Vegetation Layers in an English Woodland

The different layers within a woodland are one of those classic illustrations from ecology textbooks – usually a cartoon graphic showing how the structure changes as you move from the ground up to the canopy. The distinctions are indicative – there is often plenty of overlap between the layers – but these are a useful way of thinking about the woodland in terms of its ecological function beyond what simply meets the eye. Helping you to see the wood for the trees, if you will!

We undertake tree climb and inspect surveys for bats in a variety of settings – from individual trees in gardens to well-spaced parklands and dense woodlands. Each of these gives a different insight into vertical variation but a recent climb in an oak and ash woodland gave a nice opportunity to illustrate how this changes in a typical ancient woodland habitat.

English Oak Woodland Structure
Photographs taken at 2m (bottom), 6m (middle) and 12m (top) in an English oak and ash woodland to illustrate the variation in spatial structure.

The number of ‘layers’ and their distinctions vary between sources and across countries – I’ve seen three defined layers, nine defined layers and every number in between delineated in various graphics. I’m going to keep this simple and focus on the three broad categories which are shown in these photos:

Field Layer – taken at 2m height

Ground Layer
Photograph taken at 2m showing the field or ground layer in an English oak and ash woodland


This photograph encapsulates what could be considered the field layer, the ground layer or the forest floor depending on which divisions you use. Broadly, this is the view from the ground – the most apparent vista for most visitors to the woodlands but the scene varies greatly as the year progresses. In secondary woodland or more botanically diminished sites, this can be a mass of ruderals such as nettles, cow parsley and bramble whilst some plantation woodlands can be head-high in bracken. In ancient woodland – such as this – springtime sees a flush of ancient woodland species which time their flowering early in the season before the canopy closes overhead. As May arrives and the trees and shrubs come into leaf, the main event on the forest floor is already coming to an end. Some species flourish later in the season but in September, the vegetation has largely died back often leaving a relatively bare floor. The dominant vegetation remaining is therefore the trunks of the trees and the shrubs which rise above the field layer to leaf and flower higher.

Scrub Layer – taken at 6m height

Shrub Layer
Photograph taken at 6m showing the hazel-dominated shrub layer in an English oak and ash woodland

This could be described as the under-canopy, the scrub layer, the shrub layer or the under-storey layer. This is the level at which the shrubs flourish – those smaller woody species which often include hawthorn, blackthorn, hazel, holly, dogwood and elder, amongst others. These shrubs can often form such a dense canopy that the view to the treetops above can be quite obscured – something of an issue when you’re searching for bat roosts! In this instance, hazel and hawthorn dominate and as the photograph shows, they form a dense and highly cluttered environment some 6m above the ground.

Canopy Layer – taken at 12m height

Canopy Layer
Photograph taken at 12m showing the space between the shrub layer and the woodland canopy in an English oak and ash woodland

This is up at the top of the trees, where the taller trees branch and close their canopies to claim first use of the sunlight available. I’m not right in the canopy in this photograph – the trees did not require us to climb to the peaks – but this nicely illustrates the shrub layer below with the high canopy of the oak and ash above. In some forests, the species composition includes a sub-canopy of smaller trees – such as rowan, silver birch and field maple – which form a layer between the lower shrubs and the taller climax species. This photograph nicely illustrates how much of a space can open up between distinct layers within the higher reaches of the forest structure.

Why does it matter?

An appreciation of how the character and conditions of a woodland change on a vertical plane are just as important, although a little harder to appreciate, than the variation on the ground. The illustrations above are for just one section of just one woodland and each type of species composition but they help to give a visual idea of how this works.

One example of how this type of variation is important is when considering how bats might use a habitat. Different species of bat have different hunting characteristics and habitat preferences, and this often relates to how open or cluttered a habitat is. Species such as brown long-eared are highly maneuverable and will glean insects from leaves so a reasonably cluttered woodland environment suits them perfectly. At the other end of the spectrum, a noctule hawks in open space, often flying over fields and catching its prey on the wing. Species such as pipistrelle are typically characterised as edge specialists which forage along woodland edges, hedgerows and other similar environments.

Pipistrelle bats are typically described as ‘edge’ species which forage along the edges of vertical features, such as a woodland edge

The field layer of the woodland looks ideal for a species such as brown long-eared but you might think that it would be too cluttered and enclosed for other species. However an insight into the structure above the shrub layer reveals a mosaic of open space and leaf cover which provides perfect ‘edge’ habitat for a hunting pipistrelle, and the voids between the trees would be perfectly navigable for a noctule in search of a roost. This was the subject of a talk by Ian Davidson-Watts at a recent BCT Bats and Woodland conference which you can read more about in this blog post here.

If you’re looking for tree climb and inspect surveys for bats, do check out this page for further details!



Easegill Caves Hibernation Surveys

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!



