Bat survey report for Claude Smith's Collyweston Slate Mine, Slate Drift Industrial Estate, Collyweston, Northamptonshire, PE9 3PG Oakwood Ecology

by Simon Cope MSc MCIEEM

For: Nigel Smith Claude N. Smith Slate Drift Industrial Estate Collyweston Northamptonshire PE9 3PG

November 2014 (revision #4.1, August 2015)

Oakwood Ecology Pen-y-geulan, Cefn Coch, Llanrhaeadr-ym-Mochnant, Powys, SY10 0BT. Tel. 01691 780783 Mob: 07772 768461 eMail: [email protected] For Nigel Smith Claude Smith's Mine bat survey report (Revision #4.1)

Contents

Summary ...... 3

1 Introduction...... 4

1.1 Overview ...... 4

1.2 Proposed works ...... 4

1.3 Aims of study ...... 5

1.4 Authors qualifications ...... 5

2 Legislation and policy guidance ...... 7

2.1 Legislation overview ...... 7

2.2 Licensing ...... 7

3 Methodology ...... 8

3.1 Desk study ...... 8

3.2 Field survey ...... 9

4 Results ...... 11

4.1 Desk study ...... 11 Designated sites ...... 11 Historical records ...... 11 Northamptonshire ...... 11 Leicestershire and Rutland ...... 12 Lincolnshire ...... 12 Cambridgeshire ...... 13 Current availability of other hibernation sites ...... 13 4.2 Preliminary field survey ...... 16 Habitat description ...... 16 Preliminary site inspection ...... 17 4.3 Bat surveys ...... 18 Claude Smith’s Mine...... 18 Osborne’s Mine ...... 21

5 Assessment ...... 24

5.1 Constraints ...... 24 Survey information ...... 24 Equipment used ...... 24 5.2 Current Value of the site ...... 24

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Designated sites ...... 24 Bat roosts ...... 24 Foraging and commuting habitat ...... 26 5.3 Impact assessment ...... 26

6 Recommendations and mitigation ...... 28

6.1 Further survey work...... 28

6.2 Mitigation measures ...... 28 Mitigation for bat roosts ...... 28 Phase 1 ...... 29 Phase 2 ...... 30 Post-mining restoration ...... 30 Supervision by the Ecological Clerk of Works ...... 30 Mitigation for swarming activity ...... 34 Mitigation for foraging and commuting habitat ...... 35 Enhancement for commuting and foraging habitat ...... 35 Post-commencement monitoring ...... 35 Predicted impacts after the implementation of the mitigation measures ...... 38 Requirement for Habitats Regulations (EPS) licences ...... 38

7 References ...... 40

Appendix 1 Historical records (see PDF’s) ...... 41

Appendix 2 Photographs ...... 42

Appendix 3 Raw survey data ...... 48

Appendix 4 Sample sonograms ...... 56

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Summary

This report presents an assessment of the activity of bats at Claude Smith’s Collyweston Slate Mine, Slate Drift Industrial Estate, Collyweston, Northamptonshire, PE9 3PG (Grid ref. TF00050330), where it is proposed to re-open the old mine for the extraction of 'Collyweston Slate'. It includes the results of a desk-study, an assessment of the surrounding habitats and the results of a series of surveys. Industry-standard survey methodologies were followed.

There are 11 statutorily designated sites within 5km of the proposed development site, none of which are notified because of bats. The desk study yielded 302 historical records of bat activity within 5km of the site and at least 18 hibernacula within 20km, including data on 11 different species.

A range of field surveys were carried out in and around the mine, including a survey of the habitats surrounding the mine, two underground surveys to check for hibernating bats and three activity surveys to investigate how bats were using the mine through the year. Similar field surveys were carried out at a similar mine just to the north (Osborne's Mine) to put these results in context.

A total of seven species were recorded during the surveys, three of which were observed roosting in Claude Smith's Mine. A maximum of seven individuals were observed hibernating in the mine, and baseline data on the temperature and humidity regime in the mine has also been collected. 26 individuals were observed to enter or emerge from the mine during the activity surveys.

The mine is considered to be of local value as a hibernation and swarming site and for day roosting purposes. Re-opening the mine could impact upon the resident bat populations in a number of ways, including the potential for inadvertent exclusion, physical harm and disturbance, so a phased extraction plan is proposed which will ensure that the bats are kept separate from mining activities at all times. If the mitigation measures outlined in this report are followed in full, bats can continue to use parts of the mine throughout the operational phase and into the future, and both the underground and above-ground habitats will be significantly enhanced. A site-specific EPS licence will be required, and further bat surveys are proposed in order to monitor the population of bats both after mining has commenced and after all extraction has been completed.

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1 Introduction

1.1 Overview

1.1.1 This report presents an assessment of the activity of bats at Claude Smith’s Collyweston Slate Mine, Slate Drift Industrial Estate, Collyweston, Northamptonshire, PE9 3PG (Grid ref. TF00050330, Figure 1), carried out to inform a planning application in accordance with instructions from Mr Nigel Smith.

Figure 1. Location map of Slate Drift Industrial Estate at Collyweston.

1.1.2 The development proposes to re-open the old mine for the extraction of 'Collyweston Slate', which is in fact a fine-grained, sand-rich limestone, that has been used as a roofing material on many local heritage buildings as well as on notable historic buildings further afield. A large proportion of these buildings are either Listed by English Heritage or are in Conservation Areas, where planning consent hinges on using the same materials when re-roofing (English Heritage, 2005). No virgin material has been commercially extracted for some decades and the supply of slate suitable for reclamation has dwindled. The re-opening of this mine is an attempt to address this supply problem, and it is in full accordance with Policy 6 of the Northamptonshire County Council Mineral and Waste Local Plan (NCC, 2014).

1.2 Proposed works

1.2.1 The existing site layout is shown below (Figure 2). Due to the small scale of the mine workings, there will be very little change to the above-ground use of the site. The

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western end of the site, that has been used to stockpile reclaimed slates in the past, will be used for storage of the slate 'logs' while they undergo the necessary weathering period (approximately three winters) that has traditionally been used to bring them into a usable state. In order to comply with mine safety regulations, a second entrance will be required. This will also be located within the industrial estate boundary and can be used to bring the logs to the surface.

Old shaft

Figure 2. Existing site layout at Slate Drift Industrial Estate, showing location of mine old shaft and mine passages (outlined in red) in relation to surface features.

1.3 Aims of study

1.3.1 The aims of the surveys were:

 To establish the presence or likely absence of bats (Order Chiroptera) on the site, and;

 If they are found to be present, to carry out further survey work to determine the types of use, so that a suitable management strategy can be implemented, i.e., mitigation and/or compensation measures.

1.4 Authors qualifications

1.4.1 My formal qualifications include an MSc in Biological Recording from Birmingham University. I have attended many relevant short courses including standard and

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advanced bat survey techniques, difficult sonogram analysis, ecological impact assessment and mitigation.

1.4.2 I am an active member of the Shropshire Bat Group and Chairman of the Montgomeryshire Bat Group; I am licensed to survey bats in England (Licence no. CLS01741 and Class Licence Level 4 registration no. 2014-5549-CLS-CLS) and Wales; I have been carrying out mine surveys for bats since 2010; and I have been a self- employed Ecological Consultant since 2004, having worked with a wide range of habitats and species.

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2 Legislation and policy guidance

2.1 Legislation overview

2.1.1 All British bat species are protected by statutory law. Historically, national laws such as the WCA and the CRoW Act (2000) have provided partial protection, but the most wide-ranging and comprehensive legislation now stems from European legislation, which, in England and Wales, is enacted by the Conservation of Habitats and Species Regulations 2010.

2.1.2 Under these regulations, it is an offence to: deliberately capture, injure, kill or disturb any bat; damage or destroy a breeding site or resting place of a bat; be in possession of, or to control, transport, sell or exchange or to offer for sale or exchange any bat (living or dead) or part of a bat. With regard to bats, the term ‘disturb’ includes any roost, whether occupied or not, where the disturbance will a) impair their ability to survive, reproduce or rear their young, or to hibernate, and b) affect significantly the local distribution or abundance of that species.

2.2 Licensing

2.2.1 In order to carry out work which may affect any European Protected Species (EPS) in the ways outlined above, an EPS License is required. For an ecological surveyor in England, this means a Level 2 Bat Survey class licence (WML-CL18). For a particular development a project-specific derogation must be granted in the form of a development licence from Natural England (NE).

2.2.2 In order to qualify for a development licence, the development must meet the ‘three tests’:

 It must preserve public health or public safety or satisfy other imperative reasons of overriding public interest including those of a social or economic nature and beneficial consequences of primary importance for the environment (Reg. 53 (2) (e));  There is no satisfactory alternative (Reg. 53 (9) (a)), and;

 The action authorised will not be detrimental to the maintenance of the species concerned at a favourable conservation status in their natural range (Reg. 53 (9) (b).

2.2.4 With regards to the Local Authority policy, the presence of a protected species is a ‘material consideration’ in the planning process. It is, therefore, essential that the presence or otherwise of a protected species, the extent to which they will be affected by the development, and any mitigation and compensation measures are established before planning permission is granted (National Planning Policy Framework, 2012).

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3 Methodology

3.1 Desk study

3.1.1 The site is located in the north of Northamptonshire, in close proximity to four different Local Records Centres (Figure 3). Bats are highly mobile, so records of all bat activity within 5km of the site were requested. Due to the temperature and humidity regime prevalent in underground sites, they are particularly useful to bats as hibernacula. A shortage of suitable sites might mean that this site is particularly valuable in a regional context, so records of all hibernacula and hibernating bats within 20km were also requested.

