Test your mic and avoid a wasted session.

by Peter Flory, Peersonic Limited 

It makes sense to test your bat recorder or bat detector equipment prior to use. Microphones can degrade with time, the main enemy being humidity, or worse still total saturation.

So far, I have found that over a 5 year period I have no customers with failed microphones where they are using handheld equipment. I am sure they are all still working fine, but worry that they might be degrading and the user is unaware.

Static equipment left out in the weather is a different matter. I have observed totally dead mic's, and again more concerning some that have started to lose the top end response after a year or so of use.

So here are some thoughts on how to test your equipment and be sure it is going to be effective, with cost in mind.

Jangling Keys:

If you are a casual user why not just jangle keys. A detector will give you a response, but you just don't know how well it is operating over the frequency range.

Jangling keys is better if you have a recorder, the stimulus can be recorded and the response viewed as a spectrogram.

Here is a spectrogram of key jangling,I tried with different bunches of keys and found that on the whole the stimulus was covering the spectrum well up to about 110 kHz. Although it is not a repeatable signal. 

Fixed Frequency or frequency sweep:

A better test would be to use a definite fixed frequency, generated from a signal generator, a specific sine wave , or series of waves played back through a tweeter can give a measurable stimulus. 

Use a sine wave rather than a square wave as the latter contains many harmonics and it would be nice to observe the response at each frequency step as far as possible.

Signal generators are standard electronic test equipment. They are usually around the £150-£200 area, but there are some lower cost kits too that might be as low as £50.

A low cost China manufactured sig gen at a bit less than £150.

Next you need to select a speaker/ tweeter. These are never designed to cover the full bat spectrum, so some trials and selections are required. However they are not costly. There are voice coil speakers which are fairly level over 20kHz to 90kHz, Or pietzo speakers that will go much higher, both will suffer from features over the band so this needs to be considered. - There is no perfect flat response.

Now it is possible to chose a selection of signals, at predefinied amplitude ( volume ) and set up your own regular test pattern.

Just test and record, and observe and trends in the recordings that suggest deterioration over time.

Monthly perhaps.

Calibration:

Having found that a microphone is deteriorating, typically at the higher frequencies. You might want to calibrate it. You can't.

A mic that is on the way out is best consigned to the dustbin. This should not be confused with the process of matching a mic to a recorder by equalisation. That is fine, but not a great idea if the mic is becoming unreliable.

What to do with a sick mic:

Manufacturers vary, if you are able to replace the internal mic element this should be cheap, if the mic is a unit, you will need complete replacement. So from the lower end ( replacing the insert) to replacing the unit, the cost would be anything from £12.00 to about £300.

Specific bat Ultrasound mic testers:

Rather than go for a test equipment based arrangement, you could do better by obtaining an ultrasonic mic tester as a unit, speaker included or integrated, with features specified in the suppliers data sheet or users manual. Should make life easier.

Some testers emit a spot frequency, 40 kHz, 60 kHz. This will certainly show something, but what about at 125kHz? Or the various points in between? Best thing then is to emit a series of stepped frequencies. Also a chirrup is useful as it gives a fast changing signal and your spectrogram will show up some missing points perhaps.

Stepped frequencies will allow you to check your heterodyne or FD equipment at each point, a full range of patterns is even more revealing for recording FS gear.

At Peersonic I have developed a tester that emits single steps over the range, plus patterns, and for fun some emulated familiar bat sounds.

https://www.peersonic.co.uk/playback

Speaking to my competitors I find there are fixed frequency testers, and I note the Titley "chirp" equipment, which is similar , but moves on to offer a complete test bench that ensures the speaker and receiver are at a fixed distance from each other.

From left to right: a Peersonic multi-mode mic tester, an Elekon dual-mode tester and a Titley Anabat tester 

Test Environment:

If you are expecting to get highly repeatable calibrated measurements you had better hire a sound chamber, and probably some expensive transducer equipment. But, just testing if it's ok is really good enough for most of us. Here is some advice -

Try to keep the following the same each time for best results.

Use the same room.

Try to ensure that the furniture is in much the same position each time.

Do not stand next to the speaker, or in front, best to operate from behind the setup..

Avoid wearing wooly pullovers as they are absorbers of sound.

If you can, check that there is no electromagnetic interference, (a desktop PC with the sides off tends to transmit all sorts of rubbish).

Or test outside in an open space.

Conclusion:

Testing your mic is a bit like backing up your computer. Unless you are running a schedule, it really only happens when its too late.

Partnership for Biodiversity in Planning - Wildlife Assessment Check

by Rosalie Callway (BCT's Partnership for Biodiversity in Planning Project Officer)

Since 1970 many UK wildlife species have been in decline, with over 1,200 species now extinct or threatened with extinction (State of nature report, 2016).  One of the factors that has caused this decline is land use changes from urban development.

