1 1 INTRODUCTION This paper has been prepared to support a ...

Berücksichtigung von Fledermäusen bei der Straßenplanung 

Fachgespräch am 24. Juni 2010 in Köln 

Erfahrungen mit dem Fledermausschutz im Zuge von 

Straßenbaumaßnahmen im Vereinigten Königreich 

Experiences of Dealing with Lesser Horseshoe Bats (Rhinolophus hipposideros / Kleine Hufeisennase) 

in Wales, United Kingdom, Len Wyatt, Welsh Assembly Government 

1 INTRODUCTION 

This paper has been prepared to support a presentation to the Bats and Road Planning 

event held on 24 June 2010 in Cologne, about the work of the Welsh Assembly Government 

for Lesser Horseshoe Bats (Rhinolophus hipposideros / Kleine hufeisennase). 

The Welsh Assembly Government is responsible for the improvement, operation and maintenance 

of the motorway and trunk road network in Wales. 

The information in this paper relates to large scale new road infrastructure, rather than small 

scale projects or maintenance operations. 

Its purpose is to: 

• Explain the context in which the Welsh Assembly Government has been carrying 

out its work 

• Provide information on some of the mitigation measures for Lesser Horseshoe 

Bats which have been carried out by the Welsh Assembly Government 

• Provide principles which have informed the way we have considered these 

bats in our work 

• Provide sources of further information from the UK 

It should be noted that the information and mitigation measures described in this paper, may 

not apply or work in other situations where the context of the landscape, project details; or 

behaviour of the same or other species of bats is different. 

2 CONTEXT 

UK Population 

The lesser horseshoe bat population of the UK is estimated to be around 15,000 – 24,000 

individuals concentrated in the south and west of the UK. About half of that population is believed 

to be resident in Wales. Up to 2008 the population in the UK is believed to be increasing 

overall. Figures for 2008 onwards are currently not available. 

Overview of Lesser Horseshoe bat ecology in UK 

In the UK the following features can be used by Lesser horseshoe bats. 

1. Summer/Maternity Roosts: 

Used during late spring, summer and early autumn. Usually found in: 

• Buildings dating from before the 20 th Century with heated cellars, roofs, attics 

• Caves 

• Structures such as bridges with sufficient space and suitable temperatures. Lesser 

horseshoe bats cannot easily crawl into small space, so require larger entrances into 

roosts and a large space to fly around in before they come out to feed. 

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The largest maternity roost in Wales (before the arrival of pups) is currently c800 individuals. 

The sizes of maternity roosts close to our projects range from around 10 to 420 individuals. 

2. Hibernacula: 

To enable hibernation from winter conditions and lack of insect prey. Usually found in: 

• Caves 

• Unheated cellars 

• Mines 

• Ice houses (houses built to store ice during the summer) 

• Tunnels 

Lesser horseshoes will forage relatively close to the hibernacula in winter if temperatures are 

warm enough and food is available. It is important to realise that hibernacula can be up to 

20km away from the summer/maternity roost. Some summer/maternity roosts can be used 

during mild winters. There is currently no evidence that the bats migrate within or to/from the 

UK to avoid winter weather. 

3. Night Roosts 

These are locations used by individual or small numbers of bats as an occasional resting 

place between feeding: 

• Extensions on entrances to buildings (porches). 

• Cellars 

• Open buildings, sheds 

Exceptionally they can be found in: 

• 300mm drainage pipe under a single 

carriageway! (one record of one male 

found by radiotracking). Also used as a 

day roost. 

• Crevices in rocks (one record of adult bat 

entering a crevice during a radiotracking 

study in Mid Wales). 

Photo: checking crevices for bats in rock 

face. Jacobs. 

4. Habitats/features used to guide movements 

The following habitats/features can be used by bats to guide their movements: 

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• Well connected hedgerows 

• Well connected woodland edges 

• Rivers, streams and linear watercourses 

• Wire fencing/stone walls – occasional records. 

• Underpasses and tunnels 

Photo: automatic detector at culvert used by 

bats. Jacobs. 