3.1.2 The following sources were consulted:

 The Local Biological records centre(s) or other bodies responsible for the curation of bat records, i.e., Northamptonshire Bat Group, Cambridgeshire Bat Group, Greater Lincolnshire Nature Partnership and Leicestershire and Rutland Environmental Records Centre;  The National Biodiversity Network (NBN) Gateway (www.nbn.org.uk);

 The National and Local Biodiversity Action Plans (www.ukbap-reporting.org.uk);  MAGIC interactive maps (www.magic.gov.uk)

Figure 3. Disposition of Local Biological Records Centres consulted, also showing the 5km search radius for all records of bat activity and the 20km search radius for bat hibernacula records (map provided by Lincolnshire Environmental Records Centre).

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3.2 Field survey

3.2.1 All landscape-scale habitat features in the immediate vicinity that may be used by bats are identified, including any habitats suitable for foraging, commuting or roosting.

3.2.2 The mine inspection and dusk/dawn activity survey methodologies followed the guidelines published in Mitchell-Jones & McLeish (2004) and Hundt (2012).

3.2.3 The initial mine survey involved a search to check for bats and the field signs that they produce, and an assessment of the habitats in the immediate vicinity to assess their suitability for commuting and foraging bats. In order to put the findings at Claude Smith’s Mine in context, surveys were also carried out at the nearby Osborne’s Mine - another small ‘slate’ mine thought to be of a similar age.

3.2.4 Field signs can include: live bats present, bat corpses, droppings, feeding remains, oil and/or urine staining, or a distinctive smell, all of which, by virtue of their location or other characteristics, can be species-specific. The presence of suitable holes and crevices is also noted, although, by themselves, these are not evidence of occupation.

3.2.5 Various items of specialist equipment are used to aid the mine surveys, including: ladders, powerful torches, an endoscope and mirrors for looking into crevices and inaccessible nooks and crannies.

3.2.6 The surveys were designed to ascertain the species and number of bats using the site throughout the year. In broad terms, the winter surveys were timed to detect hibernating bats, the April activity survey would detect bats using the mine as a transitional roost in the Spring, the July survey would pick up any activity associated with a significant maternity roost (along with any solitary males or non-breeding females), and the October survey was designed to detect ‘swarming’ activity, where bats congregate to mate and to investigate potential hibernation sites.

3.2.7 A suitable number of surveyors were used to provide effective coverage; in this case one surveyor per mine entrance, each able to view the whole entrance. A bat detector was also left inside the mine to passively record bat activity over a longer period in the winter (22 days), and data-loggers were stationed at the ends of the north and south passages to record the temperature and humidity over the same period.

3.2.8 Specialist equipment used during these surveys includes: Anabat SD2 bat detectors (with real-time sonogram display), Elekon Batscanner heterodyne bat detectors, Yukon 1×24 Night Vision Goggles with infra-red torches, a Yukon Exelon 3 × 50 night vision scope, and a set of Binatone Walkie-Talkies to assist in tracking bats between surveyors.

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3.2.9 All of the Anabat bat detectors are capable of recording sonograms, and these were analysed using specialist computer software (AnalookW) to identify individuals to species level where possible. Some of the bat species found in the UK can have significantly different requirements, so this determination may be important when considering appropriate mitigation measures.

3.2.10 Different bat species produce sonograms of varying distinctiveness, and the sonograms recorded on these surveys have been identified using the criteria given in Russ (2012), Middleton et al. (2014) and from information imparted on training courses (S. Sowler, G. Billington, M. Worsfold pers. comm’s.).

3.2.11 The calls of some species, e.g., Pipistrelles, are usually relatively straightforward to identify from a sonogram. The different Myotis species can be difficult to distinguish even when a high quality sonogram is recorded because they are so similar. Natterer’s and Daubenton’s Bats have been identified with a reasonably high degree of confidence (~80%), whereas Whiskered and Brandt’s Bats are often less easy to separate (approx. 60% confidence, i.e., the bat is slightly more likely to be a Whiskered than a Brandt’s).

3.2.12 Reliable information on the calls of Alcathoe Bats (Myotis alcathoe) is not available, and the calls of Bechstein's Bats are indistinguishable from other Myotids. There are no historical records of either of these species in this region, and they have therefore been discounted from the analysis.

3.2.13 The frequency of calls are categorised on a subjective scale ranging from Constant, through Frequent, Occasional to Rare. Continuous calls do not necessarily indicate a steady stream of bats because all of the calls may be emanating from one bat repeatedly passing within range.

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4 Results

4.1 Desk study

Designated sites

4.1.1 There are 11 statutorily designated sites within the 5km search radius (Table 1), none of which are notified because of bats.

Approximate Site name Designation distance Reason for designation from site Collyweston Slate Mine (aka SSSI 225m Geology Spall’s Mine) Geology and Collyweston Quarries SSSI 500m invertebrate fauna Racecourse Farm Fields SSSI 1.7km Geology and botany Collyweston Great Wood and NNR and 1.7km Botany Eastern Hornstocks SSSI Ketton Quarries SSSI 2.8km Geology and botany Bonemills Hollow SSSI 3.6km Botany Botany and invertebrate Luffenham Heath Golf Course SSSI 3.8km fauna North Luffenham Quarry SSSI 3.9km Botany Whitewater Valley SSSI 4.0km Botany NNR and Bedford Purlieus 4.6km Botany SSSI Shacklewell Hollow SSSI 4.9km Botany

Table 1. Designated sites within the 5km search radius.

Historical records

4.1.2 Below is a summary of the information received from each of the four Local Records Centres and Bat Groups. The detailed results are not included in this report because some are classed as confidential by the bodies who supply them. The records can be supplied given the prior agreement of the providers. Figures 4 & 5 show the distribution and history of the hibernacula recorded within 5km and 20km of the site.

Northamptonshire

4.1.3 There are no historical records from Claude Smith's Mine. A total of 51 records have been recorded within the 5km search radius, including seven species: Common and Soprano Pipistrelle (Pipistrellus pipistrellus and P. pygmaeus) (and undifferentiated Pipistrelles), Brown Long-eared Bat (Plecotus auritus), Daubenton's Bat (Myotis daubentonii), Natterer's Bat (M. nattereri), Whiskered Bat (M. mystacinus), Brandt's

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Bat (M. brandtii) (and undifferentiated Whiskered/Brandt's Bats), Noctule (Nyctalus noctula) and Barbastelle (Barbastella barbastellus).

4.1.4 Of these, 18 were records of hibernating bats. Of particular relevance are the counts carried out by the Cambridgeshire Bat Group at the nearby Osborne's Mine (150m to the north) and Spall's Mine (280m to the south-south-west, designated as Collyweston Slate Mine SSSI), where a maximum of 28 and 29 hibernating bats have been counted respectively (as recently as 2005 in the case of Osborne's Mine).

4.1.5 The nearest record of a Barbastelle, which receives additional legal protection under Annex 2 of the Habitats Directive 1992 (as amended), is of an individual foraging in the woodland at Bedford Purlieus, over four kilometres away in 2007.

4.1.6 Hibernating bats have also been found in the mine on the Collyweston Slate Quarries SSSI which is managed by the Bedfordshire, Cambridgeshire and Northamptonshire Wildlife Trust (unspecified numbers of Brown Long-eared and Daubenton's Bats) and in the air raid shelters in Collyweston Great Wood (Brown Long-eared and Natterer's Bats) and in the Bedford Purlieus (e.g., 45 Brown Long-eared, 11 Natterer’s, and 2 Barbastelle in 2013).

Leicestershire and Rutland

4.1.7 In this catchment, there are 147 records within 5km of the site, including records of the following species: Barbastelle (6 sonogram records, all at the same location in 2011, approx. 3km away); Common Pipistrelle (15 records, 1 at a roost); Soprano Pipistrelle (18 records, 4 at roosts); Nathusius' Pipistrelle (Pipistrellus nathusii) (2 sonogram records at same location and year as the Barbastelle); undifferentiated Pipistrelle (18 records, 5 at roosts); Brown Long-eared (10 records, 7 at roosts); undifferentiated Long-eared Bat (5 records, 1 at a roost); Daubenton's Bat (8 records, 6 at a hibernaculum 4.1 km away); Natterer's Bat (7 records, 6 at the same hibernaculum); undifferentiated Myotid species (14 records, 5 at the same hibernaculum); Noctule (9 records), and; undifferentiated bats (28 records, 19 at roosts including 2 hibernating at the same hibernaculum as above).

4.1.8 There are 33 records of hibernating bats within the 20km search radius (including 11 outside the 5km radius). These include 21 of assorted species at the hibernaculum 4.1 km away, 3 of Barbastelle and a Natterer's Bat at a hibernaculum 8km away, and seven miscellaneous records (two of which are probably the same bat), the closest of which is approximately 2.4km away.

Lincolnshire

4.1.9 All 55 records returned by the Greater Lincolnshire Nature Partnership within the 5km search radius originate from the town of Stamford and include Common and Soprano Pipistrelle (and undifferentiated Pipistrelle species), Brown Long-eared Bat, Daubenton's Bat, an undifferentiated Myotid species, Noctule and undifferentiated bat species, the closest of which is approximately 4.5km away from the site.

