The Cumbria Bat Group kindly let me come along on a hibernation survey at Easegill Caves in January 2017. We hiked up to Upper and Lower Kirk Caves to see what we could find, then descended using ropes and caving ladders into Link Pot to explore an underground cave network some 15m down.
We found good numbers of myotis species including Daubenton’s, Natterer’s and whiskered/Brandt’s/Alcathoe – these last three are grouped as it’s very difficult to distinguish these three without disturbing the bats. We also found a small number of brown long-eared bats hibernating too.
It’s important to note that disturbing hibernating bats is illegal without a licence from Natural England – this survey was led and supervised by licenced bat workers who ensured that disturbance was kept to a minimum whilst allowing the bats to be identified and counted. If you find a bat in roosting you should take great care not to disturb it especially during the winter as they may rouse from torpor at an inappropriate time and be unable to then survive the winter. If you do find a roosting bat – let your local Bat Group know! More details at the bottom…
The video below shows a summary of the seven hours we spent out in the hills, in just under three minutes!
The following photographs show a few of the hibernating bats we identified on the surveys.
It’s not only bats we found in the caves – plenty of cave spiders and hibernating moths too including herald and tissue moths.
If you would like to get more involved with your local bat group and help out on hibernation surveys such as these, you can find your nearest here. Many thanks to the South Cumbria Bat Group, and Rich Flight in particular, for a great opportunity to explore the caves and see plenty of roosting bats!
The first talk was from Helen Miller – BCT’s Woodland Officer. A wide range of bats utilise woodland habitats for activities including roosting, foraging and commuting. National Biodiversity Network (NBN) data shows that there is a positive association between bats and the extent and proximity of broadleaf woodland whilst other analysis show that roosts of 5-6 of our bat species are significantly closer to woodland than would be expected by chance. The peripheries of woodlands are frequently used by edge specialists such as pipistrelle species, noctule and Daubenton’s bats, whilst the interior is favoured by other specialists such as the brown long-eared, Natterer’s and Bechstein’s bats. The importance of woodlands to bats are reflected by the number of documents which are available to offer guidance on the management of woodlands for the benefit of bats including the Woodland Management for Bats, Development of Good Practice Guidelines for Woodland Management for Bats, and the UK Forestry Standard.
A history of British Woodlands (Oliver Rackham)
The next talk was by Oliver Rackham whose books on the history of the British countryside – especially woodlands and wood pasture – represent the authoritative texts on the subject. The fabled ‘wildwood’ land cover of the UK historically is likely to have been a complex and dynamic grassland/woodland mosaic which cycled on a roughly 1000 year basis. Factors such as drainage, fertility and the actions of herbivors would have prevented the comprehensive woodland cover which most people imagine. This habitat is still found in wood pasture and parkland habitats where the trees and grassland co-exist and these habitats are where the ancient, gnarled trees are most often found. Closed woodland is not conducive to the development of ancient trees as they are out-competed over time whereas they can survive as standards in parkland, and the grassland/woodland mosaic of the wildwood is likely to have naturally created these trees. The management of ancient woodlands has, for hundreds of years, been for the benefit of the locals and foresters. This meant that trees were coppiced and pollarded to allow them to be sustainably harvested – the development of large trees would be outside of the ability of the foresters to deal with, before the advent of power tools. Oliver Rackham suggested that this may mean that woodlands of the past may have been less useful to bats as these larger ancient trees were not present.
Henry Andrews, who has done much work recording and collating records of tree roosts, pointed out that this assumption that bats are associated with ancient trees is often false as roosts frequently occur in many much younger and smaller trees which are more likely to have been a component of these managed ancient woodlands. Henry Andrews’ Bat Tree Habitat Key page on facebook has many videos of the much younger trees which develop roosting features. Oliver Rackham suggested nonetheless that perhaps ‘bats have never had it so good’ in terms of roost availability with extensive roosting opportunities associated with more larger trees in less managed woodlands. There do, from personal experience, seem to be many features apparently suitable for roosting bats in woodlands where I have climbed and inspected. This would suggest that it is perhaps the loss of foraging habitat, the mechanisation and intensification of agriculture and the impact of these on the insect food source of bats which is responsible for their huge decline across the 20th century.