Smaller developers may be unaware that it is a statutory requirement for UK local planning authorities to consider the ecological impact of developments via planning applications, as well as promote a positive contribution to biodiversity. 

However, some authorities are struggling to find the resources to conduct the necessary checks to see if wildlife may be impacted by a proposed development. Without the right data about the biodiversity impacts, an authority can’t make an informed decision on planning applications – this means that authorities may be granting planning permission to developments that will have negative impacts to wildlife.

The Association of Local Government Ecologists estimates that two-thirds of local authorities do not have an in-house ecologist or ecology team. Restricted local authority budgets and lack of in-house ecological expertise means that biodiversity is given insufficient attention during the planning process. For example, in London, there were over 90,000 planning applications in 2016 but less than one percent (0.86%) of these applications consulted existing biodiversity data records to assess the potential impact of the applications (GIGL, 2017). This is despite the GLA estimating that around a fifth of planning applications (18%) are likely to require background biodiversity checks. In Hampshire, of 10,400 applications in 2017, only 4% (368) were checked by the local environmental records centre. Similar to London, Hampshire-based record centres had flagged a fifth of the applications (2,325) as of potential ecological concern.

The Partnership for Biodiversity in Planning is seeking to increase awareness about the need for background biodiversity checks, by local planning authorities as well as by householders and developers. The partnership, involving 18 organisations, has developed an online tool – the Wildlife Assessment Check – to help indicate when expert ecological input is required as a part of a planning application.

The Wildlife Assessment Check is a free online tool, designed to help householders and smaller developers check whether their proposed site and works are likely to require expert ecological advice before making a planning application. It aims to smooth out the planning application process for applicants by encouraging them to address potential ecological impacts early on, reducing unnecessary delays and costs. It also aims to support local planning authorities who lack in-house ecological capacity by encouraging applicants to take responsibility in addressing ecological considerations. 

The partnership is now rolling out the tool and inviting user feedback over the next few months to ensure that it works well and is straight forward to use.

Twitter: @BiodiversityPs 

Email: pbp@bats.org.uk            

Website: www.biodiversityinplanning.org 

The Pulling Power of Images in Bat Conservation

by Paul Colley

I’m a conservationist by instinct, because I love the natural world. But like many I now worry seriously about climate change, loss of habitat; you know the issues as well as I do.

We can all make a difference. As a photographer I’m naturally interested in the pulling power of good images in conservation. I’m really an underwater photographer by trade and have photographed so many interesting subjects, from trout and grayling in Hampshire chalk streams to blue sharks off the coast of Cornwall and silky sharks in Cuba.

Looking for a new challenge, I saw bats hunting over water whilst photographing trout and thought there was scope to do something different. I could not have found a harder target! The problem rightly started with the bats’ protected status and early in my research I contacted the Bat Conservation Trust and started a helpful dialogue about my project with people there and at Natural England. Although the chosen approach did not require a licence, I inevitably ended up with self-imposed restrictions, principally about levels of artificial light.

The lovely Daubenton's bat (Myotis daubentonii) has that super-cool trick of intercepting an insect just as it hatches at the water’s surface. But I also wanted to show the bat’s hunting flightpath and habitat. The technical challenges soon kicked in. I developed two techniques that were gentle on the bats. Low light (flash guns at minimum power) and infrared (almost invisible to human and bat eyes). Infrared opened up new creative possibilities and I used a constant light, flash guns and cameras all modified to specific infrared wavelengths.

You need millisecond precision to catch the action so I opted for a laser trigger with the beam riding a couple of centimetres above the water. My route to success was littered with a thousand failures, because making this work in the dark was tricky. Not least because I had to power the infrared lights with 240 volts using a 12 volt car battery and inverter, all mounted on tripods over water. It was an interesting risk assessment!

But persistence pays off. I might have given up one night when I stood waist deep in water for almost five hours. The bats were swarming around me chasing a massive hatch of insects. But not a single picture was useable. Utterly dejected, I discovered in the analysis next morning that I had made a silly mathematical error in my trigger calculations.

After fourteen months, over a hundred night field trips and countless other hours modifying the camera trap in my workshop, it came together in a beautiful image. I call it ‘contrails at dawn’ and it won the British Wildlife Photography Awards 2018 (you can see the image here: https://www.bwpawards.org/winners2018). The Bat Conservation Trust is already using it to draw people in to the bat conservation story.

So now I have a request for bat conservationists. Where can I go to document different species and the wider stories behind bat conservation? It must start with powerful imagery of the bats themselves, because that is what will hook people in. I now have an excellent suite of new photography techniques to exploit, but remain open minded about new potential subjects and stories. I’m keen to get involved with people who already hold the appropriate licences. If you would like to work with me in my quest to raise the conservation profile of bats by using powerful imagery, please do get in touch and offer me some suggestions. I cannot promise to work with everyone due to my busy programme. But I’m determined to work with some who might help me create good stories enhanced by the pulling power of new imagery.