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4.1.10 There are 73 records from one hibernaculum located approximately 17km away. This roost has been surveyed every year since 2001, and includes Barbastelle (a maximum of four individuals), Whiskered/Brandt's Bat (max. 1 bat), Natterer's Bat (max. 3 bats), undifferentiated Pipistrelle species (max. 15 bats) and Brown Long- eared Bat (max. 3 bats). The other three records of hibernacula are all for single bats (a Long-eared Bat at 4.7km, a Barbastelle at 14.1km and an undifferentiated Pipistrelle species at 16.9km).

Cambridgeshire

4.1.11 There are 49 records of bats within the search area from this county, including Common Pipistrelle (4 records), Soprano Pipistrelle (5 records), Brown Long-eared Bat (11 records, including 9 hibernation counts with a maximum of 5 individuals), Daubenton's Bat (4 records, all hibernation counts, max. 1 bat) , Natterer's Bat (7 records, all of hibernating bats, max. 3 bats), undifferentiated Myotid species (6 records, including 1 of 2 bats hibernating), Noctule (5 records), Serotine (Eptesicus serotinus) (5 records) and Barbastelle (2 records).

4.1.12 There are two main hibernacula that have been regularly surveyed within the 20km search radius: one at Bedford Purlieus (in various concrete bunkers between 5 and 6km away) and one in a cave 17.4km away from the site.

Current availability of other hibernation sites

4.1.13 Two of the eight hibernation sites within 5km are residential properties that have single records of solitary bats. Of the remaining six sites, Osborne’s Mine has been included in the surveys for this report and is known to be open and accessible to bats, and the roosts at the Collyweston Quarries Nature Reserve, Collyweston Great Wood air raid shelter, Bedford Purlieus and Ketton Gorse have all been confirmed as being open and available to bats (pers. comm’s, July, 2015). Indeed, the roosts at Collyweston Great Wood, Bedford Purlieus and Ketton Gorse are all actively managed by their owners for bats and regular monitoring is undertaken.

4.1.14 The ownership of Spall’s Mine has recently changed and it has not been possible to gain permission to inspect it. Its status as a roost is not known.

4.1.15 The only site where detailed records have been forthcoming is at Bedford Purlieus, where winter surveys in 2013 and 2014 recorded up to 45 Brown Long-eared Bats, 11 Natterer’s Bats and two Barbastelles (pers. comm. July, 2015).

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Unidentified roost Single Brown Long-eared recorded in 2011.

Ketton Gorse Collyweston Wildlife Trust A maximum of 9 Mine Daubenton’s, 9 Natterer’s, 5 Brown Long-eared, undientified Myotids and a Daubenton’s and Natterer’s single Brown Long-eared recorded 1993 and 1997. recorded between 1992 and 1999 Osborne’s Mine Brown Long-eared, Residential property Daubenton’s, Natterer’s, Single indeterminate Whiskered and Brandt’s Pipistrelle recorded in 2002 recorded from 1989.

Spall’s Mine Brown Long-eared, Daubenton’s, Natterer’s, Whiskered and Brandt’s recorded from 1988.

Collyweston Great Wood air-raid shelter Brown Long-eared, Daubenton’s and Natterer’s recorded from 2010.

Bedford Purlieus (unspecified location) Barbastelle recorded before 2007.

Figure 4. Historical information at each Bat hibernacula recorded within 5km of the site.

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Toft Tunnel Up to 4 Barbastelle, 3 Burley-on-the-Hill Natterer’s, 1 Single indeterminate Whiskered/Brandt’s, 3 Pipistrelle recorded in 1988. Brown Long-eared and 15 indeterminate Pipistrelle recorded between 2001 and 2012. Exton Single indeterminate Witham-on-the-Hill Pipistrelle recorded in 2005. Single Barbastelle recorded in 2003.

Deeping St James Single indeterminate Pipistrelle recorded in 1987. Oakham Road Single Brown Long-eared St John’s Close recorded in 2001 and 2012. Single indeterminate Pipistrelle recorded in 1990.

Morcott Single Barbastelle recorded Monk’s Cave in 2007, 2009 and 2010, and Up to 2 Natterer’s, 2 single Brown Long-eared Daubenton’s and 2 Brown recorded in 2001. Long-eared recorded between 2005 and 2012.

Bedford Purlieus (various air-raid shelters) Up to 2 Natterer’s and 14 Brown Long-eared recorded in 2006.

Figure 5. Historical information at each Bat hibernacula recorded within 20km of the site.

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4.2 Preliminary field survey

Habitat description

4.2.1 The preliminary site survey was carried out on the 15th of November, 2013, and representative photographs are presented in Appendix 2. Claude Smith's Mine is entered by a vertical shaft (approx. 8m deep) and horizontal passages extend from the base of this to the north and south (see Figure 2).

4.2.2 The habitats adjacent to the old shaft include a mixture of tarmac, concrete and bare earth, with a number of modern sheds, porta-cabins, caravans, palettes and piles of building materials. There is an overgrown hedge composed almost entirely of Hawthorn (Crataegus monogyna) with occasional gaps that forms the western boundary of the industrial estate. A hedge forming the eastern boundary is made up of densely-planted, occasionally-trimmed Beech (Fagus sylvatica).

4.2.3 In the west of the site, there is an area of scattered scrub with Buddleia (Buddleia davidii) and patchy tall ruderal weeds (e.g., Rosebay Willowherb (Chamerion angustifolium) and Nettle (Urtica dioica)) grown over the original hard-standing and scattered piles of building materials.

4.2.4 The habitats immediately surrounding the industrial estate include species-poor, semi-improved grassland, arable fields and domestic gardens (Figure 6). The entrance to Osborne’s Mine is at the base of a small quarry overgrown with mature trees approximately 150m to the north. The River Welland lies approximately 1km to the west.

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Collyweston Quarries Mine (not found) River Welland

Osborne's Mine

Claude Smith's Mine

Spall's Mine aka 'Collyweston Slate Mine SSSI'

Figure 6. Aerial photograph showing the habitats surrounding the site.

Preliminary site inspection

4.2.5 None of the buildings on the site offered any potential for roosting bats. Both Claude Smith's and Osborne's Mines offered many crevices for roosting bats, including cracks in the rock and gaps between stacked ‘deads’ (walls of waste rocks used to hold back spoil). The preliminary underground survey in Claude Smith’s Mine discovered two bats – one Whiskered/Brandt’s Bat (Myotis mystacinus/M. Brandtii) (it is not possible to differentiate these species without handling), and one Daubenton’s Bat (Myotis daubentonii), both in relatively deep torpor (see Figure 7). Scattered bat droppings were observed at a number of places in the mine. No bat- generated ultrasound was detected with the bat detector during this survey.

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Daubenton’s Bat

Whiskered/Brandt’s Bat clinging to roof

Old shaft

Figure 7. Plan of Claude Smith’s Mine showing the location of the bats found during the preliminary survey.

4.3 Bat surveys

Claude Smith’s Mine

4.3.1 A summary of the date, time, weather conditions and observations of the activity surveys are given in Tables 1, 2 and 3. The full list of sonograms recorded is presented in Appendix 3 and sample sonograms are presented in Appendix 4. The vantage point was chosen to provide effective coverage of the entrance to the mine, and the surveyors included Simon Cope (licence no. CLS01741) and Nicola Wheeler (CLS01740).

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4.3.2 Two surveys were carried out during the hibernation period in early 2014. No bats were found at Osborne’s Mine at this time, but the results of the surveys at Claude Smith’s Mine are presented in Table 2.

Winter Winter

survey #1 survey #2

Date 31/01/14 21/02/14

External temp. 5 9.8 (°C) External 78 28 humidity (%rh) Temp. at base of 7.1 8.8 old shaft Humidity at base 90 82 of old shaft Temp. at end of 9.9 10.1 north passage Humidity at end 83 91 of north passage Temp. at end of 8.8 10.1 south passage Humidity at end 94 91 of south passage <80cm deep, flooded through 90% Water level <15cm deep in discrete pools of mine Three indeterminate Myotids in a One Natterer’s Bat and 5 crack in the wall 2m from the base indeterminate Myotids in cracks in of the old shaft, one Daubenton’s the walls of old shaft, and one Bat amongst the stacked ‘deads’ in Natterer’s in a shot-hole near the Bats found the chamber just north of the north end of the north passage. entrance, and one Daubenton’s Bat clinging to the roof in the roof of the north passage.

Table 2. Results of the hibernation surveys at Claude Smith’s Mine.

4.3.3 Bats usually choose hibernation sites that maintain a very stable temperature and humidity regime. This is well illustrated by the information gathered by the data- loggers deployed in the mine for the period between the two winter surveys (Figures 8 & 9). These graphs also show that there is a negligible difference in temperature and humidity between the two ends of the mine.

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Celsius(°C) Humidity(%rh)

10 100 9 95 8 90 7 85 6 80 5 75

Temp.˚C 4 70 3 65 Humidity %rh 2 60 1 55 0 50

Figure 8. Graph showing temperature and humidity levels at the north end of the north passage between the two winter surveys.

Celsius(°C) Humidity(%rh)

12 110

10 100

8 90

6 80 Temp˚C

4 70 Humidity %rh

2 60

0 50

Figure 9. Graph showing temperature and humidity levels at the south end of the south passage between the two winter surveys.

4.3.4 The following species were heard and/or seen during the activity surveys at Claude Smith’s Mine: Common Pipistrelle (Pipistrellus pipistrellus; Ppip), Noctule (Nyctalus

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noctula; Nn), Natterer’s Bat (M. nattereri; Mn), and undifferentiated Myotid species (Myotis). See Tables 3, 4, & 5 for a summary of the results.