Branching out: understanding the importance of woodland to the barbastelle (Matt Zeale, University of Bristol)
Ian Davidson-Watts gave two talks back-to-back, first covering Matt Zeale’s talk on the importance of woodland to barbastelle bats before moving on to his own topic. Barbastelles are a rare species in the UK – sparsely but widely distributed. They are mainly tree roosting and specialise in foraging on hearing moths – that is those which are able to hear bat echolocation and take evasive action. This ability has developed in an evolutionary arms race with the result that barbastelle echolocation is 10-100x quieter than similar species. They are a stealth predator and they may therefore be under-recorded by acoustic survey methodologies. The barbastelle bats radiotracked in the study spent the first 1-2h in their roost woodland but would often forage 6-7km from their roost throughout the night with some individuals travelling 12-17km. Many of the barbastelles studied are highly associated with foraging habitats over water, although studies in 2014 on a Lincolnshire colony found that these individuals did not appear to exhibit this habitat selection. The bats roosted most frequently under loose bark with 80% of their roosts being found in these features although splits were also used. The nature of these roosts is transient as they are often in dead or dying trees – only 22 of the 36 roosts found during one year were still standing and suitable the following year indicating a high turnover of roosts. For this reason it was argued that the woodland, rather than the individual trees, should be considered as the roost.
Life on the edge – the importance of woodland to pipistrelles and other ariel hawking bats (Ian Davidson-Watts)
Pipistrelle bats are often thought of as ‘edge’ or ‘generalist’ species reflecting their use of this semi-cluttered environment such as woodland edges, gardens and hedgerows as opposed to a dense woodland or open grassland. Ian argued that this is too simplistic – 43% of bats captured in woodland interior in trapping surveys were common or soprano pipistrelles and a bat logger found that 50% of calls within the woodland belonged to these two species showing that they do forage within the interior of woodland and are one of the most common species encountered there. Pipistrelles are often seen foraging around the canopy of woodlands even before sunset and Ian suggests that up at this level, there is a lot of ‘edge’ between tree canopies and the air, if we consider the woodland in a 3D manner rather than from our own perspective on the ground. Common pipistrelles showed a selection for deciduous woodland whilst soprano pipistrelles show a significant selection for riparian woodland habitat.
Brown long-eared bat woodland ecology (Stephanie Murphy)
This study radiotracked 38 brown long-eared bats in 18 different woodland sites and monitored their movements over 3-6 days. The researchers identified a core foraging area for each individual which was an average of 2ha along with further peripheral foraging habitat where the chance of encountering the bat was around 50%. There was an increase in range size as the active season advanced as well as an increased use of hedgerows for foraging in July and August (although the latter did not account for the former). The key difference between the core and peripheral foraging area seemed to be a more diverse understorey – hawthorn, alder and hazel were more prevalent in the core areas. Bats which were caught together were often found to overlap their foraging areas but did not interact. They were however more likely to be found roosting together.
All female bats monitored roosted in, or adjacent to, the woodlands in which they were captured. 46 roosts were identified – 14 of these were in buildings whilst the remainder were in trees. All of the tree roosts were in oaks with the exception of one ash. The trees tended to be amongst the largest trees within the 50 x 50m quadrant they are in, and 21% of the roosting features used were not visible from the ground. The majority of tree roosts were more than 50m from the woodland edge. Around 50% of the bats used only a single roost during the trapping period whilst 25% switched once and the remaining 25% switched 2-7 times. Colony sizes were larger in building roosts than in trees and switching of roosts was more likely in trees than in buildings.
16 years of ringing Bechstein’s bats – what it has told us (Colin Morris)
The Bechstein’s bat is one of the rarest in the UK – it is a large myotis species with distinctive large ears which is a woodland specialist. Ten bats were radiotracked over two summers and were found to use foraging habitat ranges of 7-50ha at a maximum distance of 300-900m from their roost. There was a strong preference for closed canopy with understory – water and pasture foraging areas were the second and third most favoured habitats.
The Bechstein’s bats in the Brackett’s Coppice in Dorset make use of Schwegler bat boxes erected by the Vincent Wildlife Trust. Both the large 1FW and the smaller 2FN boxes are used by the bats – the large 1FW boxes are used as maternity roosts with a strong preference shown for these in June and a strong preference for the smaller 2FN boxes in May and September before and after the maternity season during the ‘transitional periods’. The bats using the boxes are monitored and ringed and this has allowed their population dynamics to be observed over a long time frame. The number of babies varies significantly, between 10 and 50 over the 16 year study period. There is significant inter-year variation in the sex ratio of the young but this balances out to almost precisely 50/50 over the time frame. Rainfall is identified as the most significant factor affecting juvenile mortality. One of the first bats ringed in 2000 has subsequently been re-captured 47 times, had 10 babies and is at least 14 years old. 25% of Bechstein’s bats bred in their first year; 38% in their second; 28% in their third; 7% in their forth; and 2% in their fifth.
