Artificial badger sett design

Background and industry context

Badgers and their setts are protected under The Protection of Badgers Act 1992^[1]. The Act allows for Natural England to grant licences for permitted development in England. Where permitted development is the purpose, persons can be licensed to interfere with badger setts; the most common form being via the eviction and exclusion of badgers from setts. The aim of any badger sett exclusion exercise is to facilitate lawful development while retaining the affected animals within the territory of their social group.

These licences have conditions for how the works will be done sensitively to reduce the impact on badgers as far as possible, how the impacts will be mitigated and what monitoring is required to check the success of mitigation.

Approach

HS2 Ltd were issued a route-wide badger licence from Natural England for Phase One of the scheme (London to West Midlands) in 2017. Natural England have published the current badger licence issued to HS2 Ltd (WML-OR24)^[2].

HS2 Ltd employ contractors to manage and carry out badger survey, mitigation, and monitoring, who in turn employ specialist ecological consultants.  To carry out work under the HS2 route-wide badger licence, ecologists need to evidence their competency and experience of carrying out similar work and are individually approved by HS2 as Additional Appointed Persons (AAP). 

Method statements are produced for each badger territory or sett where licensable works are required which detail the impacts to badgers and the appropriate mitigation design to comply with the licence.  These method statements are reviewed by the HS2 ecology team against a strict checklist to ensure the assessments made and measures proposed are compliant with the licence.  The AAP are responsible for supervising licensable works on site. 

Under the licence an artificial badger sett (ABS) needs to be provided where closure or destruction of a sett, usually a main sett, results in there being no suitable alternative sett for the excluded badgers within their existing territory. The ABS are to ensure the badger territory has provision to a main breeding sett when the natural sett is closed. Badgers may then build a new sett elsewhere or expand another existing sett within their territory.

Main setts usually have many entrances with large spoil heaps and look well used. They usually have well used paths to and from the sett and between sett entrances and are normally used for breeding within a badger territory.

Under the HS2 route-wide badger licence, where an ABS has been constructed, action to exclude badgers from their natural sett may only begin once there is evidence that badgers have discovered the ABS and can only be done between July and November, outside of the badger breeding season. To ensure badgers are not present in existing setts, the activity of badger sett entrances is monitored, using standard techniques such as infra-red cameras and field signs, footprints and badger guard hair, for a minimum period of 21 days before action is taken to destroy an existing sett or securely close access to it.

The licence requires that ‘At least 20% (rounded up to the nearest whole number) of artificial setts constructed must be monitored for use by badgers at least twice a year for up to 2 (two) years following the closure and destruction of the original sett.’ The ABS were monitored by experienced ecologists using a range of standard methods, such as infra-red motion sensitive cameras at the tunnel entrances and looking for badger paw prints and badger hair in and around the ABS entrance. Condition of the ABS was also noted during monitoring indicating if the ABS is suitable for use by badgers or whether any maintenance or remedial action is required.

Interaction with agricultural land

There was concern from landowners that the mitigation works for badgers, and disturbance of badgers from HS2 construction, would increase the risk of the spread of bovine tuberculosis (bTB) onto cattle farms.

A Veterinary Risk Assessment, commissioned by Natural England and undertaken by the Animal Plant Health Agency (APHA), found that “Based on a qualitative assessment of the current evidence, the likelihood that badger sett closures along the London-West Midlands-Staffordshire railway line could lead to an increase in the incidence of TB in cattle has been assessed as low, subject to a number of key uncertainties”.

Badger mitigation does not involve actively moving badgers. The mitigation is a standard good practice approach based on excluding badgers from an existing sett and allowing them to move themselves to another sett within their territory. However, biosecurity, including bTB risk, is a core consideration at HS2 and some of the badger mitigation has been designed without full badger territory boundaries being known. The HS2 Contractors are required to assess biosecurity requirements at each location and where necessary prepare and implement a Biosecurity Management Plan. Where it is considered that there is a significant remaining risk, despite the proposed measures, these are discussed with the livestock owner to ascertain the best options at that location. Further information can be found at the TB Hub – the home of UK TB information^[3].

Monitoring outcomes

Thirty-two ABS were built across Phase One of the scheme between 2018 and 2021: most of these in 2020 and 2021. All setts were built at least six months in advance of natural sett closure.

Four ABS were built but not required to act as mitigation for closed setts. Two of these were due to a change in subsequent survey evidence such that the sett to be closed was no longer considered to be a main sett. Two were due to changes in the scheme design resulting in saving the natural main setts. These ABS were left in place but were not monitored as part of licensable works as they had not been used as mitigation.

Of the remaining 28 ABS, six needed reconstruction or remedial action:

• One ABS needed replacing, and one needed remediating due to tunnel collapses because of weakness in more sustainable materials used in a limited number of ABS construction (see Sustainable badger sett design case study in supporting materials).
• Two ABS were replaced following flood damage.
• One ABS was replaced due to lack of occupation.
• One ABS was constructed in 2020 but, following further baseline surveys of the badger group, was considered too small so a second ABS was built in 2021.