Life after Light – Bats along Grantham Canal

It’s very nearly Halloween – what better time to introduce you to the bats which haunt Grantham Canal when darkness falls…

IMG_4159I 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.

Common Pipistrelle

The Common Pipistrelle is one of the smallest but certainly the commonest bat species in the UK
The Common Pipistrelle is the smallest and the commonest UK species

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 orange bat symbols in this map indicate the locations where common pipistrelle bats were identified. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent
The orange bat symbols in this map indicate the locations where common pipistrelle bats were identified. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent

Soprano Pipistrelle

The soprano pipistrelle is physically similar to the common pipistrelle but a has differences in morphology such as wing veination and face colouring with the much darker face of the common pipistrelle earning it's other name of bandit pipistrelle
The soprano pipistrelle is physically similar to the common pipistrelle but has differences in morphology such as wing veination and face colouring with the much darker face of the common pipistrelle earning it’s other name of bandit pipistrelle

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 blue bat symbols in this map indicate the locations where soprano pipistrelle bats were identified. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent

The vast majority of the recordings related to these two pipistrelle species – the other  bat species were found at much lower frequencies.

The yellow bat symbols in this map indicate the locations where Natterer's bats were identified; black represents whiskered/Brandts; purple represents brown long-eared; and green represents noctule. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent
The yellow bat symbols in this map indicate the locations where Natterer’s bats were identified; black represents whiskered/Brandts; purple represents brown long-eared; and green represents noctule. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent


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.

Noctule bat - the largest UK species
Noctule bat – the largest UK species

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 brown long-eared bat is named for quite obvious reasons!
The brown long-eared bat is named for quite obvious reasons!

Myotis bats

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.

A Daubenton's bat - the myotis species most frequently associated with water. The myotis bats are larger than the pipistrelles but not as big as the noctule.
A Daubenton’s bat – the myotis species most frequently associated with water. The myotis bats are larger than the pipistrelles but not as big as the noctule.

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 privileged enough  to watch.

Sunset along Grantham Canal

If you are looking to commission bat surveys in the Midlands area, check out Landscape Science Consultancy’s website here!

Midlands Bat Conference 2014

The Bat Conservation Trust runs an annual Bat Conference in September each year which is attended by bat groups, enthusiasts and professionals from around the country. They also hold regional conferences once every two years and this year’s Midlands conference was at the end of April. The focus of the conference is not exclusively based in the region, but has talks from local bat group members and researchers as well as spotlight talks from the various bat groups in a region so that neighbouring groups can find out about projects which others in the area are involved in.

Morgan Bowers talking about the Brumbats Flight Cage at the BCT Midlands Bat Conference 2014 (image borrowed from the BCT Twitter feed)
Morgan Bowers talking about the Brumbats Flight Cage at the BCT Midlands Bat Conference 2014 (image borrowed from the BCT Twitter feed)

The Warwickshire Barbastelle Project

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.

Emergence behaviour of Natterer’s and brown long-eared bats

Rachel Fryer gave a talk on the emergence behaviour of Natterer’s and brown long-eared bats. She observed two known maternity roosts once a week between May and September and recorded each emerging bat to identify the earliest emergence time, the median emergence time and the number of bats emerging, and correlated this with environmental variables. The earliest emergence times proved interesting with records earlier than the textbook examples. The median emergence time for Natterer’s was 60-64 minutes after sunset whilst brown long-eared bats left a little earlier with a median emergence time of 44-49 minutes after sunset. The number of bats emerging were found to fluctuate between nights – this could relate to some bats remaining in the roost or the colony being split between different roost sites. However, there was a correlation between the number of brown long-eared bats emerging and the average wind speed with fewer bats emerging on windier nights. The light levels also seem to influence emergence behaviour with brown long-eared bats emerging later under higher light levels; and Natterer’s bats emerging earlier when there was higher cloud cover. This empirical information on the emergence characteristics is valuable as existing published information is often sparse and often doesn’t specify whether the time relates to the earliest or the median emergence time.

Species Distribution Modelling for Bechstein’s Bats

A talk given on behalf of Lia Gilmour from the University of Bristol shared the results of Species Distribution Modelling of Bechstein’s bats and the use of the results to identify further suitable habitat for this rare species. The principle behind this modelling is to look at the conditions in which the bats are found and identify further locations where these conditions are present. In theory therefore, if the SDM is modelling correctly, the bats may be found in these locations. This model found four key variables which appeared to be important: the presence of broadleaf/mixed woodland, a relatively low summer rainfall, a minimum January temperature of >7 degrees and a relatively high temperature range. This corresponds well with the southern distribution of this woodland dwelling bat. The model appeared to work well as new records were found to fall within the optimal or marginal suitability distributions predicted by the model. This is a valuable tool in targeting the search for further Bechstein’s colonies to those locations where the bats are most likely to be found. It will however only identify further habitat like the ones in the bats are known to dwell and so new colonies may still be found in unexpected locations outside of the current or accepted range. This problem is further exacerbated for the Bechstein’s as so much of the distribution is known from targeted surveys using acoustic lures to capture and identify the bats. These surveys were largely carried out in locations where the bats were most likely to be found – specifically broadleaf woodland sites in the south of the country and this will have influenced, in turn, the predictions of the models. It is a case of don’t look; don’t find and the risk with this approach is that more borderline sites may be overlooked if the limitations of the methodology are not appreciated.