Use the contact page at www.mpcolley.com

The MSP’s championing our bats - The Species Champions Initiative 100 day challenge

by Liz Ferrell, BCT's Scottish Officer

I am always a bit apprehensive before bat walks as there is always the weather to contend with in Scotland! But, it has to be said, bats have never disappointed me. They are hardy little mammals and they put on a good display for us as we walked around Holyrood Park in Edinburgh. Perhaps they enjoy the big occasions and Tuesday night was definitely one of those!

Through the Scottish Environment LINK, member organisations (which includes the Bat Conservation Trust (BCT)) were asking over 100 Members of the Scottish Parliament (MSP), who had accepted to become a Species Champion, to participate in a series of actions over a 100 day period (#Species100). We were asking them to help raise awareness about their selected species, the threats to their populations as well as the wider biodiversity concerns in Scotland. 

Taking part in the bat walk as part of this challenge were MSP’s Annie Wells, Finlay Carson and Fulton MacGregor who all attended on what was a wet and windy night at Holyrood. It needed more than rain to dampen their spirits however and it was lovely to chat to them about bats as well as their work as MSP’s. 

All excited to start our bat walk outside the Scottish Parliament 

I am happy to say that their smiles remained there for the remainder of the night! Annie was very pleased to have her species, the common pipistrelle, foraging over her head and we watched as the bat continued to fly back and forth. The poor thing was fighting against the wind and we all agreed that he or she was a determined individual!

Finlay was as keen as ever, even without the opportunity to see or hear his species, the Leisler’s bat. He is very passionate about his chosen species which is found in his constituency of Galloway. He has visited the Wood of Cree where these rare bats are fairly common. Fulton too has still to see his species, the natterer’s bat, and without visiting a roost (which I have promised him) it is a tall order! They are not as easy to find as our pipistrelle species are. But, he knows a lot about his species already and I have run a bat walk for him in his local constituency in August.

Reflecting back on this 100 day challenge, I have to say it has been great. It was such a pleasure to see how genuinely enthusiastic our MSP’s all are about their species and to see that they know so much already about bats! It has certainly kick started my engagement with them and I am really looking forward to working with them all going forward as we organize some more batty evenings. I hope I will have further news to share with you on this initiative soon…

LINK’s award-winning initiative “Species Champions” pairs MSPs with species that are under threat in Scotland. With almost 1 in 10 species in Scotland at risk of extinction, political support for protecting our precious natural environment has never been more critical. To find out more about this initiative check the Scottish Environment LINK’s website here. 

‘Testing Times Ahead – A Cosmic Bat Adventure’

Beverley Clarke, of the Loch Lomond Bat Group (LLBG), explains about a big leap the small group have made this year. 

So, what did you do on the very hot and sunny May Bank Holiday Weekend? (Apologies to those of you in England who were subject to flash flooding). Well, here in Scotland, where summer conditions are a rarity to be savoured, most Scots were making the most of the tropical like conditions - having a barbecue or garden party, going for a picnic, visit to the beach or camping. However, for some Loch

Lomond Bat Group members it was to be a hot and sticky venture into their first BCT/Forest Research ‘Putting UK Woodland Bats on the Map’ survey (PUKWBotM). Loch Lomond Bat Group are a very small hardy bunch of bat enthusiasts.  We have a core membership of just five or six people at any given point, who start each survey season with the hope that they will at least make it through our NBMP surveys and public events programme.  Every year we endeavour to recruit some more hardy souls to join us, but usually by the time we get to Field Survey time, we are back to the Famous Five!

Liz Ferrell helps with set up of SM2

So, it was quite a leap into the unknown for our wee bunch to take something of the magnitude of PUKWBotM.  For context, we have likened it to a classroom full of kids making water bottle rockets in one week and sending one of their pupils to the moon on another week!! Maybe a slight over exaggeration, but when the Scottish Bat Officer Liz Ferrell organised the first training night to help familiarise us with the equipment we would using in the survey, that is what the learning curve felt like.

In brief, for those that may not be aware, the survey involves the of testing three types of bat field monitoring equipment – standard SM2 detectors, low cost acoustic sensors called Audio Moths, and Pettersson Ultrasound Microphones (which connect to tablets).  As well as setting out the static recording points, there is also a walking transect. The final aim is to gather data that can be used to calculate representative detection probabilities for different bat species in woodland, to inform the design of future woodland monitoring schemes.

Adam and Gavin trying to set up an SM2

The two members who gleefully signed us up for the project last year, had to design the transect themselves in two types of woodland; broadleaf and plantation. This they dutifully did last year, and this year were sent through all the gadgets and gizmos, with our key member, Adam, signing his life away to a few thousand pounds worth of BCT equipment.