All ABS showed signs of activity and use within 6 months of their build or before the closure of the setts they were mitigating for. HS2 has monitored 26 ABS for at least two years, more than required under the route-wide licence. The ABS were constructed and monitored in different years between 2018 and 2023, therefore the monitoring results are discussed as monitoring year 1 and year 2 etc. rather than as specific years.

Of the 26 ABS which were monitored over two years or more:

• 18 showed evidence of use in year 1; of these five showed no evidence of use in year 2. Those ABS not used in year 2 were noted as in good condition and suitable for badgers apart from one where surveyors noted, during a December monitoring visit, that the ground was sodden and there was likely flooding of the sett. One of the setts not used in year 2 had evidence of badger pathways into the ABS but no evidence was found on camera, indicating it may be occasionally used.
• 18 showed evidence of use in year 2, including five which had not shown use in year 1, although the ABS were noted as in good condition and suitable for use by badgers.
• Of eight ABS monitored in year 3, six were in use and five had showed evidence of use in all three monitoring years:
  • One ABS had no evidence of use in year 1 but was used in years 2 and 3.
  • One ABS had use in year 1 but not in years 2 and 3 although in year 3 there was evidence of badger pathways into the ABS but no evidence was found on camera, indicating it may be occasionally used.
  • The remaining ABS monitored in year 3 had evidence of use in year 1 and 2 but not in year 3 although in year 3 badgers had built a new active 11-hole main sett adjacent to the ABS. It is not known if the two setts are connected underground.
• Two ABS had four-years monitoring and showed evidence of use in all four years.
• Two ABS showed no evidence of use at the time of monitoring in year 1 or 2, although badgers were still found to be very active in their territories and one ABS had a small amount of badger bedding in the entrance, but badgers were not recorded on camera, indicating the ABS was occasionally used.

As the monitoring was of activity at the ABS and not within the wider badger territory, it is not known whether some badgers from ABS showing no evidence of use had left to build new setts in the area or made use of retained setts in the wider countryside.

Learnings and recommendations

Location

ABS should be located within the badger territory, as close to the existing main sett as possible (usually within 100m) and alongside paths known to be used by badger. One ABS was located almost 500m from the main sett, due to land restrictions, and was not used. Following redesign of the scheme, the ABS was reconstructed within 60m of the main sett and subsequently had evidence of badger use. It is important, where the ABS must be constructed at distance from the existing main sett, that the badgers are encouraged to find the ABS using trails of food, especially if the ABS is not on an existing badger path.

In many cases there was limited space in the limits of land to be acquired and used for construction and operation of HS2, as defined in the HS2 Act^[4], which would not be affected by on-going construction works. The ABS tended to be built on the edge of the Act Limits and in some cases, this needed a more linear ABS design. Network Rail^[5] badger sett creation design, in conjunction with the guidance of relevant engineers, can be used if an ABS is to be created within an embankment, where concrete chambers are required for load bearing. On HS2 a modified linear ABSdesign was used in one location in Buckinghamshire due to limitations of land within the HS2 Act Boundary.

On Phase 2a, indicative ABS designs and the locations for them were chosen in 2022, prior to any licensable works to close existing setts and based on limited survey data. This was to derisk some programme critical works by producing early designs. Where information on the boundaries of badger territories was not available, an assessment of likely territories was made using habitat information and the ABS were located within 150m of the existing main sett and not close to other ‘assumed’ territories. No ABS have been constructed on Phase 2a.

ABS are best located away from publicly accessible areas. The HS2 project has had issues with members of the public illegally interfering with and damaging HS2 badger mitigation works, such as removing mesh and one-way gates over existing sett entrances. In these cases, HS2 and our Contractors needed to work cooperatively with the site security teams and the police local wildlife liaison officers. The first ABS constructed on HS2 was in an area which could be seen from a Public Right of Way, due to restricted land availability. The design included planting of scrub, onto and around the ABS, to help screen the sett. The planting is subject to a 10-year management regime. The ABS, constructed in 2018, showed evidence of regular badger use three years after it was built (although not formally monitored after two years). Few ABS had associated planting as part of the design, as the location chosen tried to integrate with retained vegetation, such as scrub and hedgerows. The chamber roofs or a wider area above them can be covered with galvanised weldmesh and geotextile to deter illegal digging for badgers. This will also reduce unwanted soil ingress into the chambers and tunnels.

Timing

Under the Natural England licence, evidence of badgers using the ABS is needed before the existing sett can be closed. It is difficult to predict how long it will take badgers to find and start using the ABS. All ABS on HS2 were constructed at least six months in advance of when existing setts needed closing, and in some cases trails of food were used to encourage ABS use and reduce programme risk.

At programme critical locations, some ABS were designed and built before surveys were completed. One ABS was constructed in 2020 as a precaution for a suspected main sett prior to full survey information being available. A precautionary assessment was used to choose the location and the ABS design was based on survey data available and ecologists experience. Following land access and further surveys the existing sett was established as a subsidiary with no occupation by badger. Therefore, the ABS was not required for mitigation under licence and no monitoring was carried out although the ABS was retained, in good condition and suitable for use by badgers.