Alcathoe Bat in the UK

Phil Brown has been undertaking research using DNA analysis of small myotis species bats. A cryptic species was recently identified in 2010 called the Alcathoe bat which is very similar to Brandt’s and Whiskered bats and, whilst known on the continent since 2001, was not known to exist in England. One of the aims of Phil’s research was to see whether these bats could be identified outside of their current known range of Sussex, Surrey and North Yorkshire. 70 sites were surveyed and 395 bats were caught of which 39 were whiskered/Brandt’s/Alcathoe (WAB). This targeted capture and DNA collection was supplemented by samples sent in by other bat workers around the country with the result that a total of 110 WAB samples were tested. 95 of these were found to be whiskered bats; 10 were found to be Brandt’s bats; and 5 were found to be Alcathoe. Sadly, these five bats were all found in Sussex/Surrey and so there remain no records in between their current known locations towards the north and south of the country.

Brumbats Flight Cage

Morgan Bowers from Brumbats gave an inspirational and enlightening talk on the new flight cage they have had built. This allows the bat carers to assess the health and abilities of rescued bats, gives the bats opportunity to exercise and to behave in a more natural manner, and allows them to be rehabilitated and soft-released with a more supportive environment if they take a little longer to build their abilities. This also saves the perennial bat carer issue of bats getting loose in the house and hiding in the most unlikely places – including inside a hoover! The flight cage is a good training tool as well as it offers a safe environment for new bat carers to learn their rehabilitation and handling skills. You can find out more about the flight cage here with some videos to watch too! Another blog on the conference can be found on the Brumbats page here.

White Nose Syndrome in the UK

The last talk of the day was given by Alex Barlow on White Nose Syndrome in the UK. This is a devastating disease in the USA which has seen mortality rates in hibernation sites of 97% for the little brown bat and 49% for the big brown bat. The syndrome is caused by a fungus which infects the bats and gives a characteristic white nose where the mycelium grows. The presence of the fungus leads to increased evapotranspiration and loss of electrolytes which effectively dehydrates the bat and it rouses out of torpor to drink – some bats have even been observed trying to eat snow. The survival of a bat through the winter is a finely balanced process and this wakening uses a large amount of the winter reserves of the bats which then can not find food to replace the energy they have lost. There were serious fears that this disease may spread to other locations but surveys and sampling across Europe have found the fungus but have not recorded any associated mass mortality events. DNA analysis of the fungus has found significant genetic diversity in Europe which suggests that it is endemic to the continent, whilst those in the USA are all genetically similar, suggesting it is a recent introduction. This may mean that the European bats have co-evolved alongside the fungus and will therefore be able to cope with it, whilst it is a novel pathogen to bats in the US and they have suffered badly from its effects. Further active surveys for the fungus are taking place through 2013/14 with 25 sites selected across the UK, especially those used for tourism or caving. The current state of knowledge allows us to be cautiously optimistic that this fungus should not lead to the same level of devastation in the UK as has been seen in the US.

Spotlight Talks on Local Bat Groups

The spotlight talks from the local bat ground included Lincolnshire all the way across to Warwickshire, Worcestershire and Derbyshire taking in Leicester and Rutland, Nottinghamshire and Birmingham and the Black Country on the way. A range of projects are underway including NBMP monitoring of roosts; the Nathusius pipistrelle project for which Nottinghamshire and Derbyshire are amongst the pilot groups; the BrumBats Batlas project which aims to extend their knowledge of bat distribution across the area; and a range of public engagement events including bat walks and talks. For more information on the activities of all of these groups, check their pages which are all linked above. Whatever your level of interest, there will be something to get involved with wherever in the Midlands you are!

BCT Artificial Light and Wildlife Symposium 2014

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:

#1 Artificial lighting increases globally at a rate of 6% per year;
#2 There are 7.4m street lights in the UK and;
#3 20% of UK energy expenditure goes on lighting.

Variations on this photograph - a satellite image of the earth at night showing the extent of artificial lighting - was 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.
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

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.
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.
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!