This talk highlighted the value of ringing studies – there is no other technique which would allow this data on longevity, breeding success and population dynamics to be gathered.
A standardised method for survey and monitoring of woodland bats (John Altringham)
John Altringham has developed a protocol for surveying woodland bat species. The hope is that this methodology, which uses Petterson detectors and a piece of software developed by the team, can be used by volunteers up and down the country to identify the occupancy of woodland bats including rarer species such as Bechstein’s and barbastelle. Sixty woodlands would need to be surveyed three times throughout the year to allow the populations of these species to be monitored. It is hoped that the scheme could be rolled out as part of the BCT’s National Bat Monitoring Programme (NBMP) in the future.
Advanced survey techniques for woodland bat species (Daniel Whitby)
Acoustic lures were first developed by Frank Greenaway in 2001. These are effectively speaker systems which emit high frequency calls – either recordings of bats social calls, or a digitally recreated version of these. There are now a variety available for researchers to use to increase the capture rate when trapping bats to identify, tag or ring. There is some discussion on how these lures work – studies of brown long-eared bat suggest that the lures may work be eliciting a territorial response as the capture rate was much higher in the core foraging area than the peripheral foraging area or outside of a bat’s foraging area. There are many positives to using lures. They increase the trapping rate allowing more information to be gathered in a shorter period of time and therefore causing less disturbance to local bat populations. This also makes trapping cheaper in terms of surveyor man hours. There is an increased accuracy of recording species and identifying the species assemblage present, as well as the ability to capture specific species as in the Bechstein Bat Project in the south-east. The lures also help to capture foraging bats as well as the commuting bats which are more frequently captured by mist nets and harp traps. Negatives are also to be taken into account – there is much variation in the way in which different lures work and which calls are played which may make standardisation and comparison between studies more difficult. Some lures may be limited to particular frequencies and so may miss higher frequency components of a sopcial call for example. There is a poor understanding of precisely how the lures work and the use of this technique requires more care, expertise and training than standard trapping techniques.
Reliable tree-roost indicators (Henry Andrews)
Henry Andrews, author and compilor of the Bat Tree Habitat Key ran through his top three indicators that a potential roost feature (PRF) is a roost.
The presence of actual bats came in at #3. This is because the bat may only be present for a night or two and therefore the chances of encounter are not necessarily that high. The best field sign is the longest lasting field sign and therefore, counter-intuatively, the very definite evidence of an actual bat is not number one! Care must be taken when using an endoscope with actual bats involved – a Level 2 licence (as opposed to the basic Level 1) is required to use this equipment. Henry’s number one rule is that you should never touch the bat. Henry offered the guidance that an inspection of a PRF should take 30 seconds – 1 minute and that the bat should remain lit for no more than 10 seconds.
In at #2 is the presence of droppings as these often remain when the bat has left. DNA analysis of droppings can give you a confident identification of the species for a very cheap price – around £45 from Warwick University – and therefore a dropping can be as good as a bat. Look for droppings in spiders webs (which often preserve dropping intact), on leaves, branches or any surface below the roost entrance. Sycamores are particularly good as their leaves are sticky!
The #1 indicator is substrate condition because bats modify a PRF in ways which no other species do. Smooth, bobbled, bumpy, waxy, blackened and polished surfaces inside the PRF indicate the presence of bats. These characters are best described with photographs to aid understanding – there are many example photographs and more information on these features in the Bat Tree Habitat Key – a free download.
The Warwickshire Barbastelle Project (Lois Browne)
Lois Browne gave an inspiring talk on the Warwickshire Barbastelle Project which has been running in Warwickshire for the last two years. This project studied the behaviour and habits of one of the rarest bat species in the UK through trapping and radio-tracking as well as traditional acoustic survey techniques. The study colony roosts in an ancient woodland site but forages further afield, leaving the woods and foraging in a valley to the south as well as around lakes and woodland fragments within 5km of the roost. Non-breeding bats were found to travel further to feed; up to 7km from the roost. Some bats were found to have very traditional routes which they stuck to each evening when they left the wood to reach their foraging grounds. Boxes erected as part of the project were used by the barbastelles, including use by maternity colonies. They found the Colin Morris design to be used preferentially. The project also carried out targeted work to enhance the local habitat for barbastelles, informed by the findings of their study. So far they have planted 800m of hedgerows and standards to improve connectivity, are developing three new wildflower meadows and have built a new pond.