4.3.5 During the course of the activity surveys, a total of 26 bats were observed to roost in the mine. Three of these were observed emerging during Activity Survey #1 (in April), the remainder were recorded entering during Activity Survey #3 (October), although the latter may have entered the mine purely for social purposes and not to roost as such. No sonograms were recorded during Activity Survey #1, but all of the sonograms recorded during Activity Survey #3 were of either Natterer’s Bats or undifferentiated Myotis species. The amount of passes coupled with the behaviours observed during the October survey indicate swarming activity, where bats gather to socialise, mate and/or investigate hibernation sites.

4.3.6 During the October survey, bat activity detected from the vantage points of the surveyors was greater at Osborne’s Mine (Figure 10), although more bats were seen to enter Claude Smith’s Mine. This difference may be related to the topography around the respective entrances and it is assumed that the majority of the swarming behaviour at Claude Smith’s Mine was carried on underground.

4.3.7 No consistent flight-lines to or from the mine entrance were observed during the surveys.

Osborne’s Mine

4.3.8 No bats were recorded in Osborne’s Mine during the two winter surveys, although this does not mean that there were none hidden there – in both mines, there were many crevices that could not be examined fully. During the activity surveys, a wider variety of species were detected, including Common Pipistrelle, Daubenton’s Bat (Md), Natterer’s Bat, Whiskered Bat (Mmys), Brandt’s Bat (Mbr), undifferentiated Whiskered/Brandt’s Bat (MmysMbr) and undifferentiated Myotid species.

4.3.9 Two bats emerged from Osborne's Mine during Activity Survey #1. At one point during Activity Survey #3 at least six bats were observed in the mine, although the rapid chasing in and out of the entrance made an exact count difficult. As with Claude Smith’s Mine, the behaviours observed during the October survey could be described as swarming activity.

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Activity Survey #1: 17/04/14 Start: 19:49, Finish: 22:04 Weather: Dry, 2/3 cloud cover, Wind <11km/hr Temperature: 9.5 – 7.5 °C

Recorder Location Comments 1 quiet bat emerged at 21:09. 1 quiet bat entered crack in old shaft at 21:31. Claude 1 quiet bat emerged at 21:55. Nicola Wheeler Smith’s Quiet bats seen flying in old shaft between 21:01 Mine and 21:55. No sonograms recorded but picked up on heterodyne Batscanner = quiet Myotis. One Mmys emerged at 20:59. One Mmys emerged at 21:18. Osborne’s Common Pipistrelle foraging in quarry, constant Simon Cope Mine between 20:29 and 20:40. Mmys foraging in quarry, constant from 20:41 until end of survey.

Table 3. Summary of the results of Activity Survey #1 (a dusk survey in April).

Activity Survey #2: 04/07/14, Start: 02:45, Finish: 04:45 Weather: Dry, 2/3 cloud cover, Wind <2km/hr Temperature: 9.5 – 7.5 °C

Recorder Location Comments No bats roosting. One quiet bat entered and re-emerged from mine Claude shaft. Nicola Wheeler Smith’s Rare Ppip heard not seen (social calls) (03:01, Mine heterodyne only). Rare Noctule heard not seen (03:47, heterodyne only). No bats roosting. Ppip foraging and social calls around quarry, Osborne’s Simon Cope occasional – frequent from start until 03:51. Mine Md and undifferentiated Myotid frequent from start until 04:02.

Table 4. Summary of the results of Activity Survey #2 (a dawn survey in July).

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Activity Survey #3: 03/10/14, Start: 20:15, Finish: 22:35 Weather: Dry, 1/3 cloud cover, Wind <10km/hr Temperature: 18.6 – 13.8 °C

Recorder Location Comments 23 Natterer’s Bats or undifferentiated Myotids Claude entered the mine. Nicola Wheeler Smith’s Constant activity observed in old shaft, including Mine chasing behaviour. Frequent/constant activity of Mn, Md, Mmys, Mbr, Osborne’s MmysMbr and undifferentiated Myotis in the mine Simon Cope Mine and around the quarry from 20:31 until the end of the survey, including chasing and social calls.

Table 5. Summary of the results of Activity Survey #3 (a night survey in October).

25 Osborne's Claude Smith's

20

15

10 Numberofpasses

5

0

Figure 10. Graph showing bat activity (number of passes) recorded by detectors at Claude Smith’s Mine and Osborne's Mine during Activity Survey #3 (October)

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5 Assessment

5.0.1 The principles of this assessment are based on best practice guidelines published by the Chartered Institute of Ecology and Environmental Management (IEEM, 2006).

5.1 Constraints

Survey information

5.1.1 Weather conditions were generally good during the activity surveys, and coverage of the mine entrances was adequate for the purpose of the activity surveys. The surveyors (Simon Cope and Nicola Wheeler) are suitably experienced and licensed bat workers.

5.1.2 High rainfall during the winter of 2013/14 resulted in a very high water table in both of the mines. It is not known whether this influenced their suitability as hibernacula. Environmental data from any one year may not be representative of the prevalent microclimate over a longer period, but monitoring schemes in mines in Montgomeryshire and Shropshire, carried out by the author and other members of those bat groups, at some sites for over 20 years, have shown that this is not the deciding factor in whether bats will continue to occupy a hibernation site – once a site is known to bats, they will remain loyal despite fluctuations of up to 20% in temperature and humidity.

5.1.3 Many of the historical records from nearby sites were relatively old, which could be construed as meaning that bats were no longer present at those sites. In fact, conversations with the relevant bat groups and other bodies revealed that a lack of willing and able recorders was the reason for the lack of recent records. It has been confirmed as part of this study that most of the hibernation sites in the area are still open and accessible to bats and there is no reason to suppose that they are not still used by bats.

Equipment used

5.1.4 There were no constraints with regards to equipment.

5.2 Current Value of the site

Designated sites

5.2.1 The development site does not lie within, and is not immediately adjacent to, any designated sites. There are no sites within 5km that are designated because of bats.

Bat roosts

5.2.2 The species recorded roosting at Claude Smith’s Mine include Daubenton’s Bat, Natterer’s Bat and undifferentiated Whiskered/Brandt’s Bat. There are no publicly

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available data on the regional population sizes and trends of these species, probably partly due to the lack of historical records to base a reliable estimate on. At a national level, all of these species are widespread throughout England and their population sizes are considered to be either stable or increasing (BCT, 2014 & JNCC, 2014). None of these species are listed on the UKBAP or the Northamptonshire LBAP.

5.2.3 The mine has proven to be used by bats for a number of purposes at different times of the year: in winter for hibernation, as a day roost during the spring and as a swarming site in the autumn, and these various functions have different inherent values.

5.2.4 The geographical frame of reference for determining the contextual value of a site includes the following levels: international; UK; national; regional, county; district; local; and site-only. The different levels are not defined further in the CIEEM guidelines (IEEM, 2006), but, for the purposes of this assessment, a regional value is taken to mean the East Midlands region, and local is taken to mean within 5km of the site.

5.2.5 Hibernating bats are particularly vulnerable to disturbance - arousal at this time of year may significantly deplete their energy reserves and inclement weather can prevent them from finding alternative roosting locations. There are, however, at least six alternative hibernacula within 5km of the site, including three within 500m (see Figure 4), that have been used in the last two decades by the species found during these surveys, and at least five of these mines are confirmed as being suitable as hibernacula, so this role at Claude Smith’s Mine is considered to be of local value.

5.2.6 Swarming sites can have a long history of use by bats drawn from a wide geographical catchment, and the number of bats observed during an activity survey on any particular night are probably a small fraction of the total number using this site throughout the autumn. One study in Yorkshire showed that bats travelled from as far as 60km away, and that was in a cave-rich landscape (Glover & Altringham, 2008).

5.2.7 No equivalent study has been carried out in Northamptonshire, but it is reasonable to assume that bats may travel this far to Claude Smith’s Mine. However, there are at least five of other hibernation sites within 5km which are confirmed as being open and accessible to bats and that could be used for swarming.

5.2.8 A direct comparison of the swarming activity observed at Collyweston Slate Mine and Osborne’s Mine is not straightforward. At Osborne’s Mine, due to the shape of the entrance and the fact that the activity above and below ground was visible to the surveyor, there was much more activity in terms of bat passes recorded, whereas at Claude Smith’s Mine, much of this activity presumably went on underground, out of the view of that surveyor. For the purposes of this assessment, it is probably enough to say that both sites were used by significant numbers of bats for swarming activity.

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Therefore, this function at Claude Smith’s Mine is also considered to be of local significance.

5.2.9 The small number of transitional roosts used by bats in the spring at Claude Smith’s Mine are of only local value.

Foraging and commuting habitat

5.2.7 The lack of significant vegetation or water bodies on the site means that it is of low value as foraging habitat. The hedges at the eastern and western ends of the site may be used by the bats when commuting, but there is a moderately well-developed network of hedges in the wider countryside so these are of only local value.

5.3 Impact assessment

5.3.1 The potential impacts of the development comprise those felt in both the short- and long-term, and include any residual impacts that may continue to be felt after the development has been completed. These are summarised in Table 6. All of the predicted impacts are envisaged with no mitigation measures in place, as recommended in IEEM (2006).

5.3.2 In the absence of any mitigation measures, there are a number of ways that the re- opening of the mine could affect the bats, including: closure of access, physical destruction of roosts (mainly cracks and crevices, although bats were also seen clinging to flat walls and roofs), the infliction of physical damage to bats by mining operations (i.e., being squashed or entombed), and disturbance through mining operations (including noise, lighting, vibration, dust, fumes, and changes in temperature and/or humidity).

