Acronyms

1. INTRODUCTION

1. This document has been prepared for Berwick Bank Wind Farm Limited (the Applicant) as part of the derogation case for the Proposed Development. The Report to Inform Appropriate Assessment (RIAA) concluded that compensation was required for Black-legged Kittiwake (hereafter Kittiwake) Rissa tridactyla, Common Guillemot (hereafter Guillemot) Uria aalge, Razorbill Alca torda, and Atlantic Puffin (hereafter Puffin) Fratercula arctica (using the worst case ‘Scoping Approach’). These are collectively referred to as the ‘key species’.
2. Compensatory measures for several other species are also identified within this report. These are presented to demonstrate the thoroughness of the compensatory measure selection process undertaken by the Applicant. However, in view of the RIAA’s conclusions the Applicant’s final list of proposed measures only include those targeting the key species.
3. Two colony-based measures are proposed as compensatory measures for the Proposed Development and several others have been explored within this report as part of a thorough compensatory measure identification and selection process. It is proposed that the final measures to take forward are:

• Rat eradication and biosecurity to benefit Kittiwake, Guillemot, Razorbill and Puffin nesting at Handa Island;
• Safeguarding the Dunbar Kittiwake colony through wardening and targeted work to reduce human disturbance and other colony-related pressures;
  4. Background information on how the colony-based compensatory measures were identified and prioritised is detailed in full within the main derogation case for Berwick Bank offshore wind farm.
  5. This report provides technical detail on each of the colony-based compensatory measures that were taken forward for further consideration and discussion with regulators and Statutory Nature Conservation Bodies (SNCBs) as part of the Applicant’s Seabird Compensation Consultation process.
  6. The feedback given in response to these consultation meetings was used to prioritise the ‘long list’ of potential compensatory measures, and at the end of this process the measures were divided into three Tiers, which are defined as follows:

• Tier I: Measures that are agreed to be beneficial, were generally viewed positively, and which can be implemented within the short term
• Tier II: Measures that are agreed to be beneficial, but which are difficult to quantify, or which would require a further data-gathering stage prior to implementation.
• Tier III: Measures which were discussed as a part of the consultation process, but which were not progressed due to lack of support from SNCBs and/or regulators, but which may still have the potential to deliver some compensation benefit.
  7. Tier I measures are implementable. Tier II measures are not currently being progressed but are considered to be beneficial and of potential value as compensation. Tier III measures may be able to provide some compensation benefit but in general have greater difficulties associated with them and have therefore not been progressed (Table 2.1).
  8. The specific aims of this report are to:
• Demonstrate the range of potential compensatory measures considered and discussed with regulators and SNCBs;
• Provide detail of the evidence base behind each of the potential colony-based compensatory measures;
• Provide information regarding the anticipated compensation benefits, quantifying these wherever possible based on the best available data.
  9. The evidence base differs for each of the potential compensatory measures. Various types of evidence are presented and discussed that relate to each potential compensatory measure. Information sources include, but are not limited to, scientific studies, site-specific data, historical information, warden’s reports, consultation with experts, and the results of bespoke fieldwork. In each case the potential benefits to both target and non-target species are described. Sources of uncertainty are discussed. Although all the compensatory measures included within this report are without exception additional to current colony management, a section on additionality is included to demonstrate this.
  10. A brief description of the project and the mechanism for delivery are included to provide a coherent description of how each measure would work. Further detail regarding implementation and monitoring for each of the Tier I measures is provided in full within the Implementation and Monitoring Plan.
  11. The compensation benefits of the Tier I measures have been quantified using available evidence from a range of sources, which are documented for each measure. Compensation benefits are presented in terms of conservation targets acknowledging that what is predicted may not necessarily be achieved due to the various uncontrollable factors that may potentially impact on wild bird populations (e.g. disease outbreaks, storms, marine heatwaves and other force majeure events). However, in each instance the evidence base is used to generate an estimate of what level of benefit is considered likely on the basis of evidence to be achievable.
  12. It was not possible to quantify potential compensation benefits for all the Tier II and III measures and therefore this information is only included where sufficient evidence was available for reasonable estimates to be provided.
      

Table 1.1: Colony-based compensatory measures and their prioritisation ranking.