We now had our ‘rockets’ to play with but had little idea how to launch them despite the extensive manuals and ‘idiot guides’ sent through by the Woodland Officer, Sonia Reveley from London. This is where the amazing Liz Ferrell, the new Scottish Bat Officer stepped in. Through her experience, knowledge, sheer will, enthusiasm, Doodle Polls and some backside kicking, she helped those that signed up to get trained, set up the first dates for the surveys and helped us set up the equipment for the first survey on a sticky midge filled Saturday night in a broadleaf woodland in the Trossachs, after having driven directly from Wick from her holiday! By the Monday night for the plantation survey, we were on our own!  The mission to the moon had begun!

With the first month’s surveys done, we have another four to go. We have already hit a couple of meteorite-like snags on our mission, but we are still learning.  Maybe by the 3rd or 4th survey, we might make it all the way there!

We are very proud, if a little foolish, to be the only bat group in Scotland attempting this survey, but if we can pull it off, it may seem like a small step for those bat conservationists out there, who do this on a regular basis, but for us it will be a great leap for little group of enthusiasts.
Finally, a huge thank you to Liz for her help, support and dedication to our group and for getting us to the launch pad in time….to infinity and…. right enough of that!!

Liz Ferrel and Suzie the guinea pig with trainees

An interview with a Helpline Out of Hours Volunteer

Rachael Varney is a Bat Helpline Out of Hours (OOH) volunteer, a service where volunteers answer emergency calls from the public who have found a bat in need of help. The OOH Bat Helpline is active in the evenings (5:30PM - 10:30PM) and on weekends and bank holidays (9AM - 10:30PM). 

What inspired you to volunteer on the national bat helpline out of hours service (OOH)?

I used to work as a veterinary receptionist and when injured or grounded bats were brought in to the surgery I would always have a quick peek at them in the box! Nobody seemed to know much about how to care for them, but luckily, we had a very knowledgeable bat carer who we would call upon to take them off our hands. When I saw the volunteer opportunity for OOH, I thought it would be great to learn more about bats, and hopefully do a little to help them too.

There are lots of wildlife you could have given your time to, why bats?

I think bats are misunderstood and somewhat shrouded in mystery, and many people dislike or even fear them. As well as wanting to learn more about bats myself, I hope I can educate people whilst doing the OOH call taking to realise what interesting creatures they really are.

What do you enjoy about volunteering on OOH?

I enjoy talking to different people from all over the UK – you never know who will be on the other end of the phone, or what situation the bat is in. Most people who have taken the time to call OOH, have a genuine desire to help the bat, even if they have a fear or are unsure of what to do. It’s great to be able to give people advice and the confidence to be able to help the bat – there’s a real feel-good factor involved. I enjoy learning about ways we can lessen our impact on the natural world and regularly get involved with online petitions on social media, but I sometimes feel overwhelmed by all the negativity. OOH has shown me that there are some really kind people who are willing to go out of their way to help, and that’s quite uplifting.

What’s your at-home set up like for OOH?

I make sure I have everything to hand -  some snacks, a couple of cold drinks, a notepad and pen, and my OOH folder given to me during training. I’m quite lucky to have a spare bedroom that acts as a little office, so I can concentrate on OOH without too many distractions, although I do sometimes end up with the cat sat on my knee!

Do you have a favourite or most satisfying call that you can share with us?

I think my favourite call so far was from a gentleman who had been out walking his dog on a park and had seen a bat trapped behind the mesh of a large disused speaker. Before calling OOH he had already contacted the places I was going to recommend – the RSPCA, the local council to see who the speakers belonged to, a security firm connected to the park. I was at a loss as to what to suggest, but put him in touch with a bat carer local to him, in the hope they might have come across a similar situation before and had some more ideas. I was hopeful, but really worried it would not be a happy ending for the bat.

After my Bat Watch, I spoke to my allocated Back up Staff (during Bat Watches,  volunteers always have a phone number available for a member of staff from the Bat Conservation Trust to provide advice or assistance, which is really reassuring). I decided to call the gentleman back just to double check we had discussed every possible avenue of people or places to call upon for help in trying to rescue the bat. I’m so glad I made that call as what he told me made my weekend! The RSPCA had managed to send out an inspector, and the bat carer who I put him in touch with had attended to help, along with the local fire brigade! They managed to saw through the speaker so that the bat carer was able to get close enough to get hold of the bat and safely contain him. It was a fantastic team effort from everyone involved to rescue this little pipistrelle bat, fondly named Boris by the man who spotted him. I have since heard that Boris had a little rest and recuperation that evening with the bat carer and was fit enough to be released the following evening.

How about your most challenging call so far?