5.3.3 The populations of the species recorded at Claude Smith’s Mine are either stable or increasing at a national level and the numbers roosting at this mine are not a significant proportion of those populations. Therefore, the conservation status of these species will not be affected by this project and the overall negative impact on population statuses will be low. Given the proximity of other suitable sites in the area, this development is likely to have a minor negative effect on the local populations.

5.3.4 It should be borne in mind that the intended method of mining in this case will be relatively low-key, consisting of one or two people extracting the rock using a one- tonne tracked drill/excavator and then transporting it to the surface, via the adit, with a one-tonne front loader.

5.3.5 There is little published research into noise levels and the disturbance of torpid bats, but Luo et al. (2014) experimented with different types of noise and the resulting arousal of bats. All of the anthropogenic noises generated during their experiments that caused arousal were above 60 decibels, so the permitted threshold in the mitigation strategy includes a large safety margin.

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Ecological impact assessment of the development Ecological Confidence in Value Feature predictions 1 Magnitude or extent Duration Reversibility Timing and frequency

Minor negative impact on overall One-off loss when mining Hibernation site Local conservation status through direct Permanent Irreversible Probable operations start roost loss

Minor negative impact on overall One-off loss when mining Swarming site Local conservation status through direct Permanent Irreversible Certain operations start roost loss

Negligible negative impact on Transitional day One-off loss when mining Local overall conservation status Permanent Irreversible Probable roosts operations start through direct roost loss

Major negative impact on Persistent risk during mining individual bats due to physical operations if bats retain All roosting bats Local Permanent Irreversible Probable injury associated with mining access to the area being operations actively mined

Minor negative impact on Persistent risk during mining individual bats due to disturbance operations if bats retain All roosting bats Local Temporary Reversible Certain associated with mining operations access to the area being (noise, artificial lighting, etc.) actively mined

Table 6. Summary of the impact of the proposed development on the ecological features identified on site (in the absence of any mitigation measures).

1 There are no empirical data available in this case, so the certainty of the predictions are based on the expert judgement of the author. The categories are as follows: Certain: probability estimated at 95% or higher; Probable: probability estimated between 50% and 95%; Unlikely: probability estimated between 5% and 50%; Extremely unlikely: probability estimated less than 5%.

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6 Recommendations and mitigation

6.1 Further survey work

6.1.1 No further preliminary survey work is required. The surveys undertaken to date are proportionate to the development and allow the usage of the site by bats to be described adequately.

6.2 Mitigation measures

6.2.1 There are a number of factors that will affect the design of a practicable mitigation scheme, as follows:

 Bats will need to retain access to at least some of the underground areas if they are to continue to use the site. Ideally, this access will be via the existing old shaft;  Modern mine safety regulations specify at least two entrances. The through-flow of air between these will change the existing stable underground microclimate if it is not controlled;  The bats will need to be protected from physical harm and disturbance during mining operations. Collyweston Slate is traditionally extracted during the winter months, but the bats will be at their most vulnerable during this period;  The existing access route, and the cracks and crevices that bats have been observed to use should be retained if possible.

6.2.2 The principle of mitigation in the broad sense involves a hierarchy of desirable outcomes designed to maintain or promote the conservation status of the species concerned, as follows:  Avoidance – can the development be designed so that there will be no negative impacts?  Mitigation – can the development be designed to reduce the negative impacts?  Compensation – can the unavoidable impacts be compensated for?

6.2.3 Given the geology and ownership curtilage, it is not possible to carry out mining at another location. Therefore the following proposals are aimed at mitigating the predicted negative impacts of the proposed development.

Mitigation for bat roosts

6.2.4 Mining operations will be divided into two phases, each lasting five years, followed by post-mining restoration (Figures 11, 12 & 13). There will be absolutely no overlap between operational areas and areas accessible to bats at any time, and there will be no changes in temperature, humidity and airflow in the parts of the mine occupied by bats because there will only ever be one entrance that is open and accessible to them, that being the old shaft that they use now.

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Phase 1 1. All mining operations will be confined to the southern sector and bats will be prevented from entering this sector by the construction of a solid, opaque, soundproof barrier, i.e., a concrete block wall (Barrier #1). This will be constructed in the existing underground passage just south of the old shaft (but not during the hibernation period, December to February inclusive) and the barrier will be fitted with a door which can be opened to provide emergency access (for humans). These have been licensed in other mines where it was necessary to keep bats separate from mining activities (Ransome, 2011), and this will effectively seal the southern sector off from the rest of the mine. 2. Bats will be excluded from the southern passage by the incorporation of one-way doors in Barrier #1 (Figure 14) which will allow any bats to leave the southern passage while preventing them from re-entering. Four days after the barrier is put in place, the southern passage will be searched by a suitably experienced and licensed ecologist, and any bats found to be still roosting here will be relocated to the northern passage. The bats can then continue to use the existing shaft and the northern passage throughout Phase 1 (Refuge #1). 3. An adit will be driven from the west of the existing mine to link up with the south passage. In addition to the emergency door in Barrier #1, this will provide two entrances in compliance with mine safety regulations. The surface entrance to this adit will be fitted with a bat-proof door which is kept permanently closed so that bats are excluded (if ventilation is required, this can incorporate small diameter wire mesh (≤5mm mesh size). 4. The continuation of mining activity during the main hibernation period (December – February inclusive) will be evidence-led - a noise meter will be deployed near the bottom of the old shaft and work will be halted during this period if noise levels exceed 40 decibels. 5. Mining activity will only take place during daylight hours so that nocturnal activity such as swarming is not disturbed. 6. All mined material will be removed via the adit, not through the existing shaft. 7. Any floor levels in operational areas that are lowered to facilitate mining activity will be raised to align with those existing in the original mine prior to abandonment. 8. Two bat-proof dry-stone walls (filled with fine-grained material, e.g., sand) will be constructed to partition off a bat refuge in the eastern part of the southern sector. (Figure 12) These will create a physical barrier to bats during Phase 2 while also serving to muffle noise and vibrations caused by subsequent mining activities. 9. Phase 1 will be complete when all of the Collyweston Slate in the southern sector has been mined and the bat refuge has been created. The long-term stability of the new void will be ensured by the provision of suitable pillars, and a range of suitable roosting crevices will be provided in the form of stacked ‘deads’, shot-holes or cracks in the bedrock.

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Phase 2 1. A solid, opaque, soundproof barrier (Barrier #2) will be constructed in the north passage just north of the existing shaft (but not during the hibernation period, December to February inclusive). Barrier #1 will be opened to allow access for bats into Refuge #2 in the southern sector; they will have access to this refuge via their customary route (the old shaft) and be confined behind the dry-stone walls constructed during Phase 1. They will therefore remain totally separated from all mining activity. 2. Bats will be excluded from the northern passage by the use of one-way doors installed in Barrier #2, which will allow them to leave this area while preventing them from re- entering. Four days after the barrier is put in place, the northern passage will be searched by a suitably experienced and licensed ecologist, and any bats found to be roosting here will be relocated to the southern passage. The bats will then have access to the southern sector via the existing shaft (Refuge #2) and mining operations can begin in the northern sector. 3. The continuation of mining activity during the main hibernation period (December – February inclusive) will be evidence-led - a noise meter will be deployed near the bottom of the old shaft and work will be halted during this period if noise levels exceed 40 decibels. 4. Mining activity will only take place during daylight hours so that nocturnal activity such as swarming is not disturbed. 5. Any floor levels in operational areas that are lowered to facilitate mining activity will be raised to align with those existing in the original mine prior to abandonment. 6. Phase 2 will be complete when all of the Collyweston Slate in the northern sector has been mined. The long-term stability of this new void will also be ensured by the provision of suitable pillars, and a range of suitable crevices will be provided similar to those mentioned above.

Post-mining restoration

6.2.5 By way of post-mining restoration, both barriers will be removed (between June and August, when bat activity is at its lowest), the adit entrance will be permanently closed and the existing shaft will be left open to provide access to the whole of the mine for bats. A large number of crevices will be provided throughout the mine in the form of cracks in the rock and gaps among stacked ‘deads’. In the long-term, therefore, the underground habitat available to bats will be significantly extended.

Supervision by the Ecological Clerk of Works

6.2.6 A suitably qualified and experienced Ecological Clerk of Works (ECW) will be appointed, and they will be responsible for the effective implementation of this mitigation scheme - they will inspect the integrity of all bat-proof barriers, doors and dry-stone walls before bat exclusion and they will be responsible for the effective relocation of bats when necessary.

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Figure 11. Plan of Phase 1 mining operations and bat protection measures.

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Northern sector

Figure 12. Plan of Phase 2 mining operations and bat protection measures.

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Figure 13. Post-mining restoration plan: barriers removed, surface adit closed and existing shaft open. The entire area hatched in blue would be accessible to bats.

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Figure 14. Drawing of a one-way bat door. A number of these can be incorporated into the barrier blocking the passages. The netting is not stapled along the bottom edge so that the bats can crawl out. If the bat returns, it will fly straight to the slot between the planks and be stopped by the netting (taken from BCI, 2011).

Mitigation for swarming activity

6.2.4 By adhering to the measures outlined above, the suitability of the site for swarming activity will be maintained and bats will always have access to underground space via the old shaft. Phase 1 will result in a temporary reduction of the volume of that space, when the bats only have access to Refuge #1 (the longer of the two passages from the old shaft.