Another ABS was constructed in 2020, also based on limited survey information. Following further baseline surveys and the expansion of the natural sett, the ABS was considered too small to be suitable as mitigation and so a second ABS was built in its place in 2021.

These examples show how risks taken can lead to money being spent on mitigation which either was not required or not suitable. However, the implications of not being able to close the existing setts on time, delaying the programme of a major infrastructure project, would have been much more costly than the precautionary design and build of the ABS.

Flooding and drainage

Although the location and ABS design included consideration of likely flooding (i.e. not being within a flood risk zone or within an area known to retain standing water), two of the ABS constructed in 2020 were subsequently found to have flooding issues. These had to be destroyed and replaced in 2021. The local flooding issues would not have shown up on checks of data such as flood risk zones and the land was not in HS2 possession leading up to the ABS build, so previous seasonal and local water levels were not known.

One of these ABS, which had evidence of badger use in 2021 and 2022 was subsequently found to be close to standing water in 2023 following heavy winter rains and nearby construction works which appeared to have temporarily affected local land drainage.

To reduce the risk of waterlogging on Phase 2a the indicative ABS design included setts in naturally raised ground or in created bunds, with granular fill material at the base to aid drainage and a minimum of 150mm above floodwater level for the area. Each nesting chamber was also designed with a foundation of free draining mineral aggregate, 250mm thick, to enable quicker drainage.

Design and construction

Having a practical ecologist with abundant field experience, overseeing the construction of the setts is essential. ABS design is difficult to capture in a technical drawing, which relies on being able to provide a fixed layout and dimensions. There needs to be flexibility on site to tweak the design, based on the local conditions and environment. However, there will be limits to this flexibility due to land access and the presence of constraints such as utilities, land boundaries, tree roots and in some cases planning limits. Therefore, the design should include a potential geographic area within which the ABS could be located which is larger than the ABS dimensions to allow for slight amendments during the build.

Tunnel size

Some of the ecologists involved in the design of ABS were concerned in several locations about access to badger setts from dogs, where these were near publicly accessible areas. A guidance note^[6] published on-line by Nature Scot (formerly known as Scottish Natural Heritage, the public body responsible for Scotland’s natural heritage) regarding ABS construction recommends tunnels are constructed from 12″ (300mm) diameter pipes throughout but reduced at entrances to 9″ (225mm) pipes, restricting the size of any dog that could enter the sett, but allowing badgers easy access. The available badger guidance on CIEEM’s good practice guide for badger does not have any drawings or text referring to ABS design. A previously published book did contain specifications for badger sett design, but this is now out of print^[7].

Natural England’s Wildlife Licensing Service have since confirmed that the guidance offered by Nature Scot is not relevant to Natural England licenses and tunnel diameter throughout ABS should be 300mm diameter.

Entrance tunnels can be installed with bends, to avoid issues with prevailing winds making the tunnels and chambers draughty. Introducing bends may also discourage dogs and other non-target animals accessing the ABS.

Sustainable design

In 2020, HS2 Contractors trialled six ABS using more sustainable materials within the design. Rather than HDPE (plastic) piping for tunnels for setts they used strengthened recycled cardboard (fibreboard). The Contractors worked with a manufacturer on the design and trialled the six ABS with mixed results. Further detail is provided in the accompanying case study (see Sustainable badger sett design case study in supporting materials).

Conclusion

To improve consistency of ABS design across HS2, a technical specification was issued to Contractors which included mandatory requirements, some of which had previously only been issued as guidance (see HS2 artificial badger sett specification in supporting materials). Based on the experience of the design and construction of ABS on HS2 to date, an ABS checklist (see Artificial badger sett design checklist in supporting materials) has also been produced. It is hoped that other projects can use this information to improve mitigation design for badgers.

Acknowledgements

HS2 Ltd wishes to thank the ecologists who were involved in the mitigation, management, and monitoring for badgers under the route-wide licence. In particular, the author would like to thank the following ecologists for comments on a draft of this paper: Caroline Mellor from Wardell Armstrong, Piotr Koryl from Align and Stuart Pankhurst from Southern Ecological Solutions. HS2 also thanks Natural England for comments on a draft of this paper.

References

1. Protection of Badgers Act 1992
2. High Speed 2 (HS2) Wildlife Licensing
3. TB Hub Bio Security Practical Guidance
4. High Speed Rail (London – West Midlands) Act 2017
5. Network Rail (2011) Ecological Works: Artificial Badger Sett Creation – NR NR/CIV/SD/246 ISSUE A. (available from Network Rail on request)
6. Guidance for the Creation of Artificial Setts
7. Cresswell, P., Cresswell, W.J., and Woods, M. (1993) The Country Life Guide to Artificial Badger Setts. Country Life, London. [Out of print]

Supporting materials

• HS2 artificial badger sett design specification
• Artificial badger sett design checklist
• Phase 2a sett design example
• Sustainable badger sett design case study