The ecological effects of woodland management (Keith Kirby)
Oliver Rackham’s talk illuminated the way in which all of our woodlands were historically managed and that this human interaction has shaped their structure for centuries. Keith Kirby provided an overview of the ways in which management affects the ecological character of a woodland.
Planting of trees affects species composition which has a significant effect on the associated specialist species, lichens, the abundance of flora below the trees, the nature of leaf litter, deadwood and shade.
Management affects the age structure of the wood through selective felling and other management techniques such as coppicing. It also affects the spatial structure, by which parcels of the woodland are managed, and the vertical structure which affects the species composition which uses them.
Natural deadwood levels on the forest floor are around 100 cubic metres/ha whereas a worked coppice has <10 cubic metres/ha and minimal intervention areas typically have 30-50 cubic metres/ha. This significantly affects the invertebrate and saprophytic communities which are present.
Management of herbivores also affects the woodland structure and character. Since we have effectively wiped out any large predators in the UK, humans are left as the only effective managers of species such as deer which have hugely complex impacts and interactions on a woodland.
Finally, all of these management decisions interact with other factors, such as climate change and nutrient levels, as well as each other. This whistle-stop tour through the ecological impacts of our management reflects the importance of taking the requirements of bats into account when considering how to maintain a woodland.
The principles of ancient woodland restoration (Jeremy Evans)
Planted Ancient Woodland Sites (PAWS) are current plantations – such as coniferous forestry – which occupy the footprints of ancient woodlands which are defined as those which have maintained continuous woodland cover since 1600. The Woodland Trust takes the view that these are ‘damaged but now written off’ and Jeremy Evans talked about the strategy which the Trust takes to restoring these sites. First they identify remnant ancient woodland features which might include ancient woodland flora, old pre-plantation deadwood, archaeological remains or mature oak coppices. The level and immanency of the threat which these features are under is then identified and actions prioritised to take the most at-risk features out of immediate danger. This might include releasing old coppices from out-shading by halo thinning, or selective thinning to bolster the woodland flora. Once these remnant features are secure, Phase 2 is the movement towards a semi-natural composition through thinning, small-scale selective fells and restoration with native trees. The activities are planned, observed and recorded throughout so that the success can be monitored and feed into future restorations.
The Countryside Stewardship Scheme, woodland management and bats (Mike Render and Carol Williams)
The main priority of the Countryside Stewardship Scheme will be to deliver the objectives of Biodiversity 2020 where the success or failures of different species will be the litmus test for success. The scheme will have a ‘two tier’ approach to delivery conservation benefits for species. All UK bat species will be included within the Mosaic Approach which aims to provide broad, habitat scale enhancements which would benefit a wide range of species. Grants will be available within the scheme for woodland creation and management as well as measures to address tree health issues and all of these interventions may serve to benefit bat species falling within the mosaic approach.
Species which are of higher conservation concern would also be catered for through the Bespoke approach – this would involve the development of prescriptions for habitat creation and management specifically designed to benefit these rarer species. The prescriptions will be developed by NE species specialists with input from the BCT whose roost data will be used to identify hotspots for site specific and landscape level interventions. Species falling within this Bespoke approach would include greater horseshoe, lesser horseshoe, grey long-eared and Bechstein’s bats – there are ongoing discussions as to whether barbastelle bats may also qualify for the Bespoke interventions.
Management risk: We must open our eyes and make significant changes to accepted and widely practiced forest management in the UK – diversification of tree species and genetics within species (John Weir)
Two thirds of woodland in the UK is broadleaf woodland and 70% of the canopy cover of these woodlands are made up of just five species. Oak represents 32% of our trees; ash and beech cover 14% each; sycamore is 11% and birch is 6%. Sweet chestnut, alder, hazel and willow are the next four species in line. This dominance of a small number of species means that diseases and pests could lead to dramatic impacts upon our woodlands – Dutch elm showed that an entire species can be all but wiped out by disease. One of the reasons why the English elm was so susceptible was that its ecology and past management meant that many trees in an area were genetically identical and so there was less scope for resistance than would be expected – this issue is relevant today with mass plantations of nursery stock trees, often imported from the continent leading to the globalisation of tree disease. The graphs showing incidences of pests and diseases in recent years is truly terrifying.