5. Habitats used for feeding 

The following habitats can be used as feeding areas: 

• Broadleaved woodland and scrub, 

occasionally other types of woodland 

• Vegetated river corridors 

• Grassland/wet grassland close to flight 

routes or vegetation 

Photo: Landscape around Porthmadog. 

Maternity roost of 420 individuals next to road at 

bottom left. Halcrow. 

Lesser horseshoe bats prefer to eat: 

• Craneflies (Tipulidae) 

• Moths (Lepidoptera) 

• Midges/small flies (Diptera – nematoceran) 

There is currently insufficient evidence to confirm whether lesser horseshoe bats use specific 

areas in the autumn (known as swarming areas) to socialise like some other bat species. 

Legislative requirements 

The UK legislation, based on European Community Directives, requires the following to be 

undertaken: 

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• Creation, management and protection of internationally important (Natura 2000) sites. 

• Environmental Impact Assessment of relevant projects 

• “Appropriate Assessment”/Assessment of the Implications on European Sites (AIES) 

of relevant projects on Natura 2000 sites. 

• Strict system of protection of individuals and resting/roosting places against killing 

and disturbance. 

In addition, national legislation allows for the creation, management and protection of nationally 

important sites; and requires the conservation and enhancement of species within the 

legal powers available to carry out the work. 

This means that there could be a large number of legislative requirements to be met before a 

project can go ahead where lesser horseshoe bats are involved. 

Welsh landscape and lesser horseshoe bat distribution 

Wales covers 20,779 square kilometres. In comparison England covers 130,422 square 

kilometres. The central and northern western areas of Wales are generally dominated by 

mountains and hills, with river valleys cutting through them. (see map on Page 5). 

Broadleaved woodland and hedgerows can be prominent features of the non-urban lowland 

landscape. The main urban areas are concentrated in the coastal areas in the south east and 

north of the country. Built up areas in the other parts tend to be much smaller. 

Lesser horseshoe bat distribution in Wales is concentrated around North West Wales and 

the border areas with England in the South East. There are also smaller populations in South 

West Wales, Mid Wales and North East Wales. (See map on Page 6.) 

Welsh Assembly Government trunk road and motorway network 

The majority of our 1,700km network is located within rural areas. There are two Motorways 

(of four to six lanes of traffic) through south Wales (Annual Average Daily Traffic (AADT) in 

2008 13,000 to 105,000). The majority of dual carriageways (of four lanes of traffic) are located 

in south and north Wales. (AADT 2008 10,000 to 75,000). The network is predominately 

of “single carriageway” standard (with two lanes of traffic – eg: width of the carriageway 

without verges and hard strips is c7.3m (AADT 2008 1,600 to 17,000). 

In many areas the geology and landscape means that the network follows the river valleys, 

which also provide the best areas for lesser horseshoe bats. The map below shows the spatial 

overlap between the road network and lesser horseshoe bat areas. 

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Potential impacts of major road infrastructure 

In a recent strategic assessment of all of the Welsh Assembly Government’s proposed 

transport activities across Wales (including roads) the following potential impacts on three 

species of bats (including Lesser Horseshoe Bats) were identified: 

POTENTIAL IMPACT (project stage in which the impact may occur) 

• Habitat Loss/fragmentation including effects on foraging areas (construction) 

• Loss of breeding areas, hibernacula etc (construction) 

• Damage to flight lines between roosting/feeding areas (construction) 

• Changes to habitats used by species – changes to air quality, water quality and water 

flows (construction and operation) 

• Disturbance to species (eg: direct effects on roosts etc). (Construction) 

• Noise and vibration disturbance – changes in behaviour (construction and operation) 

• Visual and lighting disturbance – changes in behaviour (construction and operation) 

• Wildlife Vehicle Collisions (operation) 

• Climate change effects – changes in distribution (operation)* 

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*Climate change may increase the area of the UK suitable for the bats. MONARCH III 

computer based modelling completed in 2007 suggests that the climate space available 

may increase to the north and east. 