Bat Swarming Site – first trial of Bushnell Trail Cam

My last professional bat survey of the season was completed last week – at a railway tunnel which is a swarming site for a small number of bats. Swarming sites are locations, often caves, mines or tunnels, where bats – particularly the myotis species – gather in the autumn to mate. We stayed until 5h after sunset to monitor the usage of the tunnel and recorded around 5-6 bats at this site. They are most likely to be Natterer’s bats, judging by the calls, although myotis species are notoriously similar acoustically, and can be difficult to tell apart from sound alone.

This is an extract from the echolocation files from the tunnel survey. The calls which are very long and straight (known as FM of Frequency Modulated calls) are distinctive of myotis species. This is probably Natterer's bat because the start of the call is at such a high frequency and the end is at such a low frequency. For reference, most people can hear upto about 18 kHz which would be a very high pitched sound. These calls are from well above 100 kHz and end around 30-40 kHz.
This is an extract from the echolocation files from the tunnel survey. The calls which are very long and straight (known as FM of Frequency Modulated calls) are distinctive of myotis species. This is probably Natterer’s bat because the start of the call is at such a high frequency and the end is at such a low frequency. For reference, most people can hear upto about 18 kHz which would be a very high pitched sound. These calls are from well above 100 kHz and end around 30-40 kHz.

The bats were using the tunnel entrance – a great, ominous opening onto blackness surrounded by shrubs and trees – but they spent most of their time flying in tandem within the tunnel and especially around the vertical air vents – circular ‘chimneys’ some 5m wide – which are spaced out down the length of the tunnel.

I’ve recently bought a trail cam and this seemed like a good opportunity to try it out and answer the first question – can it be triggered by bats? I’ve spoken to people who have said that they can, but that the lag between the detection and the shutter closing means that the bat has been and gone before you can get a good photo.

I’ve opted for the Bushnell Trophy Cam Max HD, largely because of the no-glow LED’s which would hopefully reduce the risk of it being spotted and interfered with, but I wasn’t sure how the different cameras available would compare on their sensitivity. It can certainly spot a greenfinch hopping about on the lawn which suggests it is reasonably sensitive to small creatures, but my first test on bats suggested that flight ~6m away was not detected.

I placed the trail cam face-up beneath one of the air vents and there were no ‘triggers’ but I also used the ‘field scan’ setting to automatically take a 10 second video every 5 minutes, regardless of whether the camera detected something to monitor. The result was lots of empty shots, with only dripping water to reveal movement, but I did record one brief pass of two bats flying close together. It’s not great footage – very far from something you might have seen on the BBC recently using their high quality night vision kit – but it is enough to show that the bats are there and it could potentially be a way to monitor the presence of bats in a site such as this over a period of time.

The use of automated bat detectors has really taken off in recent years – this is a great supplement to surveys where ecologists walk or watch and detect bats using hand held devices. A static unit can sit in the field for a week, record every bat which goes past, and be picked up and analysed at your convenience. It lacks the qualitative element which can be gained from an actual surveyor in the field – where did the bat fly, which direction, what behaviour – but it is invaluable to assess the assemblage of bats present, picking up species present at low densities or passage use by rarer species.

In a similar way, I am hoping that the trail cam will be a great way to gather a census of the species of mammals in an area or at least using a trail, even if they only pass that way once a week. With any luck, watch this space for further updates and footage which are hopefully a little better than this!


If anybody has any experience of catching videos of bats in flight using a trail cam, I’d love to hear about it!

BCT Bat Conference 2013

This year’s National Bat Conference, organised and run by BCT, was at Warwick University last weekend. The conference is always held in September and I always come away with a mixture of enthusiasm and regret – it’s a great opportunity to chat to other bat workers, both volunteers and consultants, and listen to some fascinating talks which really inspire you… but it is held just as the main bat season is drawing to an end and there is little time left to go out and carry out the surveys which the conference inspires! I have certainly come away with a few ideas for next spring.

Serotine bat in the hand

Several of the talks this year could be grouped broadly into the ‘state of bats’ category. This included the opening talk by Julia Hanmer, the chief executive of BCT, who outlined the work which BCT have undertaken in the last year with a special focus on the work being done to help churches with bats find solutions which allow both to coexist. Lincolnshire Bat Group’s own work in Tattershall Church was held up as a particular example of how the bats could live happily alongside the congregation with input and guidance from experts and this topic was taken up and explored in more detail later in the programme by Laura Bambini who has been been working alongside church wardens and congregations to find out the ways in which bats do genuinely impact upon the running of a church, and what information and support can be provided to alleviate these concerns. This positive work was set sadly against a backdrop of the general anti-environmental ethos of the current government, with Owen Patterson’s name being rightly greeted with boo’s and hisses by a conservation-minded conference congregation. The fact that the Chief Constable who leads on Wildlife Crime is openly anti-bats was another shocking revelation and goes to show just how much prejudice we need to work against.

