I recently travelled up to Scotland to attend a Bat Handling Course run by Echoes Ecology in Polmont. The course was an opportunity to refresh and practise my bat handling skills as well as gain more experience in the techniques used to capture bats.
The course involved two nights of trapping. On the first night we used a hand net to catch soprano pipistrelle bats at a roost near to Loch Lomond. The small size of this species requires care and delicacy when handling to ensure that their wellbeing.
The second day was spent in the Echoes Offices with presentations on handling technique, bat identification, health and safety considerations and licensing. The atmosphere was relaxed and informal as well as informative, with discussion between candidates and course leaders.
On the second night, we went to a viaduct site to capture Daubenton’s bats leaving a roost in the side of the viaduct wall. We also set up a mist net and captured a soprano pipistrelle foraging beside the canal.
I have put together a short video of the harp trapping at the viaduct, including some trailcam footage of bats exiting the roost and encountering the harp trap. This was using the ‘Field Scan’ setting on the Bushnell Trailcam as bats do not seem to trigger the unit in my experience.
I hope you enjoy the video below – if you would like further information on the courses run by Echoes Ecology, which include ornithological courses as well as bat courses, visit their website or their facebook page for more information.
The Artificial Lighting and Wildlife conference was held in London on the 20th and 21st of March 2014. It’s scope included effects on a range of wildlife but, being sponsored by BCT, bats were a key focus. Full details of the symposium can be found here. This is a short piece I wrote up for the local bat group but I’ve added in the references and a couple of illustrative photographs below!
Artificial lighting is ubiquitous and almost universally accepted – we have street lights for crime prevention and traffic safety; architectural lighting of statues and churches; lighting of industrial sites to allow work to continue 24/7; and light spill from inside houses. Three scary facts which illustrate this are:
Variations on this photograph – a satellite image of the earth at night showing the extent of artificial lighting – were the most widely used photograph throughout various talks and rightly so – it serves to show just what an impact we have on the natural environment. Photo copyright: NASA
Most bat workers will know of research, such as Emma Stone‘s work in Bristol, which shows that slower flying species such as horseshoe, long-eared and myotis bats tend to avoid light and that lighting their commuting routes can cause severance. Much of the interesting new research at the symposium came from Holland; Herman Limpens looked at whether there are more ‘bat friendly’ lighting spectra and found that amber light caused much less avoidance than white or green light on bats commuting along a dark canal corridor. This was also borne out in analysis of Irish monitoring surveys which found much lower levels of Daubenton’s activity at lit waterway locations. Fiona Matthews from Exeter University put paired static detectors in light and dark locations in a 2km radius around greater horseshoe roosts and found much higher activity levels were recorded in the dark.
Bats can be disturbed when roost entrances are lit: the Life at Night project changed the lighting regimes of churches in Slovenia and achieved significant improvements in both emergence time – horseshoe bats left earlier – and consistency – bats left over a much shorter time period. Kamiel Spoelstra from the Netherlands Institute of Ecology found pipistrelle occupancy rates of boxes to be significantly reduced under white and red light treatments compared with dark.
The ubiquitous Illuminated Church – the subject of the Life at Night talk (photograph from the Life at Night Project Website http://www.lifeatnight.si/en/)
But the picture is not that simple; some species such as pipistrelles and Leisler’s are actually attracted to streetlight. Their speed makes them less susceptible to predators and anybody who has undertaken moth trapping will know that moths gather at light sources, especially attracted to shorter wavelength and UV light. A fascinating talk by Andrew Wakefield from the University of Bristol added a further dimension to this – he found that the avoidance behaviour usually exhibited by moths in response to a bat echolocation call – a change of course or a power-dive where they drop to the ground – is reduced by 60% under lit conditions making them a much easier prey for bats.
The impact of lighting upon invertebrates was widely discussed; for example it was found that larger moths with larger eyes are most attracted to shorter wavelength light and they are drawn in at 6x levels compared with longer wavelength light. This attraction is well known but the implications are rarely considered; Matt Shardlow of Buglife estimated that a third of interactions between moths and light sources would prove fatal to the insects through exhaustion, collision, heat or predation.
The influence which lighting can have upon the relationships between species was a trend which came out in a number of the talks – the impact then can be considered positive or negative, depending upon your perspective. Parasitoid rates on moth eggs were much higher under lit conditions as the diurnal parasitoid gains the advantage. Redshank increase their foraging in lit areas, favouring the redshank (perhaps?). Similarly, a Leisler’s bat can forage more efficiently, but to the detriment of the moths which are preyed upon. Lighting at night disturbs and disrupts the natural rhythms, dynamics and ecological signals.
A peacock butterfly seeking out a dark place to hibernate.
One of the last talks of the symposium was from Kate Harrington who found evidence for in-combination effects of artificial light and artificial noise on bats – as the two are so often associated such as from traffic along well-lit roads, the potential for this to modify the natural environment more severely is significant.
Several talks discussed the importance of good design in lighting schemes for new developments – light only where it is required, light as low as required and design cut-offs and cowls to avoid unwanted light-spill onto surrounding habitats. The project along the Thames at Richmond is an excellent example of this – this video shows how the lights respond to pedestrians so that they feel they are walking in a pool of lights whilst all around remains dark. The importance of maintaining dark corridors was also an important part of the London 2012 park design.