 

It should be noted that not all impacts are likely to occur in all situations, and for many projects 

the results of the Environmental Impact Assessment and “Appropriate Assessment” 

processes may conclude that certain impacts are not significant. 

One of the areas where our knowledge is not so good relates to the way Lesser Horseshoe 

bats fly over and around roads, especially as the bats have a number of flight characteristics 

which increase the likelihood of impacts on flight lines and potentially mortality caused by 

wildlife vehicle collisions. 

The following generalised flight characteristics can be identified from published texts and 

field surveys: 

• A reluctance to fly across open areas. However, the width of open area which the 

bats will refuse to cross, or cross less frequently, is currently unknown. 

• Avoidance of street lights and lit areas, although there is some evidence that the bats 

may tolerate some lighting in underpasses. The exact amount is currently unknown. 

Flying high over traffic height using tree canopies/crowns; or if tree canopies are not available 

between 0.5 and 1.5m above the road surface. Surveys have shown that removal of 

tree crowns or gaps in 

• canopies may force the bats down to travel at just above road level. The width of gap 

which causes this behaviour is currently unknown. 

• Flying up and down linear features on the roadside, but on the side away from the 

road. 

• Using the same routes to reach locations when vegetation is removed, or a road put 

across the flight path, until a decision is made to fly a different way. The length of 

time which needs to pass before a different path is chosen is currently unknown. 

Information on distances travelled by bats between roosts and feeding areas varies from 2km 

to 22km in one night depending on the age and sex of the bat. One male bat in North Wales 

has been recorded during a radiotracking study flying 4 times between a roost and hibernacula 

10km apart, in one evening. There is some evidence that while at the maternity roost 

females travelled between 2km and 5km to feed; and juveniles around 1km to 2km. 

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3 MITIGATION CASE STUDIES 

The following 11 case studies are provided to give examples of the more interesting mitigation 

measures which we have undertaken. There are of course other techniques available 

which are relatively common. 

The studies concentrate on the following potential impacts: 

• Habitat Loss/fragmentation including effects on foraging areas (construction) 

• Damage to flight lines between roosting/feeding areas (construction) 

• Wildlife Vehicle Collisions (operation) 

Case Study 1: A465 Heads of Valley Section 1 Abergavenny to Gilwern 

Potential Impact 

Context of the project 

Context for bats 

Description of measure 

undertaken 

Why undertaken 

Results of monitoring 

Habitat Loss/fragmentation including effects on foraging 

areas (construction) 

Widening of existing road from 2 lanes (single carriageway) 

to 4 lanes (dual carriageway). Open to traffic throughout 

construction period. 

Maternity roost of c90 individual bats within 300m of project. 

Bats regularly flew under and possibly over existing road at 

various locations to reach feeding and other breeding areas. 

Roost believed to be connected to Natura 2000 site 

2km away. 

Creation of lesser horseshoe bat feeding habitat from a 

grazed field, by slowing down of stream, excavation of 

shallow pond, managing grass area to be become more 

bat friendly (eg: allow flowering plants to flower before 

cutting) and planting of insect friendly shrubs and 

trees. 

Area: approximately 2.2ha 

Completed in 2008 

Concerns that mitigation measures elsewhere would not 

create enough mitigation to cover the significance of the 

effects, therefore decision made to create area between 

road and roost to provide a new feeding area. The location 

it was hoped would reduce the need for bats to cross over 

the road to feed 

Annual monitoring so far shows slow uptake in the use of 

the area for feeding (1 or 2 individuals per year from none 

at all). 

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Photograph: Excavating 

shallow pond. Jacobs 

Case Study 2: A465 Heads of Valley Section 1 Abergavenny to Hirwaun 





undertaken 

Damage to flight lines between roosting/feeding 

areas (construction) and Wildlife Vehicle Collisions 

(operation). 

Widening of existing road from 2 lanes (single carriageway) 

to 4 lanes (dual carriageway). Road above 

open to traffic throughout construction period. 

Maternity roost of c90 individual bats within 300m of 

project. Bats regularly used the existing vehicular underpass 

at Hopyard (4.2m high, 3.5m wide, 18.5m 

long) – c 120 - 200 individual movements recorded 

over one night. Roost believed to be connected to 

Natura 2000 site 2km away. 