Pete Charleston heads up the BCT investigations unit and took the stand for the next talk. BCT and Pete in particular are doing great work to combat wildlife crime relating to bats, with regular increases in numbers of referrals and numbers of prosecutions. We are sadly let down at present however by the prosecutors themselves; a recent case where a developer knowingly destroyed six bat roosts and was fined just £35 per offence is grossly disproportionate to the crime committed and serves to send out entirely the wrong message to those who view the protection of our native wildlife as an impediment to their own economic gains – a mantra perpetuated by George Osborne in his recent attacks on protected species legislation.

Leaving politics aside, and on a much more positive note, Lisa Worledge and Helen Miller gave a talk later in the morning on the current research on Pseudogymnoascus destructans in Britain and Europe. This is the fungus responsible for the deaths of huge numbers of bats in hibernation roosts in the USA and there is a fear that the pathogen could cause similar destruction to our native species. The talk concluded that there was cause for cautious optimism that the bats in the UK had in fact co-evolved alongside this fungus and were therefore relatively unaffected by it. The basis for this is the identification of the fungus in environmental samples from across Europe and in the majority of hibernation sites surveyed in the south of England in a recent pilot study, as well as the positive identification of the fungus on a hibernating bat for the first time in the UK, yet without seeing the same devastating effects which are associated with the fungus in the US. The genetic diversity observed in the fungus across Europe suggests that the pathogen has been present and has developed into differing genetic strains across its range, whilst the homogeneity of the fungus genome in the USA suggests a much more recent introduction. The fact that this fungus appears to be novel in the USA would explain why the bats there are being so badly affected in the same way as a new flu strain can strike down half the country. The risk of the disease blighting our UK populations has been cause for concern for a number of years now, and cautious optimism is certainly a better outlook!

The importance of bats within an ecosystem, and the risk of losing such an important species, were highlighted in a talk by Ryszard Oleksy who has been undertaking work on the role of the Madagascar flying fox on forest regeneration in Madagascar. This is a large fruit-eating species, very different to our tiny insectivorous UK species, but the importance of the genera on an ecosystem scale is likely to be similar. The study found that 110 plant species are included within the diet, that seeds which have passed through the digestive system germinate well and that the distance which an individual bat can disperse seeds is significant. The species makes a very effective agent of forest regeneration, linking up isolated forest patches in a fragmented landscape and assisting in the dispersal of a number of endemic plant species.

One issue which is well known to most bat workers now is the risk which breathable roofing membranes (BRM’s) pose to bats roosting within buildings. Bats can easily become entangled in many of these membranes and there are reports of over 100 bats being killed by becoming trapped and dying of dehydration or exhaustion, and yet they are put into new roofs on an almost routine basis, including roofs where known roosts may be present. Stacey Waring gave an excellent talk on her research into this issue, combining a more abstract lab-based tests of the extent to which different membranes on the market become ‘fluffy’ and as such, of risk to bats; with tests of how the membranes performed with captive bats within a rescue centre. All of the membranes tested were found to pose a risk, compared with traditional bitchumen felt, although there is hope that the findings of this study may feed into the design process and more bat-friendly materials may become available in the future.

Geoff Billingham gave a talk on Wolvercote Tunnel in Oxford, outlining the results of a range of surveys and a concept of mitigation designed to ‘flush out’ bats from the tunnel in advance of an oncoming train to avoid them being killed. This relied upon lights being turned on in the centre of the tunnel a few moments before the arrival of a train, and then progressing out to the peripheries with the hope that bats would move ahead of the advancing light. The most concerning figure within this talk, to my mind, is the 5 dead or grounded bats identified in 21 visits to the tunnels. Trail cameras also identified an average of three visits per night from species such as foxes or cats, which would scavenge a bat carcass, making it unlikely that a dead bat would remain for a long time. This rate of killing is significant, considering that the tunnel is 130m long, the trains run at 30mph and they do not run much beyond 10:30pm. If this number of bats are killed in a single tunnel, the number which must perish across the country is highly significant and is likely to have a serious impact upon populations. It also puts into perspective the potential impact of new technologies such as wind turbines, when viewed in comparison with more established and accepted threats which may be of much greater significance.

Four talks over the weekend discussed the ways in which we can increase our knowledge of the distribution of bats within the UK.

Two focussed on islands – the first of these was studying the distribution of rare woodland bats, specifically Bechstein’s and barbastelle – on the Isle of Wight. Ian Davidson-Watts sampled in 42 different woodlands across the island and used mist nests and harp traps to catch bats and radio-tag them. Two thirds of the woodlands were found to have Bechstein’s present – this is one of the Myotis species and one of the rarest species in the UK – and a number of maternity roosts were subsequently identified. The surveys also identified potentially the largest barbastelle roost within the UK with over 115 individuals counted out. These findings make the Isle of Wight of potentially international significance for rare woodland bats at a landscape level.

