The Bat Conservation Trust (BCT) run a national bat conference annually – this year’s event was over the last weekend up at the University of York. The event is based around a series of talks, workshops on particular topics and stands run by various manufacturers of bat-related merchandise from books to detectors to jewellery. But the whole thing really hangs (pun out of the way nice and early) on the conference dinner and ceilidg on the Saturday night!

The conference crowd covers the full spectrum from enthusiasts to professionals although in my experience, most people fit somewhere towards the centre with a bias one way or another – the industry of protected species surveys means that the impressive knowledge and experience of bat group members is in high demand even if only on a casual basis. The age range of the attendees is also similarly diverse, from younger graduates to older veterans and again, this is an excellent opportunity for everybody to learn something new.

The opening talk was from BCT chief executive, Julia Hanmer. This provided an overview of the work that the trust has been carrying out over the last year, the initiatives started and the priorities identified. The bad press for protected species in general this year, courtesy of George Osborne, was of clear concern. His rhetoric on the issue was fairly ill-founded, as a government review (the Habitats Directive Review) subsequently found, but the headlines do not help the cause. Other areas progressed include the new guidance issued earlier this year – a revision of the Bat Surveys: Good Practise Guidelines – and the shift in the BCT’s training programme to meet this, alongside an emphasis on greater knowledge-sharing via the mitigation case studies website.

This should certainly be a priority – there is so much work carried out on bats and bat roosts within the UK which is simply not shared outside of the company which carries it out. There must be a vast wealth of knowledge which is untapped and patterns of success or failure which are not being identified. This is understandable within consultancy, with issues of data ownership and client confidentiality always causing concern. One of the most valuable opportunities which the conference offers is to share this knowledge informally with other delegates and gain new ideas or insights which might help to improve mitigation and survey effort. I wonder whether Natural England might be able to assist in this area however; consultants are unlikely to post a case study of how they got something wrong but this can be as (if not more) useful that knowing how they got it right. Natural England on the other hand receive all mitigation proposals which go to licence, and should receive monitoring data on the success of these schemes. If they were able to analyse this vast wealth of information – it would make a fascinating PhD topic if they didn’t have the resources themselves – a huge amount could be learnt and this could provide a much stronger evidence base for consultants to design mitigation.

Linking in very nicely with this topic was a talk by John Altringham on the effect of road disturbance on bat activity and diversity and the effectiveness of current mitigation practice. This touches on both the ‘bad headlines’ often attributed to bats and the issues with mitigation schemes. Bats ‘commute’ along linear features such as woodland edges, hedgerows and rivers to travel between roosting habitat and foraging habitat. These linear features can very easily be severed if a new road is built or an existing road widened to include more carriageways. Species differ in their behaviour in this case – Emma Stone (whose talk appeared later in the schedule) found that even lighting a 10m section of hedgerow would prevent lesser horseshoe bats from using one of their regular routes so imagine how much greater a severance a fully lit tarmacked duel carriageway would present. James Hale (whose presented his study on the Sunday) looked at the behaviour of common pipistrelle bats in Birmingham city centre and found that, although they prioritised shorter breaks in their commuting route, or the darker areas of these gaps, they would use commuting routes which were split by busy roads. These two species are probably towards the extreme ends of the behaviours displayed by bats but each represents a significant concern if a new road is built; lesser horseshoe bats will be separated from habitat on the other side of the road whereas pipistrelles may well continue to cross as they always have, with unmeasured levels of mortality caused by subsequent car-strikes.

The standard mitigation has been to either push bats up over the road – using green bridges, bat gantries, bat wires or similar – or to encourage them below the road through underpasses. These methodologies have been used in the past on several schemes but their effectiveness has not been monitored. Where monitoring has taken place, John Altringham identifies a confusion between ‘use’ and ‘effectiveness’ – if a bat were observed to use a bat wire, it was concluded that the bat wire was used and that the mitigation was therefore effective. However one bat is a fraction of the population – if one bat crosses safely and twenty cross unsafely, this is not effective mitigation. The conclusion reached was that bat wires and gantries – those which draw negative headlines due to their cost – are not effective mitigation. Underpasses were found to be more effective, although there was variation in their utilisation – 94% of bats made use of one which was studied by Altringham whereas another only attracted 30%. There were differences in the height of the underpasses, the position in relation to the original commuting route and other variables which might impact upon this success rate but the key problem is that we simply do not know. I understand that a PhD is about to begin looking at this very issue and I very much look forward to hearing the results and conclusions in a future conference – this kind of scientific approach, with appropriate controls and comparisons is exactly the kind of information which is needed if the work carried out to protect bats and safeguard populations is to be effective.