Extension of existing Underpass which was being 

used by Lesser Horseshoe Bats, during the construction 

period. Extended culvert 2.4m by 2.4m, 

with existing culvert total length 67m. 

Construction of extension phased to be carried out 

during winter seasons when bats not flying and 

when other flight paths under the road were not being 

altered. 

Plastic guide fencing applied to ensure that bats 

were able to find the underpass. 

Work period between 2006 and 2008. 

(see also Case study 3) 

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Photograph: underpass 

during construction. Jacobs 

Decision made to remove traffic from underpass and to 

keep it purely for bats due to numbers of bats using the 

underpass and closeness of the underpass to the 

roost. Also a new route for traffic had been provided. 

There was a risk that work to extend the underpass 

during construction could stop or reduce the use of the 

underpass by the bats. 

Ongoing. Monitoring (2006 onwards) carried out on the 

basis of being similar to original baseline surveys 

(2004/5). Bats continued to use the underpass broadly 

as before. Occasionally small alterations to numbers of 

bats using the underpass occurred which are probably 

not related to works being carried out. See also Case 

Study 3. 

Case Study 3: A465 Heads of Valley Stage 1 Abergavenny to Hirwaun 


Context of the 

project 


Description of 

measure undertaken 

Wildlife Vehicle Collisions (operation); and health and safety 

of humans. 

Widening of existing road from 2 lanes (single carriageway) to 4 

lanes (dual carriageway). Open to traffic throughout construction 

period. 

Maternity roost of c90 individual bats within 300m of project. Bats 

regularly used the Underpass at Hopyard – c 120 - 500 individual 

movements recorded over one night. Roost believed to be connected 

to Natura 2000 site 2km away. 

Installation of grilles in Hopyard Underpass to stop humans 

accessing the underpass, other than for maintenance. 

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Photograph: 

New grille with 

bar removed. 

TACP 

To limit human access to tunnel to prevent damage occurring, 

while allowing bats through. Original proposal for metal angled 

grille at entrances of underpass made the bats to turn away and a 

small number to fly over the road at low level. Tests of types of 

grilles and location for the grilles within the tunnel carried out, by 

placing wooden frames at various distances from either end. 

Vandalism of frames forced decision to put final metal (type of 

metal) grilles at c1m from the tunnel entrances in 2009. 

Final grille dimensions: 

Bars 25mm diameter; vertical spacing between bars at top of 

grille 1.2 m; and horizontal spacing between supports 130mm. 

Ongoing. With the final grille and full set of bars in place, majority 

of bats turned away and went out of the tunnel. When one bar of 

the grille removed (see photo) bats passed through. Experiment 

in 2010 to see if bats will get used to full set of bars. 

Case Study 4: A477 Sageston to Redberth Improvement 


Context of the 

project 

Context for 

bats 

Damage to flight lines between roosting/feeding areas (construction) 

and Wildlife Vehicle Collisions (operation). 

New single carriageway to remove traffic from two villages. 

Road crosses flight routes to and from roosts and feeding areas. 

Numbers using routes relatively low at 2 individuals, but routes also 

used by up to 4 individuals of rarer Greater Horseshoe bats (Rhinolophus 

ferrumequinum). 

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2m diameter 

underpass in 

2006. Hyder 

Installation of “Armco” culverts during construction in 2001 – 

2.2m and 2m in diameter on exact flight paths, and 1 to 2m 

above ground level. Culvert size chosen as maximum size 

possible which could be installed. Embankment excavated to 

form entrance and shrubs planted to link into surrounding 

countryside. 

Risk of bat casualties became apparent when construction period 

surveys highlighted more use of flight lines than originally thought. 

Flight lines in culvert locations were across a new embankment, 

one culvert at an angle to the line of the road. 

Monitoring period 2001 – 2003. Majority of bats used underpasses 

almost immediately; one still flew over road. No road casualties 

recorded during survey periods. Please note small number of bats 

involved. 