Moving to the opposite end of England, Hugh Watson discussed static detector surveys on three islands off the Northumberland Coast to identify the species present. This is an under-recorded area and a total of five species were recorded on the islands with evidence of bats commuting to forage from the mainland.

Two further talks discussed mass-participation bat surveys where a large number of the general public were encouraged to get involved, to learn more about bats and to extend the coverage of bat records within a county.

The Norfolk Bat Survey set up a number of ‘Bat Monitoring Centres’ across the county so that everybody was within 15-20 miles of a station. The public could sign up for the survey and then pick up a static detector which would be put out at a number of locations within a 1km square and left to record the bats which went past. This has enabled bat records to be obtained for a large area of the county, and allowed interested individuals to find out which species fly through their gardens and their local landscape when darkness falls.

The Somerset Bat Group by contrast have designed their Big Bat Survey – a number of transects across landscapes within the county, including the Blackdown Hills and the Mendips, where a group of at least four people would be equipped with bat detectors and would walk the set routes to find out which species were present. Fifty and seventy members of the public took part in the respective surveys, and the results were again invaluable in increasing the knowledge of both the distribution of species within each area and their use of the various habitats present.

The last two talks focussed on technological advances in our approach to bat surveys. The first of these was a talk by John Atanbori of Lincoln University who is using computer vision techniques to automatically pick out bats from a video taken in low light levels and compute metrics such as wing beat frequency, with an aim to using this as a tool for species identification. The characteristics of bats in flight differ between species to a greater or lesser extent, as anybody who has watched the rapid wing-beats of a foraging pipistrelle alongside the broad-winged fluttering of a brown long-eared will know. The project is a work-in-progress but offers a fascinating new avenue of species identification if it can be developed.

The final talk was given by Ian Agranat of Wildlife Acoustics on their latest classifiers for UK bat calls. The aim of this software is to identify a bat call to species level (or genus level in the case of the myotis bats) without a bat worker needing to scan through every single call. The need for this technology is increasing as the price, availability and usefulness of static bat detectors is growing – these provide very cost effective monitoring of a site compared with human surveyors, but they do produce huge amounts of data which needs to be sifted through. The Wildlife Acoustics technology uses machine learning where a large number of identified calls are fed into the software and the algorithms identify differences which split the sound files up by their respective species. This is successful at an 80% accuracy which would significantly speed the process of analysis, whilst still at this stage requiring a certain level of operator confirmation and amendment. It is another exciting avenue of development and another ‘watch this space’.

Workshops were wide-ranging as usual and it is always a shame that you can only pick one or two. I opted for the tree roost field survey workshop with Henry Andrews taught me a number of new things as well as re-enforcing many others with examples and photographs which were invaluable, even after a summer spent up trees and inspecting potential roost sites. In case you haven’t come across his Bat Tree Habitat Key – you can view it for free on his webpage. The key to extending and refining this already invaluable piece of work is to gather more records – calling anybody working on bats and trees to contribute! On the Sunday I opted for Jon Whitehurst’s talk on an Introduction to Species Distribution Modelling – a last minute switch but one which has me itching to try out the techniques he outlined to model bats’ use of the landscape.

As I said at the outset, the only downside to the conference to my mind is that it is at the end of the season and so all of these great ideas and enthusiasm to get out there have to lie dormant through the winter until the spring when the bats come out of hibernation and the survey work can begin again.
Next year’s conference is due to be held at Warwick University again and you can find out more on the BCT’s website here and the BCT blog on the conference proceedings is to be found here. There are photographs from the conference on the BCT’s facebook page here, including the customary after-dinner Ceilidh!

An olinguito for the UK? The age of discovery is not over yet.

Scientists have just announced the discovery of a new carnivorous mammal in South America, named the olinguito. It is a member of the raccoon family and is the first new carniverous mammal to be discovered in the western hemisphere in 35 years.

Two of the reasons cited for the ability of the olinguito to evade description for so long is its habitat and behaviour – it lives in the cloud forests of Columbia and Ecudor and spends its time in the canopy where the dense mists conceal it, moving only at night. The team leader Kristofer Helgen said that ‘the age of discovery is not over’. Whilst this statement may seem plausible in tropical rainforests where great expanses of inaccessible habitats could conceal new species, you would be forgiven for assuming that the stable of mammals in the UK is… stable! For starters, this is one of the most densely populated places on the planet; then take into account the huge number of amateur naturalists, both past and present who dedicate their time to studying their local patch or favourite taxa; and then there is sad fact that we are really rather poor in mammalian fauna, having exterminated anything which might compete with us hundreds of years ago.