Climate change is another issue which is destined to affect all aspects of ecology within the UK over the next few decades and woodland is no exception. John posited the assisted migration of native trees as a way to help woodlands to adapt to this change. This would involve the supplementing of trees of local provenance with trees originating from 2-5 degrees south which will have developed in similar climatic conditions to those which will prevail in the future. They will be better adapted to the warmer climate and the likely increases in droughts which will accompany it.
The susceptibility of our woodlands is something which we need to acknowledge and begin to address to minimise the risk and mitigate the impacts which will have huge knock-on effects to the species which depend upon them, including bats. The powerpoint of John’s talk is available here.
The use of woodlands by bats in anthropogenic landscapes – implications for policy and practice (Kirsty Park)
During the summer, female bats band together in maternity colonies to bring up their young. Previous studies have found that Daubenton’s bats segregate during the maternity season so that female bats access the better quality foraging habitats whilst the males occupy less optimal habitats. One of the studies conducted at Stirling University looked at the sex ratio of bats in urban woodlands – females were found in better quality habitats with mature trees, an open story, a more compact shape and better connections with other woodlands whilst males were found in a much wider range of woodlands. Kirsty’s talk also touched on the use of plantation woodlands by bats – these are generally considered to be less favoured but initial results of an ongoing study found a 30% greater number of echolocation calls recorded in plantation compared with broadleaf woodland sites – primarily soprano pipistrelles including lactating females. This indicates that our view of the relative value of woodland types for bats may need to be re-assessed with increased research.
Wood pasture and woodland bats – restoring the first without losing the second. Lessons from Croft Castle, Herefordshire. (David Bullock)
Oliver Rackham’s talk earlier in the day highlighted the prevalence of ancient trees outside of woodlands and subsequent talks expanded on this to identify the development of woodland around ancient trees as a threat which can lead to their decline and death through competition and shading. At Croft Castle, the National Trust are aiming to fell the coniferous plantation around retained ancient and veteran trees to restore the habitat to a wood pasture habitat with mature trees and grassland which supports many rare lower plant species and invertebrates. This conservation objective would serve a range of species but there would be impacts upon the existing assemblage of bat species – including rare species such as the lesser horseshoe and barbastelle – which favour the woodland habitat which is on site at present. The aim of the National Trust scheme is to retain habitat and linkages for the bat species, through the retention of large western hemlock corridors through the re-created parkland to ensure continuity of woodland habitat. The Trust will track the distribution and abundance of bats in 2015 and beyond in order to monitor and assess the success of this strategy.
Integrating bat conservation into multi-objective woodland management – a case study focussing on Swanton Novers Woods (Ash Murray)
Ash Murray presented a case study on woodland management for bats focussing on Swanton Novers Woods in Norfolk. Different management creates woodlands with varying benefits for bats – active coppicing provides good foraging habitat but poor roosts whilst neglected coppices are the opposite. High forest can provide both good foraging and good roosting habitat but this is not viable as cover across a managed, working woodland. The strategy taken to address this is managing the woodland in varying ways throughout the site including short, medium and long-term coppice, high forest, minimum intervention and Planted Ancient Woodland restoration. The Great Wood is managed on a commercial basis to support the conservation objectives of the wood (designated as a National Nature Reserve) and this multi-objective mosaic approach to management ensures continuity of resource for roosting and foraging bats as well as the vast number of other species which depend upon the woodland.
Social structure of bats in Wytham Woods
This final talk was a deviation from the published programme but was a fascinating way to end the day. Wytham Woods in Oxfordshire is owned by Oxford University and is said to be the most studied woodland in the UK. There are 1273 Schwegler bird boxes within the woodland which are monitored for the nesting bird species. But after the birds have finished nesting and vacate the boxes, the bats move in for the summer– 1051 roosts have been recorded representing 82% of the boxes within the woodland. Those not used tend to be those along edges with boxes in other habitats – ranging from ancient woodland, plantation and rides – being frequently occupied. From extensive surveys, the researchers identified that 13 checks were required to confirm a roost using a saturation curve assessment.