Case Study 5: A479 Talgarth Relief Road 




Damage to flight lines between roosting/feeding areas 

(construction) and Wildlife Vehicle Collisions (operation). 

Single carriageway bypass and improvement of existing road to 

remove traffic from centre of town. At location of bat crossing - 

single carriageway and extra lane uphill. 

Maternity roosts found in old hospital and farms around the 

town, main flight path connecting roosts discovered to be “circu- 

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Existing culvert. 

Hyder. 

lar” around town using woods, hedgerows and large trees; and 

a river. New road crosses flight path where 10 to 17 bat movements 

using a flight path either along stream through existing 

culvert or across crowns of mature trees. 

Provision of new culvert (dimensions 2.5m) 15m from existing 

culvert (dimensions 0.9m). New culvert built outside of 

bat flight period winter 2006/7 and kept open during bats 

flight periods 2007. 

Need to maintain flight path after removal of hedgerow with mature 

trees. (See also Case study 6). Existing underpass also 

used by otters (Lutra lutra), badgers (Meles meles). 

Monitoring ongoing since 2006. At first bats split between flying 

through culverts and also through trees. Removal of branch 

from tree nearest road in winter 2007/8 moved all bats to use 

culverts. Results during and post construction (so far) suggest 

pathway remained in use in similar frequency and numbers as 

before. 

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Case Study 6: A479 Talgarth Relief Road 





undertaken 



Photograph: Temporary 

fencing in place. Hyder. 


(construction) 

Single carriageway bypass and improvement of existing road 

to remove traffic from centre of town. At location of bat crossing 

- single carriageway and extra lane uphill. 

Maternity roosts found in old hospital and farms around the 

town, main flight path connecting roosts discovered to be “circular” 

around town using woods, hedgerows and large trees; 

and a river. New road crosses flight path where 10 to 17 bat 

movements using a flight path either along stream through 

existing culvert or across crowns of mature trees. 

Temporary Construction Fencing*. Plastic fencing on 

metal frames moved away from the site during the day 

and returned to position at night during the bats flight 

period. Fencing along 40m gap between new culvert and 

the vegetation left in place. 

Risk that bats will not use flight route as no vegetation to follow 

or to offer protection from predators (eg: birds of prey, 

owls etc). 

Monitoring in 2006/7 showed that bats continued to use route 

with a similar frequency as before construction. 

* it should be noted that some UK advisors do not agree with providing temporary construction 

fencing. Consideration needs to be given to individual circumstances. 

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Case Study 7: A487 Llanwnda to South of Llanllynfi Improvement 





undertaken 





(operation). 

Single Carriageway provided to bypass three villages. 

Main roost 2.1km away is a Natura 2000 site. Surveys 

during construction (2001) found more bat activity than 

expected in a number of locations across the road. Radiotracking 

(2002/2003) confirmed that bats travelling 

across road using hedgerows/trees to feeding areas, 

and roosting and hibernacula sites. 

Bollard/Vertical road side lighting*. Type: Holophane 

Denver 18W to 24W compact fluorescence. 

Temporary lighting trialled in 2002, final installation 

2003. Planting and fencing also put in at bottom of 

embankment along a diverted stream to guide bats 

to the alternative crossing point. Planting was already 

on the embankment when the lights were installed. 

Construction surveys in 2001 found new embankment 

had been located on a flight line for 20 to 84 bat 

movements, rather than the 2 movements recorded 

previously. 6 lesser horseshoe bat casualties found 

within first year as bats were following the shape of 

embankment. 

Surveys ongoing since 2001. Numbers of movements 

at crossing point reduced to zero by end of 2003; with 

increase in activity at nearby bridge (Bethesda Bach 

Bridge) and in flight lines further away from crossing 

point (see Case Study 9). In 2007 major vandalism of 

the bollards created dark corridor, occasional surveys 

showed that bats did not return to the light. Casualty 

surveys carried out on a daily basis between mid- 

August and end of October/November each year (except 

2006) shown no further casualties at the original 

crossing point. 