Charlotte Walters gave a talk later about a new tool – iBatsID – which will take a recorded echolocation call and provide a probabilistic identification of the bat species. The tool was developed using a machine learning algorithm – an Artificial Neural Network – which was fed with a vast number of bat calls from a range of species. The ANN then identified characteristics of the acoustic pulses which could be used to distinguish between different species, and can then work out the most likely identity of any particular call it is subsequently presented with. Bats show a wide range in their echolocation calls – this includes variation in call length (how long the pulse lasts for), the frequency of the call, the distribution of frequencies between constant frequency (cf), frequency modulated (fm) and the range of frequencies which each of these covers, the shape of the call and others – a total of 24 characteristics in all. See image below for a couple of example calls from different UK species – you can see how different they are. The paper presenting the tool can be found here.

This talk, and the questions which followed, provided a glimpse of the slight discord between the extreme ends of the spectrum of attendees. One member of a bat group was disappointed by this approach to bat analysis, feeling that it took away from the skills and experience of a bat surveyor and allowed one machine to feed information to another machine which would then provide the answer that such a surveyor may not be able to interpret. There is validity to this argument if, as he feared, the surveyor would be otherwise untrained or inexperienced but drawing their information from this computerised output alone. However because of the way that larger scale surveys are frequently carried out these days – as a workshop on battling with data by Atmos Ecology staff identified, static detectors could easily record close to a million calls for a single wind turbine study site – the advantages of some level of automated analysis are immense. Tools such as this should, as Walters correctly pointed out, be seen as an useful additional tool for bat workers but are not intended to replace the knowledge and experience which really are critical to good analysis of findings and the ability to propose mitigation and compensation based upon it.

Graeme Smart, from the Northumberland bat group gave a very engaging talk on the Nathusius pipistrelle in Northumberland. This is one of the more rarely encountered species in the UK and there are questions as to whether the Northumberland population are resident or migratory – they are known to be present in every month between May – October but their disappearance in the winter months could be due to hibernation or migration. The migration theory was supported by a sighting of a Nathusius pipistrelle making landfall by a birdwatcher on the beach; the bat was found to be underweight and dehydrated which would support a long flight across the sea. This individual was taken in by the bat group, fed and rehydrated and successfully released shortly afterwards. The bat group are using a range of methods to try to establish whether the population is present over the winter, but the most innovative and exciting is perhaps the attachment of a bat detector to a cross-channel ferry which monitors for bats during the ship’s nocturnal passes. As Smart said, it is a little like looking for a needle in a haystack but that doesn’t mean that it would not be worth looking and it would be fantastic if a bat were picked up via this method. The BCT run a Nathusius pipistrelle survey which aims to extend our knowledge of where this species is found in the country. Nathusius pip’s are very much associated with waterbodies and the majority of roost sites are very close to larger areas of water – if you sign up, BCT will allocate you a lake to visit twice in September to look for this species. I have been undertaking these surveys at a nearby reservoir but with no luck so far!

A later talk by Caroline Moussy from the University of Exeter was tackling a similar question in a different species using very different methods. The serotine bat is largely restricted to the south of England, with a few exceptions which rise up the east and west of the country, but is widespread on the continent. Moussy used genetic techniques to look at what gene flow could tell us about mixing between populations both within the UK (as they fall into three distinct regions) and the European populations. The results found evidence of movement between populations on the continent and the UK residents but very little visa versa. Movement between the Isle of Wight to the western population and the eastern population to the western was also found but very little from the west to the east. Although the techniques used are advanced and require specialist equipment, this approach gives a very definitive answer the questions of movement posed and could, in principle, assist in the question of the Nathusius pipistrelle migration in the previous talk.

One very useful tool for protecting bats is to know where they are and the talk by Richard Dodd on the bats and bikes project showcased a novel way to extend our knowledge of their distribution. This was a partnership between the Nation Cycle Network Sustrans and the local Cardiff and Valley’s bat group. The methodology is fairly straightforward, an AnaBat detector was placed in a backpack with a microphone mounted on the top of the helmet and volunteers cycled 1-hour stretches of the Taff Trail between Merthyr Tydfil and Cardiff and analysed the results upon their return. With a GPS unit attached to the AnaBat, each of these calls was geo-referenced so they could see exactly where each call was picked up. Driven transects have been used for a while now but this seems to be a novel approach to gathering data over a wide area which is not accessible to cars. A total of 401 calls from six species were recorded with some clear habitat associations observed, for example the Nathusius pipistrelle was recorded at points where the route ran alongside a river. I would expect that this methodology could be taken up by more bat groups in the future and I do hope to have a go in an area of local woodland soon as a good way of getting a snapshot of activity throughout the habitat in a relatively short period of time.