So far, I’ve been quite lucky, and I’d say my most challenging call was from a lady who was struggling to hear me over the excited chattering of her young children who had just found a bat! I think it’s important that children take an interest in nature and advised the caller that the Bat Conservation Trust would happily send out some children’s activity packs, so they could learn more about bats.

What advice would you offer to anyone else considering taking up OOH volunteering next year?

Go for it! Although I come from an ‘animal background’ having worked in a veterinary practice, I knew hardly anything about bats.  The Bat Conservation Trust provide a day’s training which covers everything you need to know to get started on OOH call taking and offer great support for volunteers along the way. OOH volunteers are usually the first port of call for members of the public who have found a bat and are usually the ones who ‘get the ball rolling’ for a rescue / rehabilitation attempt. It feels great to be part of something so beneficial for British wildlife.   

We have to ask… favourite bat and why?

I’ve not seen one in real life (yet!), but it has to be the long-eared bat. Those ears are just too cute!

Twilight Bat Walks

by David Jackson from Mid Essex Hospital Services NHS Trust

In the United Kingdom we have 18 species of bat, all are insectivorous and a great environmental indicator. A single bat can eat up to 3000 midges in one night making them an excellent natural insect controller, but unfortunately over the last century their populations have declined, making each roost important for future survival. Due to their decline, bats and their roosts are protected under UK and European law with a roost defined as any place that a wild bat uses and is protected whether bats are present or not.

At Mid-Essex Hospital Services NHS Trust, we are proud to have high bat activity around our Broomfield Hospital site, with a bat roost of Soprano Pipistrelles known and monitored for several years.  Both Soprano & Common Pipistrelles have been found foraging within our natural areas, feeding on insects during their summer months and highlighting our effective natural management on site. 

Bat walks offer a unique educational opportunity to experience these intriguing creatures, and in 2016 we launched an inaugural Twilight Bat Walk Programme, led by a local bat enthusiast.  The walks proved to be a huge success, providing education in an endangered species whilst promoting healthy walking alternatives within Broomfield Hospital and community.  Following on from these walks, a larger Twilight Programme was produced for the summer of 2017.  

A stunning 400% increase in participation occurred, with over 100 individuals expressing interest, comprising of staff, patients and members of our local community.  David Jackson, the bat enthusiast, and now the Trust’s Sustainability Project Coordinator said ‘It’s been great to see the walk participation increase so quickly…educating those in our community about endangered species is hugely valuable to their future conservation, whilst achieving it through the promotions of an active lifestyle.’ 

Supported by the Essex Bat Group and Heart & Sole Walking Scheme the 2018 Twilight Programme is now available.  Join us with friends and family to experience the hospital site bat activity and roost.  What will you find? 

The Bat Walk Dates 

25th May, starts 8:30pm 

13th July, starts 8:45pm 

27th July, starts 8:25pm 

17th August, starts 7:45pm 

7th September, starts 7:00pm

Spaces are limited, on a first come first serve basis.  If you’d like to express an interest please contact David Jackson on sustainable.development@meht.nhs.uk or 01245 514558.  

Bats in Greywell tunnel, Hampshire

by Paul Hope

Greywell tunnel is a disused canal tunnel on the Basingstoke Canal in north Hampshire. The 1,124m long brick lined tunnel was constructed in tandem with the canal between 1788 and 1794. The tunnel is approximately 5m high and has a maximum width of 4.5m. It was excavated through an area of changing geology from Hampshire chalk through Reading beds into London clay. There was a partial collapse in the tunnel during the 1930s and a further fall during the 1950s that left the bore of the tunnel blocked about 800m from its eastern entrance and at 130 m from its western entrance. Bat friendly grilles prevent public access to the site.

Greywell tunnel has long been known as an important site for hibernating and swarming bats. It was designated a SSSI for bats in 1985. Hibernation surveys are conducted from a boat by a team of up to five surveyors. As you work your way into the tunnel light from the portal becomes a distant dot. During hibernation counts many of the bats encountered are hanging against the brick lining, however a high proportion are often packed into crevices and openings in the brickwork left during the tunnels construction. Within crevices it’s sometimes a matter of counting ears and feet to get as accurate a count as possible and on occasion it’s not possible to record bats to species.

Natterer's bats at Greywell. (c) Roy Champion

Natterer’s bat is the most commonly encountered species (highest count of 569 in 2013), Daubenton’s bat is also regularly recorded (highest count of 69 in 1986). We also often record whiskered, Brandt’s and brown long-eared bats. The count this January gave some very exciting results. We had our second highest count for Natterer’s bat in the eastern end (564) and our first ever record of a greater horseshoe bat. The horseshoe bat is an excellent record for North Hampshire. Bat Group records show it is the seventh on record; this includes two records for Winchester from the 1940s.