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Photograph: Bollard light 

during the day. 2005. L 

Wyatt 

* Our approach is to use lighting as a last resort, after considering other options. Concerns 

have been raised that diverting flight lines of bats too far, may have impact on energy requirements 

of bats, although evidence to support or reject this is not available at present. 

Case Study 8: A487 Llanwnda to South of Llanllyfni Improvement 





undertaken 



(operation). 


Main roost 2.1km away is a Natura 2000 site. Surveys 

during construction (2001) found more bat activity than 

expected in a number of locations across the road. Radiotracking 

(2002/2003) confirmed that bats travelling 

across road using hedgerows/trees to feeding areas, 


Fencing at 2m and 4m height. 2m height with single 

and double extensions to stop bats crossing the 

road. Installed 2001/2. 

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Photograph: 2m high fencing 

with extensions. L Wyatt 

Around 1 to 8 movements per survey event had been 

made of bats continuing use 2 flight paths even though 

a new culvert (2m diameter) and new vegetation had 

been put into place. Approximately 1 to 2 casualties 

each year during 2001/2 in two locations. 

Did not work. 

Bats adjusted flight to return to ground level after flying 

up, around and over fencing. Number of movements of 

bats in the area remain similar to the original situation 

(1 to 8 movements), with occasional casualties (1 to 3 

in various years since). Difficult (if not impossible) to 

install any further mitigation at these locations, other 

than reinforcing and managing planting to guide bats to 

new culvert. 

Case Study 9: A487 Llanwnda to South of Llanllyfni Improvement 




Wildlife Vehicle Collisions (operation). 


Main roost 2.1km away is a Natura 2000 site. Surveys during 

construction (2001) found more bat activity than expected 

in a number of locations across the road. Radiotracking 

(2002/2003) confirmed that bats travelling across 

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undertaken 




road using hedgerows/trees to feeding areas, and roosting 

and hibernacula sites. 

“Ski Jump” consisting of an earth bank and large 

trees provided within grass area on one side of the 

road. (2004). See also Case Study 10. 

Up to 39 movements at this point each year since construction 

with only one casualty in 2003 so far. However, 

casualties at other nearby locations with fewer movements 

and consideration of the existing vegetation pattern at this 

location (see photograph), suggested that this point could 

be managed to become the preferred crossing point in the 

longer term. 

Monitoring since 2001 shows that number of movements 

at this location has dropped to between 2 and 12, possibly 

due to wet summers in 2007/8/9. Casualties limited at this 

location, but still occur at other locations nearby. Bats 

found to use ski jump then drop down to fly at ground level 

– see also Case Study 10. 

View from gap in hedge 

towards Ski Jump and 

across road 

L Wyatt 

Case Study 10: A487 Llanwnda to South of Llanllynfi Improvement 


Context of 

Damage to flight lines between roosting/feeding areas (construction) 

and Wildlife Vehicle Collisions (operation). 

Single Carriageway to bypass three villages 

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the project 

Context for 

bats 

Description 

of measure 

undertaken 


Results of 

monitoring 

Main roost 2.1km away is a Natura 2000 site. Surveys during construction 

(2001) found more bat activity than expected in a number of 

locations across the site. Radiotracking (2002/2003) confirmed that 

bats travelling across road using hedgerows/trees to feeding areas, 


T shaped bat bridge. Clearance from road 5.7m. Dimensions of T 

shape 2m by 2m. Wire mesh size 50mm x 50mm. T shape and 

detailed design chosen on advice of bat and bridge specialist 

advice. Installed January 2010. 

Up to 39 individuals each year crossing at this point. “Ski jump” (Case 

study 9) not sufficient to make bats fly over top of traffic. Existing 

vegetation on both sides of the road suggested link could be restored. 

None so far. Started in April 2010. 


Bat Bridge, 

Jan 2010, 

G Billington 

Case Study 11: A487 Porthmadog to Tremadog Improvement 




(construction) and Wildlife Vehicle Collisions (operation). 

Provides bypass of town and two surrounding villages at 

single carriageway standard. Sensitive landscapes and 

international and national sites throughout the area. 

