. The tiny camera will focus from a few centimetres to roughly 30 metres, with high definition for excellent daytime and night time images. The camera comes with a 30 metre cable and extension cables are available to purchase separately. The Wireless Nest Box Camera Kit is a great option if you want to fit a wireless camera to your own bird box.
What about watching on your computer?
All of the cameras and kits that we sell come with either a cable or wireless receiver that will connect directly to your television. If you want to view or save your footage onto your computer then an additional USB capture device is required. These are available both for Windows and Mac operating systems and come with all the software you require to get started.
Five new bat detectors will become available in 2016 – two new models in the Song Meter family of bat detectors from Wildlife Acoustics, two new passive detectors from the Swiss manufacturer Elekon and the long anticipated Anabat Walkabout. Here we will give you a quick round-up of the key features of each new detector along with news of several detectors which will no longer be available. We will also introduce an exciting new BatCounter and camera trigger.
The SM4BAT is available in a full spectrum or zero crossing version.
Wildlife Acoustics have brought out a new detector aimed squarely at the consultancy market – the SM4BAT. The SM4BAT is available in two versions – full spectrum (SM4BAT FS) and zero crossing (SM4BAT ZC). Both come in the same dark green plastic case (a bit like a Bushnell Natureview Trail Camera) which is weatherproof, slightly smaller and lighter than the SM2BAT+ and can be padlocked shut to prevent anyone tampering with the detector. Both use the SMM-U1 microphone which was designed originally for sale with the SM3BAT detector. They are also programmable and will record on a single channel for around 30 nights using four D-cell batteries.
Wildlife Acoustics have also announced that they are phasing out the EM3+ and the SMZC, which are being replaced by the Echo Meter Touch and the SM4BAT ZC respectively.
The Batlogger C (left) and Batlogger A (right) offer solutions for a variety of bat survey situations.
Elekon have released two new passive detectors within the last few months which are based around the very highly regarded Batlogger M handheld detector. The Batlogger C is probably the highest specification bat detector on the market – it has everything you would expect from a high end passive detector including programmable recording schedules, fully weatherproof enclosure, and high quality full spectrum recordings as well as many extras. These include optional sms and/or email messages reporting the status of the unit and the number of recordings made as well as the amount of power remaining. Furthermore, because the Batlogger C also has in-built GPS it can send you an alert if the unit is moved. A wide range of power options are available: a 50 hour rechargeable battery is included and there is space for a second. Mains power is also an option as is solar power which requires the addition of the Batlogger C solar panel. When used with two 50 hour batteries, just half a day of sun in every 10 days should be enough to keep the Batlogger C powered indefinitely.
Also from Elekon, the Batlogger A is a miniaturised passive detector. It is programmable and will record for up to 30 hours on eight AA batteries (e.g. three 10 hour nights). The Batlogger A is housed within a small weatherproof enclosure and includes a Knowles FG microphone on a 2m extension cable.
The Android based Anabat Walkabout allows you to view live sonograms in the field.
The Anabat Walkabout, a handheld detector for transects and roost emergence surveys is also expected for the 2016 season. This touch screen Android tablet based detector not only records any passing bats but also lets you view the sonogram in real time in both full spectrum and zero crossing formats. A GPS, lux-meter, thermometer and humidity sensor are all in-built so not only will each call be geo-tagged but you will also be able to collect the full range of environmental data for each transect without needing any additional tools. A fully charged unit will last for around 8 hours.
The BatCounter will log the number of bats passing through as well as the direction of their movement.
The BatCounter has the potential to be a very useful tool for both researchers and consultants. It uses a network of infrared beams to count, and log the direction of movement of bats moving through a detection area of 76 x 35cm (standard model) or 36 x 35cm (tree model). It has a GSM function that can send daily reports via text or email and will run for three days on eight AA batteries or for much longer periods using a 12V battery. You can also connect a Nikon or Canon DSLR camera and take pictures of the bats as they pass through the Batcounter.
UPDATE 7th MARCH 2016 – The Bat Survey Training Course has now been cancelled.
The use of passive monitoring to assess bat activity has important implications for how we work with the vast amounts of accumulated data, and automation now plays a crucial role in dealing with datasets which often contain thousands of recordings.
This bat survey training course has been designed to give you insights into the how-to of passive acoustic bat detection and call analysis, including its pitfalls. It will give you the skills to conduct passive acoustic bat surveys with confidence and to analyse your results in the most efficient and accurate way.
Topics covered will include: Why and where do we listen for bats, how to detect bats, signal analysis, bat call identification and working with large datasets. It will also include a short introduction to the Batcorder system.
It will involve a combination of classroom-based learning and fieldwork and will be led by Volker Runkel from the German company ecoObs, manufacturers of the Batcorder system.
The new SM4BAT range of passive bat detectors from Wildlife Acoustics was announced at the 2015 Bat Conservation Trust AGM.
The Full Spectrum (FS) version will allow you to record bat calls in 16-bit resolution at a sample rate of up to 500kHz on a single channel. The Zero Crossing (ZC) version is also single channel and will record zero crossing files. Both are weatherproof, come with a three year warranty and will record for up to 30 (10 hour) nights when powered with four high quality d-cell batteries.
The Great Green Bush Cricket is the largest of the UK Bush Crickets. This beautiful image of a female cricket was taken by Charlie Jackson, from Flickr Creative Commons (CC by 2.0).
The order Orthoptera consists of the grasshoppers and crickets. Although most suited to warmer climates where they are incredibly diverse, in Britain we have 27 native species, as well as a number of non-native, naturalised species. From a very young age we are aware of these beautiful creatures as the sounds they produce fill our countryside with noise.
The characteristic Orthoptera song or “stridulation” is produced either by rubbing the wings together (observed in most of the grasshoppers) or by rubbing a hind leg against a wing (a method used by most crickets). The sound produced is an important part of the courtship ritual and is also used for other types of communication. As the sound created by different species varies significantly, studying these calls is an excellent way of surveying Orthoptera, and is helpful for finding individuals which can then be identified visually.
Stridulation produces a sound which covers a variety of frequencies – the sound made by grasshoppers is usually audible, but many species of cricket produce a higher ultrasonic frequency which cannot be heard by most humans. The use of a bat detector to listen to these higher frequency songs is an excellent way to listen to those species that we would not ordinarily be able to hear, such as the Speckled Bush Cricket. It also allows us to increase the range at which we can hear the audible ones. Bat detectors are also of use to older surveyors, whose ability to hear higher frequencies has naturally declined.
A simple heterodyne detector is perfect for listening to grasshoppers and crickets – one such as the Magenta Bat 4 or the Batbox IIID is ideal as it allows you to tune it to a specific frequency (as opposed to some of the more “intelligent” detectors which will alter it for you). The detector should be set to a frequency of 35-40kHz then all you need to do is sweep it around in different directions until you pick up your subject. It is best to stand in one place while surveying as the noise produced by your footsteps and clothes moving will produce background ultrasound noise which can confuse what you are hearing. The best days for surveying are warm and sunny; crickets are generally crepuscular (active during twilight) whilst grasshoppers are usually active throughout the day.
Unlike bat detecting, where the peak frequency is a key diagnostic feature for determining species, this information is less important for Opthoptera. Of more importance is the pattern and type of sound produced. The Environmental Records Centre of Cornwall and Scilly has a great guide to identifying Orthoptera including a useful information sheet on the use of bat detectors. They also have a collection of sound files of grasshoppers and crickets that you can use to recognise the typical calls produced by many of the species found in Britain.