Greater horseshoe bat at Greywell. (c) Roy Champion

Sadly after over 30 years of monitoring at the site, future regular monitoring is threatened by a recent move by the owners Hampshire County Council to declare it a Confined Space. Now surveys can only be conducted once every two years due to the excessive costs of gas monitoring equipment and a rescue team stationed outside the tunnel. We do not feel that this is often enough to provide adequate data resolution for the SSSI condition assessment, but Natural England have said that it will be sufficient.

Using acoustics to assess biodiversity in cities

by Alison Fairbrass

Cities now support over half of the world’s human population. They also support endemic and threatened wildlife. This wildlife provides multiple ecological services to human urban populations, and also provides the daily contact with nature that most of us now experience. However, our understanding of how wildlife persists in urban environments, and how we can design and manage cities to provide the best possible habitat for wildlife is still not very well understood. One reason for this is due to the difficulties of assessing biodiversity, especially in cities. Human surveyors have to consider safety issues, survey equipment is vulnerable to vandalism, theft and destruction, and getting access to private land to conduct surveys can be very bureaucratic. Through my Engineering Doctoral research (EngD) I developed new acoustic tools that can be used to make it easier to assess biodiversity in urban environments. These tools should hopefully be used in the future to better understand the biodiversity supported by cities and to inform the design and management of cities for biodiversity.

Acoustics and biodiversity assessment

Lots of wildlife produce sounds, either by vocalising – think a singing songbird - or through movements of their bodies – think the hum from the rapid wingbeats of a bumblebee. Some species also make sounds that cannot be heard by humans, such as the ultrasonic echolocations of bats.

Ornithologists have used the species-specific calls emitted by birds to identify calling species for centuries. More recently, ultrasonic recorders have been used to record the species-specific echolocation calls of bats which can be used to identify species.

But these examples are very species-specific. There are other species that live in cities such as insects and non-flying land animals like foxes and squirrels that also make sound.

The field of ecoacoustics uses the sounds emitted by all species to get a measure of whole ecological communities, rather than focussing on specific species and species groups. Ecoacoustic theory posits that the soundscape (sounds at a landscape scale) of an environment is composed of biophony (sounds emitted by non-human organisms), anthrophony (sounds associated with human activities) and geophony (abiotic sounds such as wind and rain).

The three elements that compose a soundscape: biophony, anthrophony and geophony. Image credit: Pijanowski et al. (2011) BioScience.

New technology for ecoacoustics

The use of ecoacoustics to monitor biodiversity has really been made possible by the development of passive acoustic recording technology, such as the very popular products from Wildlife Acoustics. These are weather-proof acoustic recorders that can be left outside for long periods of time, recording sound on a user-defined schedule. This technology is making it possible for biodiversity scientists and conservationists to collect vast amounts of acoustic recordings.

An SM2+ SongMeter is an example of a passive acoustic recorder that is commonly used in ecoacoustic research. These devices can be deployed in the environment recording at a pre-defined schedule for days/weeks/months at a time. Image credit: www.wildlifeacoustics.com.

But what to do with all this acoustic data? It is not practical or efficient to spend days/weeks/years listening to the recordings that have been made.

To overcome this Big Data problem, ecoacousticians have developed algorithms that can measure the biotic sound in acoustic recordings producing a proxy measure of biodiversity. These algorithms are called acoustic indices and can be used to quickly produce measures of the biotic sound in large volumes of acoustic data. They measure a few characteristics of the acoustic data, such as the amount of sound at particular frequencies, to produce a summary measure of biotic sound within an entire sound recording.

Acoustic indices produce measures of the biotic sound in audio recordings. Four commonly used acoustic indices include: A) Acoustic Complexity Index (ACI, Pieretti et al. 2011 Ecol. Indic.), B) Acoustic Diversity Index (ADI, Villanueva-Rivera et al. 2011 Landscape Ecol.), C) Bioacoustic Index (BI, Boelman et al. 2007 Ecol. Appl.) and D) Normalised Difference Soundscape Index (NDSI, Kasten et al. 2012 Ecol. Inform.). The ACI sums the absolute difference in signal power within frequency bins over time using a sliding window and defined temporal steps (indicated by arrow). The ADI is calculated as the Shannon’s diversity index for each recording based on the signal power occupancy of each 1 kHz frequency band. The BI calculates the signal power within 2-8 kHz frequency band of recordings. The NDSI calculates the ratio of signal power in the frequency bands between 1-2 kHz and 2-8 kHz to measure the level of anthropogenic disturbance on the landscape.

Ecoacoustics in the city

However, ecoacoustic research and the development of acoustic indices has tended to focus on less disturbed environments than cities, such as temperate woodlands, coastal forests and Mediterranean scrub. The challenge of my EngD research was to see if ecoacoustic could be applied in this new, highly anthropogenically disturbed environment.

