The Appeal of Using Song Meters
With recent advances in digital-signal processing and bat detector technology, Dr. Stuart Newson, from the British Ornithological Trust (BTO), realised more could be done. In April 2013, Dr. Newson and some colleagues from the BTO decided to engage members of the public to participate in large area bat surveys and take advantage of bat-recording technology that would not normally be available to them. With appropriate guidance, passive detectors such as Wildlife Acoustics' Song Meter, recording in full spectrum, could be deployed in the field by anyone interested in getting involved in monitoring his or her local wildlife. From here, the Norfolk Bat Survey was born (www.batsurvey.org). Startup funding came from the People's Trust for Endangered Species (PTES) and Natural England (Defra Fund for Biodiversity Recording in the Voluntary Sector), but many other organizations have since supported the survey efforts.
Explained Dr. Newson, "I set this this project up to address what I saw as a barrier for achieving large-scale volunteer-based monitoring of bats. But most importantly, I did this because I thought it would be fun to combine a personal free-time interest in bats and my work in designing and analysing data from large volunteer-based surveys. I realised that there was a huge pool of potential volunteers who would be interested in finding out more about bats, if given an opportunity to borrow equipment to find out what was in their local area."
How It Works
Volunteers sign up and borrow a passive bat recorder from one of 21 centres hosting equipment. Dr. Newson has collaborated with a wide range of communities and organisations that already had their own network of volunteers or members, and in doing so opened up citizen science to a new set of people. Volunteers leave the detector outside at three different locations over three nights within a 1-km square. Bat calls are recorded and saved to a memory card. After three days, volunteers return the detector and mail the memory card containing bat recordings to the BTO. The data are analysed using software to help assign bat calls to species.
Dr. Newson explains, "I measure success in relation to the number of volunteers involved in the project and the number of 1-km squares surveyed for bats. For example, we have seen a year on year increase in the number of people taking part and in survey coverage, which demonstrates to me that the project is working." Volunteers are then sent a report with the results of their survey within a few days of taking part. The Norfolk Bat Survey demonstrates the cost-effectiveness of setting up a network of centres across a survey area of interest from which anyone can borrow a passive detector for a few days.
The Role of Song Meter Detector/Recorders
Before starting the Norfolk Bat Survey, Dr. Newson had access to a Wildlife Acoustics Song Meter which he was able to purchase thanks to a British Ecological Society (BES) Small Project Grant. With a small number of recorders borrowed on weekends from a friendly environmental consultant, Dr. Newson compared several detectors from different manufacturers, to consider the value of full-spectrum versus zero-crossing and to experiment with various software options. Dr. Newson decided on recording in full-spectrum in order to obtain as much information as possible from the recordings, and use call measurements in further analyses to species identification. Of full-spectrum passive detectors available in 2013, the Wildlife Acoustics Song Meter was the most affordable option, and price was the main reason for choosing this recorder for the Norfolk project.
Dr. Newson explains, "Personally, I like the SM2BAT+. It is not perfect and hasn't been without its issues, but it has done a good job for our project, and we are still using the same detectors after three seasons. We are looking forward very much now to seeing the new SM4BAT FS, which offers everything that we need in a passive recorder, with some big improvements over the SM2BAT+ that we have been using."
Results to Date
Norfolk, UK is a large county with an area of 5,371 km2. Over time Dr. Newson and his colleagues improved local knowledge and interest in bats and enlisted over 800 volunteers. Since the start of the project in 2013, volunteers have surveyed 1,146 1-km squares (>20% of Norfolk). This has generated over 1.2 million bat recordings, making this one of the most extensive high-quality datasets for bats collected by citizen scientists from anywhere in the world.
At a local scale, the Norfolk project has improved understanding of patterns of occurrence and activity of all species, from the near ubiquitous Common Pipistrelle Pipistrellus pipistrellus to the locally scarce Leisler's bat Nyctalus leisleri (Newson et al. 2015). Common pipistrelle and Soprano pipistrelle were by far the most commonly recorded bat species. Across 2013 and 2014, these two species made up about 93% of all bat recordings (492,292 recordings). In contrast Nathusius' pipistrelle (see below) made up about 0.2% of recordings (919 recordings).
Advice for Deploying Song Meters and Analysing Data
First, Dr. Newson would advise someone considering a similar Citizen Science project to find a fixer / technical adviser. Joe Rayner has worked with Dr. Newson to find practical solutions to any problem that the Norfolk Bat Survey encountered, including designing microphone holders and poles for raising the microphone up into the bats flyway. Mr. Rayner also assists in preparing and testing each Song Meter kit as it comes in and then is refurbished to go back out.
Dr. Newson has four additional pieces of advice:
- Think very carefully when choosing between full-spectrum and zero-crossing, noting that it is straightforward to convert FS to ZC, but not vice versa.
- Cost into the development of the project the web systems through which volunteers can sign up and book the detectors, rather than trying to find a solution to this later. Publicity can direct people to an online sign-up tool, showing survey coverage, available squares and enabling volunteers to sign-up. Such a system allows uptake to be monitored during the project, and if there are particular areas where uptake is slow, promotion can be targeted to these.
- A system should be set up as part of the project, where you are able to provide rapid feedback on species recorded by participating volunteers, ideally within a few days of recording. This keeps the volunteers engaged showing feedback from their effort.
- Consider different funding models. The Norfolk Bat Survey needs different funding sources to make the bat project sustainable in the longer term – perhaps potentially looking for business sponsorship to cover the on-going cost of repair and replacement of equipment, or where volunteers pay to take part.
For the future of the Norfolk Bat Survey Project, Dr. Newson would like to have a centralised system for analyses. He wants to archive all original raw recordings as this data may be useful for future questions. Engaging more with the community, data could also be put on a website where volunteers will be able to visualise their results in relation to others.
Given funding, Dr. Newson will continue the Norfolk Bat Survey in the long-term, but new plans now include the setting up of a much larger acoustic bat project across southern Scotland, in partnership with the Bat Conservation Trust, National Trust for Scotland and funded by Scottish Natural Heritage. For this he opted again to use the Song Meters.
More broadly, the bat detectors are often recording more than just bats. There is clearly an exciting opportunity for "bat recordings" to contribute more widely to biological recording in the future. For example, there are over 300,000 recordings of bush-crickets from Norfolk surveys. As a result, Dr. Newson is currently collaborating with colleagues at the Muséum National d'Histoire Naturelle in Paris to help test and feed into the development of software for the acoustic identification of bush-crickets.
Thanks to Stewart Newson and his collabortion on the case study as well as the Norfolk Bat Survey which provided the majority of the content for this case study.