Since 2013, volunteer citizen scientists taking part in the Norfolk Bat Survey have 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.
In this case study for the Citizen Science and Acoustic Monitoring groups, Stuart Newson explains why the project was set up, the challenges it aimed to address and looks forward to the future of the project.
Having a personal interest in bats, the Norfolk Bat Survey was originally set up with colleagues at the British Trust for Ornithology (BTO) as a bit of fun, whilst improving local knowledge and interest in bats, but has since enlisted over 800 volunteers. Volunteers sign up and borrow a passive bat-detector (Wildlife Acoustics SM2Bat+ recording in full-spectrum) from one of 21 centres hosting equipment. Leaving 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 post the memory card containing bat recordings to the BTO. The data are analysed using software and additional step that help assign bat calls to species (described in more detail in www.batsurvey.org/species-identification) and volunteers are sent a report with the results of their survey within a few days of taking part.
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 our 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). This has demonstrated 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. Through our choice of centres, it has given us the opportunity to work 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.
I am extremely fortunate to work for the BTO which is an independent charitable research organisation which specialises in citizen science and the study of UK bird populations, but has a growing reputation for work on other taxonomic groups. Most of my work at the BTO has been reliant on input from volunteers, who contribute a huge amount of time and skill to undertake a wide range of structured and complementary surveys. These data provide long-term information that has so essential for tracking and understanding change in UK wildlife populations.
The problem we were trying to solve
In the UK, the monitoring of bats in undertaken on a large scale through the National Bat Monitoring Programme (NBMP) run by the Bat Conservation Trust. Established in 1996, this long-term monitoring programme relies upon trained volunteers to help provide robust population trends for 11 of the UK’s 17 breeding bat species. These volunteers take part in various types of survey, including bat counts at winter and summer roosts, as well as standardised bat-detector surveys using simple, tuneable detectors (heterodyne detectors) that allow identification in the field. The bat-detector surveys focus on specific, relatively easily identifiable species and the survey methods are designed to be as inclusive as possible, using affordable bat-detectors to maximise participation and geographical coverage.
There are, however, limitations to this bat detector approach, as not all bat species are easily monitored through these methods. There are a number of reasons for this, including the difficulty of distinguishing the calls of some species, the expertise that is required to do so, the expense of bat detectors that can make high quality sound recordings, and the time-consuming process of analysing sound files containing bats.
However, recent advances in bat detector technology and digital-signal processing, I realised than more can now be done. The technology now means that it is possible to collect large volumes of high-quality acoustic data and software for semi-automating the analysis of sound files. Used within a well-designed structured monitoring programme, it was clear that this has the potential to provide robust and representative assessments of species for which in the UK, we have a legislative and reporting requirements. Unfortunately, the equipment required for these purposes has been expensive, so in the UK, its use has been largely restricted to use by environmental consultants and university research groups.
The aim of the Norfolk Bat Survey was to trial a way of enabling members of the public over a large area to participate in bat surveys and take advantage of bat-recording technology that would not normally be available to them. We felt that with appropriate guidance, static detectors recording in full spectrum could be deployed in the field by anyone interested in getting involved in monitoring his or her local wildlife.
Where our funding came from
We are extremely grateful to the People’s Trust for Endangered Species (PTES) and Natural England (Defra Fund for Biodiversity Recording in the Voluntary Sector) for providing start-up funding for this project. Since this time, we have extended the project a little with some additional bat detectors funded by the Norfolk Biodiversity Information Service, the Norfolk Biodiversity Partnership, the Geoffrey Watling Charity and the Love the Broads fund, and Essex and Suffolk Water Branch Out Fund helped fund our development of an online system for reserving bat detectors. Initial development of the project was largely worked on in my evenings, which I probably wouldn’t recommend, but the project now has a survey organiser, Hazel Evans who works with volunteers and processes the recordings as they come in.
What we plan to do next
Given funding, I would to 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 to run from May 2016.
More broadly, with bat detectors recording more than just bats (e.g. >300,000 recordings of bush-crickets from Norfolk), there is clearly an exciting opportunity for “bat recording” to contribute more widely to biological recording in the future. I am currently collaborating with 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, for which work is on-going.
In terms of a wish list, there are several areas where if we had more capacity we would like to develop, and are potential areas for developing collaborations. To just pick out two areas, the first relates to the analytical challenge of trying to estimate abundance when individual identification is not possible. No published studies have so far attempted to estimate the population size for bats from large-scale acoustic monitoring data. The problem is that it is not possible to individually identify bats, and that an individual bat can trigger a detector to record more than once, generating clusters of records. In theory this could be addressed using one or two analytical approaches:
- An extension of occupancy modelling for mammal track data, where individual identification is not possible (Guillera-Arroita 2011. JABES);
- Extensions to random encounter models, originally developed for camera-trap data but recently adapted for acoustic monitoring applications (Lucas et al. 2015. MEE).
Cracking this problem will increase the value of such data and monitoring approach of using passive detectors, as well as having important implications for evaluating the status of bats in the UK, where current estimates of population size are based on guesswork. I have some time to work on this this year, but I am open to ideas from statisticians for developing work in this area.
The second relates to the acoustic identification of birds. Bat recording has the potential to also provide monitoring data for particular groups of birds, such as nocturnal birds and birds in remote for example upland habitats which are currently poorly monitored in the UK. We know that we have already collected >80,000 bird recordings through the Norfolk Bat Survey, and we would like to evaluate the potential of these data. We would be keen to hear from anyone in the community who is already working on the acoustic identification of birds, and where a dataset of unknown bird recordings would be helpful for building or testing models.
About the Author
Stuart Newson is a Senior Research Ecologist - Population Ecology and Modelling Research with the British Trust for Ornithology (BTO). In this role he is mainly involved in the survey design and analyses of data from large national volunteer-based surveys and demographic data on wild bird and mammal populations. He has a particular interest in bats and in large-scale acoustic monitoring of biodiversity. Get in touch with Stuart through his profile.
Collaborate with Stuart in the Acoustic Monitoring group.