The copper beech outside the Guildhall on the High Street in Grantham showing the extent to which lighting is a normal and accepted component of our villages, towns and cities.
But new designs are only going to reduce future problems – as I walked back from Grantham station after the conference I was shocked to see the level of light-spill onto hedges, trees, the River Witham and other suitable foraging and commuting habitat. I had never appreciated how much of an effect our lighting of the environment would have upon the species we share it with. BCT will be putting up the videos of the talks and presentations in due course so keep an eye out for the news of their arrival!
This week is National Nestbox Week which encourages people to put up nest boxes in their gardens. This is a great idea and focuses attention on providing these features as the birds first start to pair up and scope out nest sites. We have birds nesting in various locations around the garden but, for some reason, I had never got around to adding some more purpose built nesting habitats for them – something I have now rectified!
But why stop at providing habitat for garden birds? Don’t forget that gardens are vital to some of our most common bat species, such as the common pipistrelle and the brown long-eared. Attract bats to your garden and you will be able to watch fantastic aerial displays as the sun goes down throughout the summer. There are lots of tips from the BCT on how to attract bats to your garden.
There are many designs of bat box on the market and plenty of designs which you can make for yourself. I realised that the offcuts of wood we had in the shed provided everything I needed to make a Kent Bat Box – one of the simplest designs and one I would strongly recommend to anybody putting one together for the first time. This box is very simple and creates cavities which small bats such as common pipistrelle can use as a roost. This video shows the kind of tight niches which are used by pipistrelle bats.
Bats fly in the garden regularly throughout the summer and one of them – probably a brown long-eared – uses the porch as a feeding perch. I know this from the little piles of moth wings which suddenly appear some mornings, often 5-10 of them. The bats bite off the wings of the moths they have captured, eating only the nutritious bodies of the moths and leaving the wings to flutter down. Just opposite the porch is a holly tree and this struck me as the ideal place to put a box, seeing as I know the bats use this little niche of the house and garden.
Moth wings in the porch – they have caught on the spider’s web on their way down but there are tell-tale signs that a bat is responsible – especially as so many appear overnight in a single night!
I also put up another box on the tree beside it, facing the opposite direction. We were recently called out to climb a tree to check a bat box where the tree was to be removed. The bat box had only been up for a few months and was clearly un-used so we were able to inspect it and take it down without causing disturbance to any bats. There was nowhere else on the site to place the box so I have put it up in the garden instead – I am interested to see if either of the boxes are used and whether a particular design might be preferred.
If you are putting up a bat box, make sure it is high above the ground (at least 4m if possible) to deter predators and ensure that there is not too much disturbance to the bats as you use the garden. Another important point is to ensure that there is a good fly-in and fly-out route for the bats. This can be achieved by imagining the bats dropping from the entrance in an arc which is 1-2m out and 2-3m down. If you have left this space for them, they should be able to enter and exit the box. Another important point is to allow them to emerge into some cover, if possible, or out along a hedge or tree line. Bats use these vegetative features for commuting around the landscape and placing your box in such a location should increase the chances of a bat moving in.
The designs for the Kent Bat Box can be found here and all you need is a plank of wood, some smaller wood for battons, a saw and a drill (or hammer and nails). The design is very simple to follow but below shows the step-by-step progress of the construction.
The log shed with offcuts we’ve been given for the log burner – but there is a Bat Box there just waiting to be built!The constituant parts of the Kent Bat Box, cut to size. At the bottom you can see the three boards of varying lengths, at the top right is the top for the box, top left are the battons used to create the cavities.This shows how the main pieces fit together – the battons are attached to the long-sides of the boards which are going to be placed one on top of the other onto the longest back-board.The pieces constructed in the last image are placed, one on top of the other, with the smallest at the top and the largest (the backboard) at the bottom to create the two cavities which will form the roosting sites for the bats. These are drilled securely together.Attach the top. As with all bat boxes, the crevices will be downwards facing as bats will land and climb up int the crevices to roost. The top will keep the cavities dry.A view from the base of the Kent Bat Box showing the crevices which will for the roosting opportunities for the bats.The chosen location for the bat box – after a bit of ‘gardening’ to clear leaves and twigs away from the fly-in to the box.The new bat box securely attached using a bungee cord to ensure that the fixing does not damage the tree as it grows. The box is about 4m off the ground with a clear fly-in below, opening onto further shrubs and cover for the bats.
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.
Serotine bat in the hand
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.
A few examples to illustrate how bat calls can vary – each distinct call is a single echolocation pulse. The noctule has long, low, CF calls, the myotis has straight, mid-range frequence FM calls and the pipistrelle has an FM sweep with a CF tail. I have put these calls together manually (they weren’t all flying together) but the platform for the analysis is the BatSound application. Each call is a single echolocation pulse, bats emit a series of these at a frequency anywhere from around 5 per second for a slower noctule pass and 20 per second for a faster myotis pass.
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.
Hibernating brown long-eared bat in a bat box
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.
Grantham Ecology 