Stephanie Murphy presented a talk about patterns of habitat use in brown long-eared bats which tied in rather nicely with the final talk by Toby Thorne on the spatial analysis of roosting associations of BLE’s and Natterer’s bats in broadleaf woodland. Using radio-tracking of 38 brown long-eared bats, Murphy found that primary and secondary foraging areas could be identified within woodlands. Core areas, those which were preferred, frequently had a higher percentage under-storey cover and species richness that the peripheral habitats. There was overlap in the core areas used by different bats which suggests that the distribution of foraging within the woodland may be related simply to habitat quality rather than a more territorial dividing up of resources. Thorne found that, within Finemere Wood, four groupings of brown long-eared bats could be identified, although there was some mixing between groups. This suggests that a given woodland may have a number effective populations and therefore any impacts such as management should not be considered to affect ‘the brown long-eared population’ but perhaps one group more than others. A lower level of non-random association was found between Natterer’s bats which seemed to form less strong associations.

Murphy found that brown long-eared bats switched maternity roosts with some regularity – 21 out of 28 used only one roost whilst others changed up to nine times throughout the season. It would be interesting to see what these figures would show for Natterer’s bats, to see whether perhaps a greater tendency to switch roosts, as found by Smith and Racey in their 2005 paper: The Itinerant Natterer, might influence the pattern observed by Thorne.

Other interesting results presented by Murphy related to the roost sites used by BLE’s; 60% were in buildings whilst 40% were in trees, 27 of the roosts were in oak with one in ash, 63% of trees were greater than 50m from the woodland edge and roost trees tended to be the largest in the quadrat. All of these would be useful characteristics to use when assessing trees for potential roost sites.

I think that the highlight of the conference for me was a workshop on surveying trees for bats, run by Henry Andrews. This talk was fascinating, engaging and eye-opening. Andrews has carried out extensive research, looking outside of the standard sources, and changed the way he approached surveying trees as a result. Brown long-eared bats frequently roost within buildings and received wisdom will tell you that the ridge beam is where they are most often identified. Following this information, Andrews looked at the type of wound/fracture/feature within trees which was most likely to provide similar conditions in trees and came up with the stress fracture – an often horizontal split in a branch which creates an upwardly extending cavity with dry conditions which is very similar to the ridge board of a house. His first targeted inspection of one of these features turned up a roost.

He provided the workshop group with a range of ‘roosts’ – actual logs and pieces of timber cut away to reveal the internal structure so that from a woodpecker hole, the trunk was opened out to show the nest cavity within. Similarly were examples of frost and snow damage, rot holes and the stress fractures, as well as the features which can be made when a tree splits to multiple leaders and a cavity forms at the join. Alongside these examples was information on what evidence to look for, where to look for it, when and how to carry out the surveys and a brief guide to the best kit for the job.

Andrews has gathered together information from many bat workers on the nature, location and features of tree roosts and has produced a guide called the Habitat Key for the Assessment of Potential Bat Roost Features in Trees which can be downloaded from his website. This is an excellent document which really typifies the type of information which needs to be brought together, collating experiences to allow broad trends to be identified as well as the more exceptional situations which show just how dangerous it can be to rule things out. Received wisdom is not always correct! He has promised an update towards the end of the year and I very much look forward to this becoming available.

My own contribution to the knowledge of bats in the UK is as follows: Judging from the relative abundance of different species as ‘incidentals’ within slideshows throughout the conference, it can be concluded that the most appealing/photogenic species is… the brown long-eared by a small landslide!

Here’s looking forward to next year’s conference, details will become available on the BCT webpage sometime next year which should be found here!
If you are interested in getting involved in bat surveys or to find out more about these fascinating creatures, try contacting the local bat group, both the Lincolnshire Bat Group and the Leicestershire and Rutland Bat Group are very friendly, welcoming and knowledgable. They will also be able to help if you have any bat-related queries or if you find a grounded or injured bat. If you want to support the fantastic work of the BCT and help conserve British bats, think about joining them here! Their website also has lots more information about British bats including individual species fact sheets here.