6.2.5 Research on the desirable attributes of swarming sites has shown that the four most significant variables controlling swarming site selection are (in order of importance): 1) chamber formation; 2) hydrological activity; 3) shelter at the entrance, and; 4) length of underground passage (Glover & Altringham, 2008). The first three of these variables will not be affected by the proposed mining activity at Claude Smith’s Mine. The length of underground passage will be reduced by approximately 30% during Phase 1, when the bats only have access to Refuge #1, but this will be

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remedied during Phase 2, when the bats have access to the larger volume of Refuge #2. There is no reason to suppose that this temporary reduction will be detrimental to the suitability of the site as a swarming venue, because swarming activity was also observed at the nearby Osborne’s Mine which is a significantly smaller mine. In the post-restoration phase, bats will have access to the whole mine which will be considerably larger than the space they have now.

Mitigation for foraging and commuting habitat

6.2.6 The above-ground habitats in the immediate vicinity of the existing mine entrance are poorly suited to bats, consisting as they do of hard-standing and buildings, with a two metre high chain link fence surrounding the old shaft. There will be a negligible impact on these habitats during the operational phase, so no mitigation will be necessary.

6.2.7 Any additional outdoor security lighting will be directed away from the existing shaft. All lights should be automated using Passive InfraRed (PIR) sensors, which must also be directed away from the old shaft

Enhancement for commuting and foraging habitat

6.2.8 As part of the post-mining restoration, and in order to facilitate the passage of bats to and from the existing mine entrance, a corridor of site-native shrubs will be planted that will lead from the shaft to the open grassland immediately to the north of the site. This will consist of at least two rows of shrubs, and the corridor will be at least 2m wide.

Post-commencement monitoring

6.2.9 A proportionate level of post-commencement monitoring will be carried out to ascertain the levels of usage of the site by bats during mining operations. The surveys will be carried out in accordance with the schedule of work outlined in Table 7. In the event of a significant decrease in the usage of the site by bats, mining activity will be halted pending further investigation into the reasons. The records of any bats found will be submitted to the local Biological Records Centre.

6.2.10 Numbers of hibernating bats will naturally vary from year to year. The maintenance of suitable conditions will therefore be monitored by measuring the temperature and humidity of the underground space in the interval between the swarming survey and the winter surveys (a period of approximately three or four months).

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Phase Event No. Timing Activity

Year 1 Install Barrier #1. Start excavating adit and install bat-proof door on adit 1 (October/November, 2015) entrance. Year 1 Ecological Clerk of Works (ECW) checks integrity of Barrier #1 & bat-proof door on 2 (October/November, 2015) adit. Bats are excluded from southern sector Year 1 (2015) 3 ECW relocates bats from southern sector to Refuge #1 (4 days after Event 2)

4 Years 1 & 2 (2015 & 2016) Adit connected to southern sector of existing mine. Mining carried out

Year 2 5 ECW carries out hibernaculum surveys (January/February, 2016) Year 2 Phase 1 6 ECW carries out activity survey in swarming season (Autumn, 2016)

7 Year 3 (2017 Mining carried out

8 Year 4 (2018) Mining carried out

Year 4 9 ECW carries out hibernaculum surveys (January/February, 2018) Year 4 10 ECW carries out activity survey in swarming season (Autumn, 2017)

11 Year 5 (2019) Mining carried out. Bat-proof walls constructed to form Refuge #2.

Year 6 12 Install Barrier #2. (March/April, 2020) Year 6 ECW checks integrity of Barrier #2 and removal of Barrier #1. Bats are excluded 13 Phase 2 (March/April, 2020) from northern sector (Refuge #1) Year 6 (2020) 14 ECW relocates bats from northern sector to Refuge #2 (4 days after Event 14)

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Phase Event No. Timing Activity

15 Year 6 (2020) Adit connected to northern sector of existing mine. Mining carried out

16 Year 7 (2021) Mining carried out Year 7 17 ECW carries out hibernaculum surveys (January/February, 2021)

Year 7 18 ECW carries out activity survey in swarming season (Autumn, 2021)

Phase 2 19 Year 8 (2022)) Mining carried out

20 Year 9 (2023) Mining carried out

Year 9 21 ECW carries out hibernaculum surveys (January/February, 2023) Year 9 22 ECW carries out activity survey in swarming season (Autumn, 2023) Year 10 (2024) 23 Mining carried out (June - August) Year 10 24 ECW checks Barriers #1 & #2 are removed and adit is permanently closed. (end-August, 2024) Year 11 Restoration 25 ECW carries out activity survey in swarming season (Autumn, 2025) Year 12 26 ECW carries out hibernaculum surveys (January & February, 2026)

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Predicted impacts after the implementation of the mitigation measures

6.2.11 There will be a reduction in the volume of underground space available to bats during Phase 1, although it is not thought that this will significantly affect the ability of the site to host similar numbers of hibernating and swarming bats because smaller sites than this are monitored by the author and are known to be used by much larger numbers of hibernating bats. During Phase 2 there will be an expansion in the volume available to bats.

6.2.12 The restrictions on the timing of mining activity will ensure the separation of the bats when they are particularly vulnerable, i.e., after dark and during the hibernation and swarming seasons.

6.2.13 The physical separation of bat refuges from working areas by the use of bat-proof doors and other barriers will eliminate the possibility of physical harm to bats.

6.2.14 Links with the surrounding countryside will be enhanced by the planting of a new hedgerow between the old shaft and the nearby semi-natural habitat in the Restoration phase. These residual impacts are summarised in Table 8.

Requirement for Habitats Regulations (EPS) licences

6.2.15 It is thought that all of the adverse impacts can be overcome if the mitigation measures outlined above are adopted in full. However, existing bat roosts will be destroyed and bats may be disturbed and relocated so a site-specific EPS Licence will be necessary.

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Confidence in Ecological impact assessment of the development: residual impacts predictions 1 Ecological Value Feature Magnitude or extent

Medium–term: possible temporary minor negative impact due to reduction in length of Medium-term: Hibernation site Local underground passage during Phase 1. probable Long-term: major positive impact due to increased size and complexity of underground space. Long-term: certain

Medium –term: possible temporary minor negative impact due to reduction in length of Medium-term: Swarming site Local underground passage during Phase 1. probable Long-term: major positive impact due to increased size and complexity of underground space. Long-term: certain

Medium –term: possible temporary minor negative impact due to reduction in length of Medium-term: Transitional day Local underground passage during Phase 1. probable roosts Long-term: major positive impact due to increased size and complexity of underground space. Long-term: certain

Negligible negative impact due to the process of exclusion and relocation. All roosting bats Local Moderate positive impact due to the establishment of a dark wildlife corridor connecting the Certain old mine shaft to the surrounding countryside.

Negligible negative impact due to disturbance associated with mining operations. All roosting bats Local Moderate positive impact due to the establishment of a dark wildlife corridor connecting the Certain old mine shaft to the surrounding countryside.

Table 8. Summary of the residual impacts of the proposed development on the ecological features identified on site if mitigation measures are followed.

1 Certain: probability estimated at 95% or higher; Probable: probability estimated between 50% and 95%; Unlikely: probability estimated between 5% and 50%; Extremely unlikely: probability estimated less than 5%.

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7 References

BCI (Bat Conservation International) (2011) ‘Excluding bats from Vermont residences – a guide to best practice.’ BCI, Austin, Texas, USA.

BCT (Bat Conservation Trust) (2014) ‘Species Population Trends’ http://www.bats.org.uk/pages/species_population_trends.html [11/14]

English Heritage (2005) 'Stone Slate Roofing: Technical Advice Note' English Heritage, London.

Glover, A.M. & Altringham, J.D. (2008) ‘Cave selection and use by swarming bat species’. Biological Conservation, vol. 141, pp. 1493-1504.

Gunnel, K., Murphy, B, & Williams, C. (2013) ‘Designing for Biodiversity – A technical guide for new and existing buildings.’ 2nd Edition, RIBA, London.

Hundt, L. (2012) 'Bat Surveys: Good Practice Guidelines.' Bat Conservation Trust, London.

IEEM (Institute of Ecology and Environmental Management) (2006) 'Guidelines for Ecological Impact Assessment in the United Kingdom.' Winchester.

JNCC (Joint Nature Conservation Committee) (2013) 'Individual Species Reports - 3rd UK Habitats Directive reporting 2013.' http://jncc.defra.gov.uk/page-6391 [11/2014]

Luo, J., Markus-Clarin, B., Borissov, I.M. & Siemers, B.M. (2014) ‘Are torpid bats immune to anthropogenic noise?’ Journal of Experimental Biology, vol. 217, pp. 1072-1078.

Middleton, N., Froud, A. & French, K. (2014) ‘Social calls of the bats of Britain and Ireland’ Pelagic Publishing, Exeter.

Mitchell-Jones, A.J. (2004) ‘Bat mitigation guidelines.’ English Nature, Peterborough.

Mitchell-Jones, A.J. & McLeish, A.P. (2004) ‘Bat Workers Manual.’ 3rd Edition, JNCC, Peterborough.

NCC (Northamptonshire County Council) (2014) 'Minerals and Waste Local Plan' NCC, Northampton.

Ransome, R. (2011) ‘Bat mitigation Scheme for Park Lane Mine and Method Statement’. Unpublished report for Wiltshire planning application N/09/02158/WCM.

Russ, J. (2012) ‘British Bat Calls: A guide to species identification’ Pelagic Publishing, Exeter.

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Appendix 1 Historical records (see PDF’s)

Not for general publication due to sensitive information

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Appendix 2 Photographs

(All photographs of bats were taken without a flash, causing no additional disturbance)

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Old shaft

Photo 1. View of the Industrial Estate looking towards the old shaft.