Natterer’s, Daubenton’s and brown long-eared bats are the three key species with a further five species also recorded using the boxes. The three key species have different social structures, as revealed by ringing surveys. The ~600 Natterer’s bats exist in seven different colonies within the woodland and both males and females very rarely mix with other colonies. The ~600 Daubenton’s bats have 5-6 female colonies which rarely mix, although the males move between the different colonies and sometimes form large bachelor roosts of up to 62 bats. The ~400 brown long-eared bats have 21 different colonies through the woodland and they don’t mix at all.
This complex social structure needs to be understood if the impacts of management are to be truly understood – the coppicing of one area of woodland may remove the core foraging habitat for an entire colony and this was found to happen during the monitoring and the colony had to move to a different area of the wood.
It’s very nearly Halloween – what better time to introduce you to the bats which haunt Grantham Canal when darkness falls…
I spent several nights this September cycling along Grantham Canal with an EM3 bat detector connected to a GPS unit, recording the bats in flight between the A1 to the east and Hickling Basin to the west. Bats use echolocation to navigate and hunt and the bat detector converts this ultrasonic sound into something we can hear. The sound emitted by the detector tells you when a bat is there, often which species it is and sometimes even what it is doing.
You might imagine that this is quite a sinister place to be, surrounded by bats on a moonlit night, but there really is nothing to be afraid of! As the detector tapped and pattered away to announce their, I could see bats flying before me in the darkness. But even though I was cycling towards them, they elegantly avoided me every time, never making contact and certainly never tangling in my hair. This is one of the most enduring myths about bats but their fantastic echolocation abilities mean that they can ‘see’ and avoid obstacles on even the darkest of nights.
I recorded at least five species in September, some calls with ‘buzzes’ indicating foraging and some with ‘song flight’ where male soprano pipistrelles emit lower frequency social calls to attract mates. These are just on the edge of human hearing and can be heard without a detector – you may have heard the very high frequency chirrups if you walk outside at dusk in the autumn.
The common pipistrelle is our most abundant species in the UK, and was encountered throughout the route of the canal, particularly where there are more trees as this species specialises in hunting along ‘edge’ habitat which is typically along hedges, tree lines and other landscape features.
The soprano pipistrelle is very similar morphologically and was not even identified as a separate species until 1992. Now they can be told apart confidently in their hand, and with fair reliability acoustically as the soprano pipistrelle calls at 55 kHz compared with the common pipipstrelle at 45 kHz. In England, the soprano pipistrelle is often found associated with water and so it was no surprise to find them along the canal. An interesting observation however is that there appears to be much more activity to the east, near to larger water bodies. Denton Reservoir lies just beside the canal towards the eastern end and is likely to be an important foraging resource for this species.
The vast majority of the recordings related to these two pipistrelle species – the other bat species were found at much lower frequencies.
The noctule bat is our largest species and tends to fly high and early, often the first bat to appear around sunset and can be seen in the skies as the swifts are still on the wing. Only one noctule was heard during the transects, between Denton and Woolesthorpe and picked up again near Muston. This bat is large and the sky was light meaning I could watch it flying my way, foraging as it flew to the west. This is a widespread species which favours roosting in trees, but numbers are generally lower than the pipistrelles.
Brown long-eared bat
Brown long-eared bat is one of our quietest but most charismatic bats. Their large ears make them quite charming to behold, and they are frequently found roosting in barns and other buildings. I only picked up a single instance of this bat, but their very quiet echolocation means they are generally under-recorded.
The myotis bats are considered to be some of the most difficult to identify from sound alone. Daubenton’s bats are the myotis species most frequently associated with water as they specialise in flying low over still waters and taking insects on the wing or from the water’s surface. Natterer’s bat is another myotis species and some of the calls recorded along the canal in September are characteristic of this species. Whiskered and Brandt’s bats are the other two myotis species which are likely to be present in this part of the country. These two bats are very similar to one another and are difficult to separate even in the hand. Some of the calls have the characteristics of one (or both) of these two species. Whilst these species are not commonly associated with aquatic habitats, the canal also boasts hedgerows, copses and grass bank margins which provide great terrestrial habitat as well.
I encountered a whole host of other species whilst cycling along in the afterglow of sunset including barn owls, tawny owls, hares fleeing down the towpath and badgers snuffling in the hedgerows. The canal is stunning in the daytime but at night it comes alive with a whole host of new species – a walk around sunset might reveal creatures which you would not normally be privilegedenough to watch.
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.