But there is one group of species which can still turn up surprises, even now. Bats share some of the characteristics of the olinguito which have allowed it to remain a mystery until now; that is they emerge at night, concealed by the darkness and move around on a plane above our own. Other characteristics condusive to crypsis include their habit of roosting in crevices and cracks, deep in tree cavities or high in caves, and their communication in ultrasound, so that only the low frequency social calls, or the echolocation of noctules, can be heard without a detector to convert the sound down into our range.

In 1993, it was first suggested that the pipistrelle bat, our most common species, actually comprised two cryptic species, the common and the soprano pipistrelle, the latter so named because the frequency of its echolocation is at a higher pitch than the former. Although these two species are similar, they can be quite easily told apart with characteristics such as wing veination, the presence of a ridge on the nose, the colour of the face and the difference in smell. If these two species were – say – butterflies, it is almost without question that they would have been separated as distinct species many years ago, but our most common bat escaped such detailed scrutiny as recently as 20 years ago.

In 2010, the presence of another cryptic species was discovered, the Alcathoe is a small myotis species alongside the whiskered and Brandt’s bats. This was not a new species – it is well known on the continent – but nobody realised that populations existed in this country as well. Work is still ongoing to establish just how widespread this species is and Philip Brown of Bristol University is asking anybody undertaking trapping work to describe any small myotis bats caught and send the details, along with droppings, to him to try to describe more fully and understand more accurately the status of this species in the UK.

The Nathusius pipsistrelle is a species which was previously thought to be a migratory vagrant but was first confirmed breeding in the UK in 1997 and its range within the UK has expanded year on year, partly as a result of increased survey effort but also believed to be a response to climate change as identified in this paper by Lundy et al. from 2010. This is a highly mobile species which is easily able to adapt to changing conditions and its increasing prresence in the UK is consistant with a continental scale change in range. The Bat Conservation Trust (BCT) run a Nathusius pipistrelle monitoring scheme in september every year – this is the month when the UK population is at its peak when bats arrive from the continent. If you would like to get involved with the surveys, you can find out more and sign up here.

There are a number of other species which are currently recorded as vagrants in the UK but it is possible that some of these may be resident now or may become so in the future as a result of climate change. These include the Kuhl’s pipistrelle and the parti-coloured bat – you can find out more about them in this factsheet from the BCT.

Bats are studied mainly through their echolocation using bat detctors, by observing them in flight when emerging from or re-entering a roost or commuting and foraging in the wider environment. This generally requires specialist kit to determine which species is being observed and despite the abundance of volunteers and professionals, the proportion of the population who would be able to identify bats, compared with those who could identify common butterflies and garden birds, is very low. Even more rarely are bat workers able to catch and inspect the bats they study, and even then it is possible that unusual bats may be regarded an unusual specimen of a known species rather than something otherwise unknown such as the Alcathoe.

The increasing ease with which DNA samples can be analysed may help to identify new cryptic species or confirm the presence of continental species within the UK which the progression of climate change may encourage.

Since 1993, we have identified two new species of pipistrelle to be resident in this country and there is the possibility of a fourth species joining the line-up in the near future. South America may have a new species of carnivorous mammal, but the best bet for the next new British discovery has to be within the bat world.

February Hibernation Survey at Harlaxton

Last Sunday was one of those beautiful days when everybody feels spring is just around the corner. The garden was filled with birdsong and sunshine, neighbours decided it was finally time to venture out and sweep those autumn leaves, daffodil bulbs bulged yellow at their tips where flowers are just waiting to appear.

What better day to descend into a sealed up tunnel, feeling the temperature drop steadily on a headlamp-lit thermometer, to search for hibernating bats!? Along with another member of the Lincolnshire Bat Group, we gallantly left the sunlight behind to see what we could find.

Entering the tunnels

In the past we have come across hibernating barbastelle bats, a rare species in the UK and here, at almost the northerly limit of their range, but sadly this time they were absent from the deep cracks which staircase down the brickwork where the tunnel curves.

Several years ago the Bat Group put up boxes in the tunnel, to provide a greater range of roosting opportunities and in here we did find some bats – two boxes had brown long-eared bats sleeping soundly inside, their long ears tucked behind their wings with only the tragus – the fleshy projection within the ears – apparent.

Hibernating brown long-eared bat

Only one of these bats was present during the January survey which means that some time in the last month, the other has flown and found this as a new place to enter torpor. This is not uncommon, bats will rouse during warmer winter weather and will often feed briefly before returning to their torpid state.
Along with the bats were around 60-70 peacock butterflies, all with their wings tightly closed and apparently oblivious to our torchlight as we passed by, careful not to disturb them. Many had damaged pieces of wing from last year – the first butterflies of the year are often tattered old veteran tortoiseshells, peacocks and brimstones.

Hibernating peacock butterflies

A number of herald moths were also present, including the pair pictured below who appeared to be hibernating upon a spiders web! I would love to hear any feedback on this interpretation – I do not think they have fallen prey to the spider as this same pair were present last September when I checked the boxes were ready for the winter and are apparently still alive and well! They will take flight when the weather warms, sometime between March and May.