Photo 2. View of the industrial estate showing the hard standing, sheds and stockpiled materials that cover most of the site.

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Photo 3. The top of the mine old shaft - an unpromising location cut off from semi-natural vegetation and surrounded by fences and scaffolding.

Photo 4. Typical section of the existing underground passage, with the old working face straight ahead and stacked ‘deads’ on the left. This photo was taken on the preliminary scoping survey; during the following winter the floor of the passage was mostly submerged.

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Photo 5. Crevices between the stacked 'deads' appear to make ideal roosting locations for bats, although only one individual was recorded in one of these during the winter surveys.

Photo 6. Bat droppings were scattered sparsely over the floor throughout the mine, occasionally slightly more concentrated under what may have been roosting sites.

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Photo 7. A Daubenton’s Bat recorded near the north end of the north passage during the preliminary site survey (November, 2013).

Photo 8. A Whiskered/ Brandt’s Bat recorded in the chamber just north of the old shaft during the preliminary site survey (November, 2013).

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Photo 9. One Natterer’s Bat and four indeterminate Myotids crammed into a crack near the base of the old shaft, recorded during the second winter survey (February, 2014).

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Appendix 3 Raw survey data

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Claude Smith’s Mine Claude Smith’s Mine Number Number Date Time Species Date Time Species of files of files 31/01/14 17:35 Mn 1 16:59 Mn 1 01/02/14 21:36 Mn 1 17:52 Mn 1 17:24 Mn 1 18:39 Mn 1 02/02/14 17:25 Mn 1 19:18 Mn 1 18/02/14 21:09 Mn 1 22:40 Md 1 17:30 Mn 2 22:41 Mn 1 17:33 Mn 1 22:53 Mn 1 03/02/14 17:46 Mn 1 22:54 Mn 1 18:17 Myotis 1 00:16 Mn 3 18:18 Myotis 1 00:52 Mn 1 00:32 Myotis 1 00:53 Mn 1 04:52 Mn 1 19/02/14 07:47 Mn 1 04/02/14 17:03 Mn 1 18:09 Myotis 1 19:58 Mn 1 18:50 Mn 1 16:15 Mn 1 23:11 Mn 1 06/02/14 19:17 Mn 1 01:50 Mn 1 08:44 Mn 1 01:50 Myotis 1 21:15 Mn 1 02:23 Mn 1 08/02/14 22:08 Mn 2 03:06 Mn 1 22:19 Mn 3 20/02/14 03:06 Myotis 1 10/02/14 08:23 Mn 1 21:33 Mn 1 17:18 Mn 1 23:04 Mn 2 17:51 Mn 2 23:05 Mn 1 17:53 Mn 2 23:29 Mn 1 11/02/14 17:55 Mn 1 21/02/14 00:04 Mn 1 18:01 Mn 1 18:05 Mn 1 20:38 Mn 1 Claude Smith’s Mine 06:59 Myotis 1 Number Date Time Species 07:02 Myotis 1 of files 13/02/14 17:03 Mn 2 17/04/14 No bats recorded 17:51 Mn 1 19:48 Mn 1 14/02/14 17:43 Mn 1 Claude Smith’s Mine 16:59 Mn 1 Number Date Time Species 15/02/14 19:24 Md 1 of files 19:24 Mn 1 03:01 Ppip 1 17:55 Mn 1 03:02 Ppip 1 18:32 Mn 1 03:36 Myotis 1 16/02/14 19:43 Mn 1 04/07/14 03:38 Myotis 1 19:44 Mn 1 03:46 Nn 1 20:41 Mn 1 03:59 Nn 1 01:44 Mn 1 04:00 Nn 1 17/02/14 03:09 Mn 1 19:07 Mn 1 03:32 Mn 1 18/02/14 03:34 Mn 1

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Claude Smith’s Mine Osborne’s Mine Number Number Date Time Species Date Time Species of files of files 21:11 Myotis 3 20:46 Mmys 10 21:12 Myotis 3 20:47 Mmys 10 21:13 Myotis 1 20:48 Mmys 12 21:14 Mn 1 20:49 Mmys 5 21:14 Myotis 1 20:50 Mmys 10 21:18 Mn 1 20:51 Mmys 12 21:20 Mn 1 20:52 Mmys 10 21:20 Myotis 1 20:53 Mmys 12 21:23 Mn 1 20:54 Mmys 9 21:24 Mn 1 20:55 Mmys 11 21:25 Myotis 2 20:56 Mmys 11 21:26 Myotis 4 20:57 Mmys 10 21:29 Mn 1 20:58 Mmys 11 03/10/14 21:30 Mn 3 20:59 Mmys 11 21:32 Mn 1 21:00 Mmys 10 21:38 Myotis 1 21:01 Mmys 11 21:46 Myotis 1 21:02 Mmys 11 21:51 Myotis 1 21:03 Mmys 12 22:19 Myotis 3 21:04 Mmys 11 22:22 Mn 1 21:05 Mmys 11 22:22 Myotis 1 21:06 Mmys 10 22:23 Mn 1 21:07 Mmys 5 22:24 Mn 2 21:08 Mmys 9 22:26 Mn 1 17/04/14 21:09 Mmys 7 22:27 Mn 2 21:10 Mmys 8 22:30 Mn 1 21:11 Mmys 5 22:35 Mn 1 21:12 Mmys 9 21:13 Mmys 9 21:14 Mmys 3 Osborne’s Mine 21:15 Mmys 3 Number 21:16 Mmys 8 Date Time Species of files 21:17 Mmys 6 20:28 Ppip 6 21:18 Mmys 5 20:29 Ppip 10 21:19 Mmys 6 20:30 Ppip 13 21:20 Mmys 6 20:31 Ppip 13 21:21 Mmys 7 20:36 Ppip 3 21:22 Mmys 6 20:37 Ppip 15 21:23 Mmys 9 20:38 Ppip 14 21:24 Mmys 4 17/04/17 20:39 Ppip 15 21:25 Mmys 9 20:40 Mmys 3 21:26 Mmys 7 20:40 Ppip 12 21:27 Mmys 9 20:41 Mmys 10 21:28 Mmys 8 20:42 Mmys 12 21:29 Mmys 10 20:43 Mmys 11 21:30 Mmys 7 20:44 Mmys 5 21:31 Mmys 7 20:45 Mmys 7 21:32 Mmys 8

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Osborne’s Mine Osborne’s Mine Number Number Date Time Species Date Time Species of files of files 21:33 Mmys 8 02:47 Ppip 4 21:34 Mmys 9 02:54 Ppip 3 21:35 Mmys 10 02:55 Ppip 1 21:36 Mmys 10 02:56 Ppip 3 21:37 Mmys 9 03:00 Ppip 2 21:38 Mmys 5 03:03 Ppip 1 21:39 Mmys 7 03:31 Ppip 2 21:40 Mmys 5 03:39 Md 4 21:41 Mmys 9 03:39 Myotis 1 21:42 Mmys 10 03:40 Md 2 21:43 Mmys 9 03:40 Myotis 2 21:44 Mmys 9 03:41 Md 5 21:45 Mmys 10 03:42 Md 3 21:46 Mmys 8 03:42 Myotis 1 21:47 Mmys 9 03:43 Md 2 21:48 Mmys 8 03:43 Myotis 2 21:49 Mmys 5 03:44 Md 4 17/04/14 21:50 Mmys 8 03:45 Md 4 21:51 Mmys 7 03:45 Myotis 1 21:52 Mmys 10 03:46 Md 4 21:53 Mmys 8 03:46 Myotis 1 21:54 Mmys 8 03:47 Md 4 21:55 Mmys 11 04/07/14 03:48 Md 2 21:56 Mmys 11 03:49 Md 5 21:57 Mmys 11 03:50 Md 5 21:58 Mmys 8 03:51 Md 4 21:59 Mmys 9 03:51 Ppip 2 22:00 Mmys 9 03:53 Md 4 22:01 Mmys 10 03:53 Myotis 1 22:02 Mmys 6 03:54 Md 4 22:03 Mmys 9 03:55 Md 4 22:04 Mmys 9 03:55 Myotis 1 22:05 Mmys 10 03:56 Md 3 22:06 Mmys 8 03:56 Myotis 1 22:07 Mmys 12 03:57 Md 3 03:57 Myotis 1 03:58 Md 3 Osborne’s Mine 03:58 Myotis 2 Number 03:59 Md 4 Date Time Species of files 03:59 Myotis 1 02:41 Ppip 8 04:00 Md 2 02:42 Ppip 6 04:00 Myotis 2 02:45 Md 1 04:01 Md 3 04/07/14 02:45 Myotis 3 04:01 Myotis 1 02:46 Md 2 04:02 Myotis 3 02:46 Myotis 2 02:46 Ppip 1