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undertaken 



Bypass within 75m of roost of c420 individuals. 

Vegetated bridge, with fencing and planting to funnel 

bats, on exact line of existing flight path. Indicative 

design of the bridge requires it to be 7m wide and 

40m long with 1.8m high solid parapets (sides) to 

provide a dark corridor. Large planting boxes and upturned 

tree stumps, soil and branches from vegetation 

clearances will be laid out across the bridge. 

Detailed field survey (2004 to 2009) and radiotracking of 

females and juveniles (2005) had confirmed importance 

of movements from the roost across road at 5 locations. 

Most flight paths will have >2.5m underpasses for the 

bats to fly through aligned on the original flight paths. 

However, this flight path is over a cutting/valley. Considering 

the importance of the flight path (c 100 movements 

per night) the decision was made to provide it for bats 

only, although attempts were made to find another suitable 

non-bat use for the bridge which would have made 

the reasons for the bridge stronger. 

Construction has recently started. Construction monitoring 

due to start soon. 

Photograph: Design of 

proposed bridge. Halcrow. 

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4 SURVEYING CONSIDERATIONS 

Our published advice (Highways Agency et al, 2008, Nature Conservation Advice in relation 

to Bats) which covers all bat species, states that surveys should provide sufficient information 

to find out: 

• Which bat species are present 

• Where they roost and forage at different times of the year 

• What routes they use to travel between roosts and foraging areas within the 

immediate vicinity of the road/structure/tree/building concerned; and 

• How the project will impact on the bats and what mitigation can be included to 

reduce the significant effects. 

Critical to this is the scoping of the surveys (setting out and agreeing the details of the locations, 

timing and methodologies to be used to carry out the surveys); and also having the 

ability to review the scope of surveys during the survey period, in case changes need to be 

made. 

Generally, surveys will consist of reviews of existing information and field based surveys. 

For lesser horseshoe bats on our large scale projects with significant effects on flight lines, 

we do recommend that a full season’s surveys of flight lines (eg: from late April/May to September) 

are carried out. 

The intensity of those surveys over the season depends on the potential significance of effects 

of the project; and on the technology used. When using hand held bat detectors consideration 

should be made of surveying on two consecutive nights each month over the season. 

When automated detectors are used, this may be reduced, but consideration has to be given 

to the location and characteristics of the recorders. Special consideration is usually given in 

these surveys to recording how the bats fly across the road (eg: height and location). 

In some cases where projects have been delayed, we have kept the survey information up to 

date with ongoing surveys, as it is possible that overtime the use of the area by lesser horseshoe 

bats, or the population of the bats in the area changes. This is done so that any significant, 

and potentially long term changes can be identified early (eg: changes in flight lines, 

use of areas, or even failure of maternity roosts/hibernacula) and dealt within the design and 

assessment process. 

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5 DESIGN CONSIDERATIONS 

The aim of all of our design advice is to encourage a holistic and integrated approach to the 

way environmental issues are dealt with within the design and assessment processes we 

use. Examples of this would be the consideration of the design of a bat bridge within a sensitive 

landscape area; or the design of a road drainage scheme and its effects on bat flight 

paths and feeding areas. 

Experience has taught us that we need to ensure that: 

• Relevant designs are brought forward which are cost effective, and meet the 

requirements of legislation and guidance 

• There is close cooperation between engineers, ecologist and bat specialist as 

a good understanding of the actual situation and implications of mitigation is 

critical for those working on solutions. 

• That liaison with relevant organisations with responsibility for bats is carried 

out. 

• Understanding the context of the project and the bats is an extremely important 

consideration. 

6 MONITORING CONSIDERATIONS 

Our guidance states that monitoring is: 

• Vital to provide data on the success or failure of measures 

• Vital to increase our understanding of the use of roads by bats; 

And that it should be: 

• Appropriate to the mitigation provided 

• Agreed with the relevant parties 

I would add that monitoring should be included in the contract requirements to ensure that it 

is taken forward. 