I started off by assessing the suitability of a suite of commonly used acoustic indices for use in the urban environment. I collected low (0-12kHz) and high (12-96kHz) frequency audio recordings from 15 churchyard sites across the Greater London area. I was lucky to collaborate with the Diocese of London on this data collection while they conducted a London-wide ecological survey of their churchyards.

Setting up my acoustic sensors

To test exactly what sounds the acoustic indices measured in the acoustic data, I listened to and manually labelled the sounds in a random selection of my recordings. To do this, I co-developed AudioTagger, a bespoke audio analysis software that allows you to quickly listen to and view audio recordings, and draw labelled bounding boxes around sounds on spectrograms (a visual representation of an audio recording).

AudioTagger in action. Sound recordings can be quickly listened to, viewed as spectrograms and annotated by drawing labelled bounding boxes around sounds of interest. Sounds labelled here include birds (blue boxes), electrical buzzes (pink) and road traffic (red).

I identified a very wide range of sounds in my recordings. Anthropogenic sounds dominated the dataset and the variety was much greater than in previous ecoacoustic studies, including sounds such as road traffic, sirens, church bells, footsteps, and applause. Biotic sounds were mainly made by birds and bats, and geophonic sounds were either wind or rain.

Of the four acoustic indices I tested, either the measures of the acoustic indices did not correlate with the amount of biotic sound in recordings, or were biased by non-biotic sounds in recordings (Fairbrass et al.2017).
 
Therefore, I would not recommend that any of the acoustic indices I tested are used to assess biodiversity in urban environments.

Machine learning as an alternative to acoustic indices

Machine learning algorithms learn to recognise patterns in data based on examples that they’ve seen previously, for example how a spam email application learns to filter emails based on what a user has previously marked as spam (skip to 32:38 for a great introduction to machine learning).

Deep learning algorithms (a type of machine learning) choose by themselves what characteristics define different groups of data, rather than relying on humans to choose. Therefore they can use many more parameters within data to characterise groups than a human ever could, making them extremely powerful.

Machine learning algorithms are potentially much more powerful than acoustic indices, as they do not rely on human defined characteristics of data. What they do rely on is having a large dataset of labelled data with which to learn the characteristics of different groups.

To train a deep learning algorithm that could measure biotic sound in audio recordings from the urban environment without being biased by the non-biotic sounds in the city, I collected audio recordings from 63 sites across the Greater London area.

I used AudioTagger to label all the biotic, anthropogenic and geophonic sounds in a random selection of 45 minutes of recordings from each of the 63 sites. This labelled data was used to train and test a pair of Convolutional Neural Network algorithms, CityNet (Fairbrass Firman et al. in review), which produce a measure of biotic and anthropogenic acoustic activity in noisy acoustic recordings from the urban environment.

Audio data recorded at 63 green infrastructure sites in and around Greater London (A) was used to train (black dots) and test (red dots) the CityNet system. CityNet can be used to summarise the biotic and anthropogenic sounds in large volumes of audio data from noisy urban environments. A week of audio recordings are summarised here to produce daily average patterns of biotic and anthropogenic sound (B and C), which can be interesting to compare between different types of environments, such as sites in the centre (B) and on the outskirts (C) of the city. Image Credit: M. Firman

The algorithms can be used to produce summaries of the biotic and anthropogenic sound in large volumes of audio data from cities – at http://londonsounds.org/ you can explore the patterns of biotic and anthropogenic sound at my 63 study sites.

Biotic sound as a proxy measure for biodiversity

An open question that remains in ecoacoustics is whether biotic sound is a good proxy measure for biodiversity? And does more biotic sound mean more or better biodiversity? Some have argued that due to the way species avoid calling at the same time and frequency, more sound does correlate with more diversity, but that this relationship only holds in the tropics (Krause & Farina 2016).

To investigate whether biotic sound can be used as a proxy measure of habitats in cities, I conducted habitat surveys at all my study sites and compared local and landscape habitat measures with the biotic and anthropogenic acoustic activity and diversity.

Initial results suggest that there is a relationship between the biotic sound recorded at a site, and the characteristics of the local and landscape habitat. However, this research needs a bit more work before I’m confident in the results, and I will continue to work on this to try and answer the question of whether biotic sound can be used as a proxy measure of habitats in cities.

Next steps

In this research I have found that existing ecoacoustic tools in the form of acoustic indices are not suitable for use in cities as they either do not measure biotic sound or are biased by non-biotic sounds in recordings (Fairbrasset al. 2017). To overcome the shortcomings of acoustic indices, I have developed deep learning tools, CityNet (Fairbrass Firman et al. in review), which measure the biotic and anthropogenic sound in acoustic recordings made in noisy urban environments. Finally, I have found that biotic sound may be a good proxy for the characteristics of habitats in cities.