Hibernating herald moths

If you are interested in joining the local bat group, visit their webpage for details – there are events throughout the year that you can take part in. For details of your local group if you are outside of Lincolnshire, the BCT webpage has all the info.

What do you need to climb-and-inspect trees for bats?

I have put this post together as a brief guide for anybody wanting to know more about what is required to climb and inspect trees for bats. When I was looking into the requirements, I couldn’t find anything which simply set out the steps so I hope this will be useful!

Climber in an oak treeTrees can be difficult to assess for bat roosts. Sometimes you can spot a feature – a woodpecker hole, split or fissure for example – which you can identify with reasonable confidence as a bat roost, perhaps by signs such as scratch marks, fur rubbing or droppings. But, in my experience, these types of features are the exception. You are much more likely to spot, what Henry Andrews would call, PRF’s or Potential Roost Features – see his website here for perhaps the best resource I’ve come across dealing with the use of tree roosts by bats.

You might want to be have more confidence in your assessment for a range of reasons; perhaps as a local bat group simply gathering data on local roosts, perhaps as part of research into bat distribution or movement, perhaps to protect the bats for example if the tree is dangerous and must be removed.

There are two approaches that can then be taken. Firstly, you could carry out a dusk/dawn emergence survey to watch for bats leaving or returning to a roost. This is quite labour intensive and has a number of limitations, such as the difficulty in being confident that a bat appeared from a particular location and the transient use of many roosts providing little confidence in a negative result. A second option is to inspect the feature closer up, using an endoscope perhaps to look within and see whether there are any bats residing within and whether the feature is actually as suitable as it may appear from the ground.

In order to carry out this “climb and inspect”, you will need two things:

Firstly, a licence to disturb bats with a handling endorsement. This is because bats are legally protected under both domestic and European legislation and it is an offence to intentionally or recklessly disturb them in their place of rest. See the BCT website for more info. This licence requires a large amount of specialist knowledge and experience of bats and their roosts. If you are interested in gaining the experience and, ultimately the licence, getting in touch with your local bat group is the best place to start. If you are already working in a professional capacity, I can highly recommend the Bat Licence Training Course run by Richard Crompton and Sandie Sowler.

Secondly, you need the competence and equipment to safely ascend to the feature. The basic qualification for this is the City and Guilds CS38 – Tree Climbing and Aerial Rescue Operations course. This not only teaches you the basics of climbing but also how to rescue somebody from a tree – if an accident does occur, it is critical that you know how to safely bring somebody down to the ground where they can be treated. This is usually a week long course which takes you through the principals, the theory, the legislation and the best practise for tree climbing before teaching you the practical techniques of climbing. At the end of the week, there is usually a separate assessment taking several hours where your competence will be assessed. As well as the climbing technique and principal, there is a requirement to identify a range of common tree species so this is something to brush up on beforehand. Another hint – you will probably not need to spike up trees for climb-and-inspect work, this is damaging to the trees and is only to be done if you are an arborist who is going to take the tree in question down (or in an emergence rescue situation).

Once you are qualified to climb, there are a few more things you will need before you can start:

1) The climbing equipment. The basic kit consists of a harness with leg-loops, rope, prussock cords, caribinas and a secondary support strop. These must all conform to the minimum legal requirements.
2) The safety equipment – this includes a helmet with a chin-strap, a knife with a retractable blade, a first aid kit and sturdy (steel toe) boots. High visibility jackets are also useful, especially for a groundsman. See point 3…
3) A groundsman! If something happens in the tree, you must have somebody with you who is qualified to climb and perform an aerial rescue. This might be required is for example there is a problem with your equipment meaning you can’t descend upon it, or if you were to hit your head and become unconscious. You should only ever climb if you have this second qualified climber on the ground the entire time that you are in the tree.
4) The kit to inspect the feature – an endoscope is either an eyepiece or, commonly now, a screen attached to a fibre-optic snake which allows you to see around corners and in deep, dark cavities of trees where bats might be hiding. This has the potential to cause disturbance to bats which is why the relevent licence and experience are critical. Other pieces of kit which might be useful include binoculars, a torch and a mirror!

If you were climbing for your own pleasure on your own land, this may be all that you require. However, if this is being undertaken in any kind of professional capacity, you would also need the appropriate insurance in terms both of personal safety and public liability.

For more information on the assessment and CS38 qualification, you can see the assessment criteria provided by NPTC here.

I work for a local Ecological Consultancy based in Grantham and we do offer professional climb and inspect services in the East Midlands area and beyond – if you would like more info then drop me a message and I will get in touch with you!

Potential Roost Feature (PRF) worthy of closer inspection!
Potential Roost Feature (PRF) worthy of closer inspection!