For most of the projects here, there have been surveys to inform a baseline before the 

scheme is started (either during the design process or just before construction), which then 

informs the monitoring carried out during and after construction in terms of locations and survey 

effort. Bat casualty monitoring after construction have been usually considered on a case 

by case basis, depending on a judgement of whether there is a high risk of failure of mitigation 

measures causing road casualties. 

From experience we have found that it can be difficult to isolate the effects or changes potentially 

caused by the road on movements and populations, and those caused by non-road 

21







sources (eg: bad weather, changes in sizes of roosts, physical changes to the roost itself, or 

where a large roosts split into two). 

7 CONCLUSIONS 

The paper has described the context in which the Welsh Assembly Government undertakes 

its work with Lesser Horseshoe Bats and large new road projects. 

It is true to say that our knowledge since the beginning of the century has improved, and we 

are now able to refer to examples of successful mitigation to support the application of mitigation 

in new circumstances after considering the context involved. However, some measures 

which have been applied have had to be based on best professional judgement of the 

situation involved, and only monitoring will tell whether they are effective. 

We are hoping to: 

• Continue to learn from our experiences, and the experience of others in similar 

situations. 

• Continue to improve the ability of engineers, ecologist and bat specialists to 

understand the issues involved, and develop practical solutions to avoid, reduce 

or if possible remedy effects. 

• Improve the way we understand context of the projects and the use of the surrounding 

areas by bats 

• Improve the way we undertake Environmental Impact Assessment and “Appropriate 

Assessment”/Assessment of the Implications on European Sites. 

8 FURTHER UK BASED INFORMATION 

Please note that not all of the references are specifically written for the road situation. Those 

that are have a * next to them. 

Bat Conservation Trust, 2007, Bat Surveys Good Practice Guidelines, Bat Conservation 

Trust. 

*Bickmore, C, 2003, Review of work carried out on trunk road network in Wales for bats, 

Welsh Assembly Government and Countryside Council for Wales – from 

or author 

Entwhistle, A et al, 2001, Habitat Management for Bats – A guide for land managers, land 

owners and their advisors, JNCC, 

*Highways Agency et al, 2008, Design Manual for Roads and Bridges – Interim Advice Note 

– Nature Conservation Advice in relation to Bats 116/08 

English version – 

22







Wales version – 

or from Author 

Mitchell – Jones AJ, 2004, Bat Workers Manual (3 rd Edition), JNCC 

Schofield, H, 2009, Lesser Horseshoe Bat Conservation Handbook, The Vincent Wildlife 

Trust 

Other UK National Highway Authority contacts: 

• England - Stuart Wilson, Highways Agency – 

• Northern Ireland – Stephen Tweed , Roads Service – 

 

• Scotland – Angus Corby, Transport Wales – 

 

9 ACKNOWLEDGEMENTS 

1 Contractors and Consultants for case study information and photographs: 

Mowlems/TACP/Gwynedd Council/Greena Ecology – A487 Llanwnda to South of Llanllynfi 

Improvement 

BAM Nuttall/TACP/Jacobs – A465 Heads of Valley Dualling Section 1 

Jacobs – A465 Heads of Valley Dualling Section 2 

Halcrow/WYG – A487 Porthmadog to Tremadog Improvement 

BAM Nuttall/Hyder/WYG/Just Mammals – A479 Talgarth Relief Road 

BAM Nuttall/Arup/Hyder/Cresswell Associates – A477 Sageston to Redberth Bypass 

2 For comments on the paper: 

Stuart Wilson, Highways Agency 

Jean Matthews, Countryside Council for Wales 

23







3 Finally, I would like to thank to all the Welsh bat groups, and individual engineers and bat 

workers who while not mentioned above, have assisted with increasing our understanding of 

the issues we are facing and developing solutions. 

Len Wyatt CEnv MIEEM 

Environment Science Advisor, 

Transport and Strategic Regeneration, 

Telephone: 044 (0)2920 82 6780 

Email: len.wyatt@wales.gsi.gov.uk 

Welsh Assembly Government, 

Cathays Park 

Cardiff, Wales, UK, CF10 3NQ 

 

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