Cities are exciting places in which to develop new technologies for assessing biodiversity because the availability of power and Wifi connectivity makes it possible to develop autonomous systems for monitoring wildlife. For example, smart sensors and machine learning algorithms have been used to develop the world’s first end-to-end system for monitoring bat populations in the urban environment (www.naturesmartcities.com ). I think it is important that machine learning and sensing technologies continue to be used to improve our understanding of wildlife in cities, enabling us to design and manage better cities for the future.

Daubenton's on ice!

From BCT's Scottish Officer, Liz Ferrell, comes a fascinating story of winter bat behaviour:

Graham White, a nature enthusiast, had never seen a Daubenton’s bat before and certainly not during daylight hours! He therefore felt very lucky to see one (on two separate occasions) over the festive period where he lives in Coldstream, the Scottish Borders. Graham told us he had been walking along a section of the River Tweed on the 4^th December. It was south facing and the bank was getting a lot of warmth - even on a very cold day. The old mill weir also meant the river was slow flowing and about a metre deep. The result was like a mirror with not even a ripple on the water. The only movement came from insects which dotted the surface. And then there it was, a Daubenton’s bat flying over the water at one o’clock in the afternoon!
 
By pure chance, on the 7^th January, Graham saw another Daubenton’s. This time 1.5 miles from the River Tweed flying over Hirsel Lake along with the geese, swans and goldeneye he had been watching. The bat flew right next to Graham and for a further two minutes he watched and photographed the bat before it disappeared into the waterside trees. Graham mentions that the most astonishing thing this time around was that the lake was 95% covered in thin ice! The bat of course had found the other 5% unfrozen water (all thanks to some very clumsy geese after they had landed on the lake).
 
It led Graham to ask what exactly the bats were doing – were they drinking, actively foraging, both, or neither! In truth, it is hard to say. It was certainly a very surprising encounter with this little hunter. I think this story just goes to show that we have so much to learn about bats' activities through the winter and perhaps climate change is also going to have its effects. We all hope that these two bats were able to survive the winter.
 
Thank you Graham White for sharing your story and photos!

Have any readers seen anything similar? I'd love to hear about it!

Mysteries of the night

Mysteries of the night by Helen Hayes MP (species champion for the common pipistrelle)

Everyone finds different ways of coping with the shorter days and colder winter weather but some British wildlife have come up with enviable methods of getting through the worst of this season. As species champion for the common pipistrelle bat I have been discovering more about how this tiny creature, which weighs less than a pound coin, copes with the harshest of winters. Their tactic is to sleep, or rather hibernate, through the worst of the weather and start afresh when the warm weather returns. I am sure many people would quite like to spend winter that way!

Helen Hayes MP at the start of her bat walk

A lot of my knowledge about this tiny flying mammal comes from a bat walk I took part in last October. The bat walk was in West Norwood Cemetery where I was lucky enough to be accompanied by Jo Ferguson who is the Built Environment Officer for the Bat Conservation Trust (BCT) and Ian Boulton, who is the Environmental Compliance Officer for the London Borough of Lambeth. Both of these ecologists provided me with an array of interesting facts about these fascinating and important animals.  All 18 UK resident bat species eat insects and in winter these are just too scarce to be a reliable source of food so all of our bats spend the winter hibernating. Once the weather warms up enough they awake to restart their nightly chase of flying insects again.

The common pipistrelle, a species I am very proud to champion, is found right across the UK including in my London constituency of Dulwich and West Norwood. It is by far the most common bat species in the UK although its numbers are thought to have declined dramatically throughout the 20^th century. I am happy to report that the work of the National Bat Monitoring Programme run by BCT shows that there are some promising signs of recovery in the common pipistrelle bat and some of the other 10 bat species they are able to monitor. Bats are a great indicator of the quality of our environment, so these signs of improvement should be welcomed by all of us.

Despite being the most common bat species, it remains a mystery as to where most common pipistrelle bats hibernate. This mystery is not restricted to the UK and researchers in the Netherlands were surprised to find that large numbers of pipistrelles were hibernating in the expansion gaps in the balconies of tower blocks.  Could some of Londons pipistrelles be hibernating in tall modern buildings? I am sure with the ongoing dedication of all the passionate volunteers involved in bat conservation we may eventually find out their secret but for now much about their lives remains a mystery.

On my bat walk I learned that there are steps we can all take to make cities more welcoming for bats and other wildlife. There is growing evidence that taking this approach is not just good for them but good for us too. Do take a look at the BCT website (www.bats.org.uk) to find out more about bats and how to get involved in their conservation. There are local bat groups right across the UK including the London Bat Group.

This year I will not only be looking forward to the warmer spring weather but will also be keeping an eye on the night skies so I can spot a different sign of spring, the acrobatic flights of the common pipistrelle bat.

Helen Hayes MP receiving her common pipistrelle poster from Kit Stoner (Joint CEO)

To find out more about the Species Champion Project go to: https://www.buglife.org.uk/specieschampions/champions