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Osborne’s Mine Osborne’s Mine Number Number Date Time Species Date Time Species of files of files 20:22 Mn 1 21:01 Mn 1 20:22 Myotis 1 21:01 Myotis 1 20:25 Mn 1 21:02 Mbr 1 20:25 Myotis 2 21:02 Md 1 20:26 Md 1 21:02 Mmys 1 20:26 Mn 2 21:03 Mbr 2 20:27 Md 2 21:03 MmysMbr 3 20:27 Mn 2 21:03 Mn 2 20:28 Myotis 1 21:04 Md 1 20:31 Myotis 1 21:04 Mn 2 20:32 MmysMbr 1 21:04 Myotis 2 20:33 Mmys 1 21:05 Mn 1 20:33 Myotis 2 21:07 Mbr 1 20:36 Mbr 1 21:07 Md 1 20:36 MmysMbr 2 21:08 Mbr 1 20:37 MmysMbr 4 21:08 Mn 2 20:38 Mbr 1 21:09 Mmys 1 20:38 Mmys 1 21:09 Myotis 1 20:38 MmysMbr 3 21:10 Myotis 1 20:38 Mn 1 21:11 Md 1 20:39 Mbr 1 21:11 Myotis 2 20:39 MmysMbr 1 21:12 Myotis 3 20:39 Mn 1 21:13 Myotis 1 03/10/14 20:39 Myotis 3 03/10/14 21:15 Myotis 5 20:46 Md 3 21:16 Myotis 2 20:49 Md 1 21:17 Md 1 20:49 Mmys 1 21:17 Mn 3 20:49 MmysMbr 2 21:17 Myotis 1 20:50 Mbr 1 21:18 Mn 1 20:50 Md 2 21:18 Myotis 2 20:50 MmysMbr 1 21:20 Mmys 1 20:51 Mbr 4 21:20 Mn 3 20:54 Myotis 1 21:20 Myotis 1 20:57 Mn 1 21:21 Md 1 20:58 Md 1 21:21 MmysMbr 2 20:58 Myotis 1 21:21 Mn 1 20:59 Md 3 21:21 Myotis 1 20:59 Mmys 1 21:22 Md 1 20:59 Mn 1 21:22 MmysMbr 1 20:59 Myotis 1 21:22 Myotis 3 21:00 Md 1 21:23 Myotis 2 21:00 Mmys 1 21:24 Mn 1 21:00 Mn 1 21:24 Myotis 3 21:00 Myotis 2 21:25 Md 1 21:01 Mbr 1 21:25 MmysMbr 2 21:01 Md 1 21:25 Mn 1 21:01 Mmys 1 21:26 Mbr 1

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Osborne’s Mine Osborne’s Mine Number Number Date Time Species Date Time Species of files of files 21:26 Md 1 21:39 Mn 2 21:26 Mn 3 21:39 Myotis 3 21:26 Myotis 3 21:40 Md 3 21:27 Mbr 1 21:40 MmysMbr 2 21:27 Md 1 21:40 Mn 4 21:27 Myotis 4 21:40 Myotis 3 21:28 Mbr 1 21:41 Mbr 1 21:28 Md 2 21:41 Md 4 21:28 Mn 1 21:41 MmysMbr 2 21:28 Myotis 1 21:41 Myotis 4 21:29 Mbr 3 21:42 Md 2 21:29 Md 3 21:42 MmysMbr 4 21:29 MmysMbr 1 21:42 Mn 2 21:29 Mn 1 21:42 Myotis 5 21:30 Mbr 1 21:43 Mbr 1 21:30 Md 4 21:43 Myotis 3 21:30 Mmys 1 21:44 Md 1 21:30 Myotis 1 21:44 Mn 1 21:31 Mbr 1 21:44 Myotis 4 21:31 Md 3 21:45 Md 3 21:31 MmysMbr 1 21:45 MmysMbr 1 21:32 Md 4 21:45 Mn 3 21:32 MmysMbr 2 21:45 Myotis 4 03/10/14 21:32 Myotis 2 03/10/14 21:46 Md 1 21:33 Mbr 1 21:46 Mn 3 21:33 Md 3 21:46 Myotis 3 21:33 Mmys 1 21:47 Md 2 21:33 Myotis 2 21:47 Mn 1 21:34 Md 2 21:47 Myotis 3 21:34 Mn 3 21:48 Md 2 21:34 Myotis 3 21:48 MmysMbr 1 21:35 Md 3 21:48 Mn 1 21:35 Myotis 1 21:48 Myotis 1 21:36 Md 3 21:49 Myotis 2 21:36 MmysMbr 1 21:50 Md 1 21:36 Mn 1 21:50 MmysMbr 2 21:36 Myotis 1 21:50 Mn 1 21:37 Mbr 1 21:50 Myotis 2 21:37 Md 4 21:51 Md 1 21:37 Mmys 1 21:51 Mmys 1 21:37 Mn 2 21:51 Mn 2 21:37 Myotis 1 21:51 Myotis 3 21:38 Md 2 21:52 Mbr 1 21:38 MmysMbr 2 21:52 Mn 3 21:38 Myotis 1 21:52 Myotis 3 21:39 Md 1 21:53 Md 4 21:39 MmysMbr 1 21:53 Myotis 1

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Osborne’s Mine Osborne’s Mine Number Number Date Time Species Date Time Species of files of files 21:54 Md 1 22:10 Myotis 3 21:54 Mn 2 22:11 Mbr 1 21:55 Md 3 22:11 MmysMbr 1 21:55 Mn 2 22:11 Mn 1 21:55 Myotis 3 22:11 Myotis 2 21:56 Mbr 1 22:12 Md 2 21:56 Md 4 22:12 MmysMbr 1 21:56 MmysMbr 1 22:12 Mn 3 21:56 Mn 2 22:12 Myotis 3 21:56 Myotis 2 22:13 Md 2 21:57 Mbr 1 22:13 Mn 1 21:57 Md 4 22:13 Myotis 2 21:57 Mn 4 22:14 Md 2 21:57 Myotis 4 22:14 Myotis 5 21:58 Md 3 22:15 Md 2 21:58 Mmys 1 22:15 MmysMbr 1 21:58 MmysMbr 1 22:15 Myotis 3 21:58 Mn 1 22:16 Md 2 21:59 Md 1 22:16 Myotis 4 21:59 MmysMbr 1 22:17 Md 2 21:59 Mn 1 22:17 Myotis 5 22:00 Mn 3 22:18 Md 1 22:01 Md 1 22:18 Myotis 4 03/10/14 22:01 Mn 1 03/10/14 22:19 Md 1 22:02 Mn 3 22:19 MmysMbr 1 22:03 Md 1 22:19 Myotis 3 22:03 Mn 3 22:20 Md 3 22:03 Myotis 2 22:20 Mmys 1 22:04 Md 3 22:20 Myotis 3 22:04 Mn 1 22:21 Myotis 3 22:04 Myotis 2 22:22 Md 4 22:05 Md 2 22:22 Myotis 2 22:05 Mn 2 22:23 Md 4 22:05 Myotis 4 22:23 Mn 2 22:06 Md 4 22:23 Myotis 1 22:06 Mn 1 22:24 Md 1 22:06 Myotis 1 22:24 Mn 2 22:07 Md 4 22:24 Myotis 5 22:07 Myotis 1 22:25 Md 2 22:08 Md 3 22:25 Mn 3 22:08 Mn 3 22:25 Myotis 3 22:08 Myotis 1 22:26 Md 2 22:09 Md 2 22:26 Myotis 4 22:09 Mn 1 22:27 Md 1 22:09 Myotis 4 22:27 Myotis 3 22:10 Md 1 22:28 Md 1 22:10 Mn 2 22:28 Mn 2

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Osborne’s Mine Osborne’s Mine Number Number Date Time Species Date Time Species of files of files 22:28 Myotis 3 22:33 Myotis 4 22:29 Md 4 22:34 Md 4 22:29 Mn 3 22:34 Myotis 4 22:29 Myotis 1 22:35 Md 5 22:30 Md 2 22:35 Myotis 1 22:30 Mn 4 22:36 Md 5 22:30 Myotis 3 22:36 Mn 4 03/10/14 03/10/14 22:31 Mn 3 22:36 Myotis 4 22:31 Myotis 4 22:37 Md 4 22:32 Md 1 22:37 Mn 3 22:32 Mn 2 22:37 Myotis 1 22:32 Myotis 3 22:38 Md 2 22:33 Md 2 22:38 Mn 1 22:33 Mn 2 22:38 Myotis 3

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Appendix 4 Sample sonograms

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Figure 13. Screen-shot of a sonogram, with frequency on the vertical axis and time along the horizontal axis. The hockey stick shaped calls are diagnostic of all Pipistrelle species, and the flatter (qCF) part of the call at around 45 kHz indicates a Common Pipistrelle. The steeper calls at 1.73 seconds are a ‘feeding buzz’, produced when the bat is close to its prey (expansion scale: F7, compressed to remove spaces between calls, filtered to remove most non-bat noise).

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Natterer's calls Daubenton's calls

Natterer's calls Daubenton's calls

Figure 14. Calls of a Natterer's and a Daubenton's Bat in the same sonogram. The calls (above-left) show the typical near-vertical (FM) sweep of all Myotid species, but the differences between the two sets of calls are clear. The split-screen on the right-hand side is an analysis of the slope of the corresponding calls on the left, and the range of octaves per second coupled with the call shape are indicative of the species (F9, compressed, filtered).

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Social call Echolocation call

Figure 15. During Activity Survey #3 (October) many social interactions between bats were observed, often coinciding with the detection of 'social calls'. The sonogram above shows various 'Type C' social calls of a Daubenton's Bat recorded during a chase, in between the normal echolocation calls of Daubenton's and another Myotis species (F8, compressed, filtered).

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Figure 16. Myotid echolocation calls with many small-scale kinks and a slope almost entirely between 300 and 700 octaves per second (OPS) are most likely to be from a Whiskered Bat (approximately 60% confidence level) (F9, compressed, filtered).

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Figure 17. Often indistinguishable from the calls of other Whiskered Bats (sensu lato), these calls have been attributed to a Brandt's Bat due to the restricted slope range (almost all below 500 OPS) and the many small-scale kinks (approximately 60% confidence level) (F9, compressed, filtered).

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