2. TIER I: RODENT ERADICATION FROM ISLANDS

2.1. BACKGROUND

13. Invasive non-native species (INNS) of relevance to seabirds covers a wide range of flora and fauna. Invasive Tree Mallow Malva arborea for example, forms a dense canopy and may displace native vegetation and prevent burrow occupancy by Puffin on some Firth of Forth islands. Moreover, while a range of introduced mammals such as European Rabbit Oryctolagus cuniculus may have a range of indirect ecological effects on seabirds, it is the predatory species that are seen to be the major threat. In the UK, these may include Black Rat Rattus rattus, Brown Rat Rattus norvegicus, Feral Ferret Mustela furo, Feral Cat Felis catus and American Mink Neovison vison. Other native predators such as Stoat Mustela erminea or Red Fox Vulpes vulpes that are not resident but may occasionally colonise islands may also be treated as INNS in this context. Feral Cat, Red Fox and the mustelids predate adult seabirds as well as chicks, with eggs also taken by all but the former species. Rats are seen to be a particular problem for eggs and young chicks, with House Mouse Mus musculus also taking a predatory role in particular circumstances. 
14. Eradication of INNS from islands has become a focus in the UK following its success in other locations around the world and its role in reducing extinction risk of a number of species including Seychelles Magpie-robin Copsychus sechellarum, Cook’s Petrel Pterodroma cookii and Black-vented Shearwater Puffinus opisthomelas is now widely acknowledged. In the UK, rodent eradication has been particularly successful at improving the breeding success of burrow (and crevice) nesting species such as Manx Shearwater Puffinus puffinus, European Storm-petrel Hydrobates pelagicus and Puffin (Thomas et al. 2017a). Such is the pervasive effect of rodents that their eradication has been termed ‘Island Restoration’ (Thomas et al. 2017a); although, as this may imply restoration of the whole island ecosystem, rather than just the removal of alien invasive species in order to benefit seabirds, this term is not used here.
15. The eradication of rodents, from islands was raised and actively recommended by some stakeholders during consultation. Eradication of rodents from islands has the potential to be more successful than removal from mainland seabird colonies where re-colonisation is inevitable, and a rodent-free status cannot feasibly be maintained. By contrast, if eradication from islands is accompanied by effective biosecurity measures, safe nesting habitat for seabirds can result. There are three basic components to a successful campaign; 1) confirmation of presence and the potential scale of the issue, 2) attempted eradication, and 3) the implementation of a biosecurity plan to avoid re-incursions, monitor for re-incursions and to deal with any re-incursions that do occur.
16. Flavoured wax blocks that are attractive to rodents are typically deployed to monitor for their presence. This technique shows which areas the rodents may be occupying and will provide some index of abundance. Poison is not used for surveillance purposes due to the risks posed to non-target species (through either primary or secondary poisoning), especially where no rodents are ultimately found. Other surveillance methods include tracking tunnels, cameras and the use of traps, particularly low-maintenance self-setting traps that are deployed for relatively long periods and record the number of target animals killed.
17. The eradication phase by contrast typically requires the use of rodenticide, although other methods such as A24 traps, which use a specially designed lure, are under trial. The rodenticide is typically placed around the island by positioning bait stations at intervals in a grid formation. To ensure that all rodents are removed it may be necessary to install rope access routes across cliff faces. The eradication phase is carried out in the winter when rodent numbers are naturally at their lowest, and when natural food supplies are low. This means that there are fewer rodents to catch, and those that do remain are more likely to take the bait in the absence of other food sources. The winter period also avoids any risk of harm to breeding birds, although it does mean that islands have to be accessed during challenging weather conditions.
18. Alongside the initial intensive eradication phase, biosecurity measures need to be put in place to ensure the hopefully acquired rodent-free status is maintained. Biosecurity planning involves the identification of risk species and potential ‘pathways’, such as boats, helicopters, visitors, lighthouse boards and construction work. Prevention measures are required to ensure that invasive species are not transported via these potential pathways.
19. Surveillance continues thereafter, potentially using the same or similar methods to that deployed at the start of the project. It is essential to have an incursion response plan that comes into force should the reoccurrence of rodents be detected. The quicker the response, the easier it is likely to be to initiate further removal and for this to be successful as only a few animals may be involved (Thomas & Varnham 2016). Incursions can and do happen regularly (T. Chuchyard, Director RSPB Biosecurity Project, pers. comm).
20. In the UK, the EU Biosecurity for LIFE Project is underway and aims to eliminate INNS from the 42 islands in the UK that are designated as SPAs by carrying out monitoring to detect INNS and putting biosecurity measures in place to ensure they remain free of invasive species. A number of islands within the Forth Islands SPA form a part of this project, which is funded through a grant that will finish in July 2023. These islands are: Bass Rock, Isle of May, Fidra, Lamb, Craigleith and Inchmickery
21. Although the Forth Islands that form part of the Forth Islands SPA are free of rats, it was suggested that the Applicant could investigate and undertake alien invasive species removal and biosecurity at non-SPA islands supporting the key species. This is a compensatory measure that was recommended to the Applicant by the RSPB (A. Dodds RSPB, pers. comm[1].).

2.2. ISLAND SELECTION PROCESS

22. SSER undertook a review of the non-SPA Forth Islands (see Table A1 in Appendices), which showed two islands where rodent eradication could be undertaken to benefit small breeding colonies of the key species. Landowner and community support is crucial for rodent eradication projects, and of these islands only Inchcolm Island supported colonies of the key species and promising levels of stakeholder support required for rat eradication to be successful. Since Inchcolm is not an SPA, eradication of rats and implementation of biosecurity control measures at this site would not otherwise be undertaken.
23. During stakeholder consultation Handa SPA was identified as a potential site for compensation. Although Handa is currently participating in a trial to assess the efficiency of self-resetting A24 traps in a control context around seabird colonies, there is currently no concerted effort underway to eradicate rats from Handa. This work has been undertaken under the EU Biosecurity for LIFE Project, and will end in 2023. The success of the A24 traps is in question, as there are still significant numbers of rats on Handa and at present there is no source of available funding to eradicate them (R. Potter, NE Reserves Manager SWT, pers. comm).
24. Handa is designated as an SPA and at the time of designation in 1990 supported populations of European importance for Guillemot (98,686 individuals – 9.3% of the British population and 2.9% of the North Atlantic biogeographic population) and Razorbill (16,394 individuals – 11% of the British population and 1.9% of the Alca torda islandica population). It also supports nationally important colonies of Kittiwake (10,732 pairs, 2.2% of the British population), as well as several hundred Puffins (735 AOB). The most recent counts show there are an estimated 68,524 Guillemots (individuals), 3,749 Kittiwakes (AON), and 5,047 Razorbills (individuals). On the basis that Handa supports national and internationally important colonies of the key species that require compensation from Berwick Bank, it was considered as a suitable island for compensation.
25. Concerns were raised following the Applicant’s Compensation Consultation meeting held on 30th March 2022[2] regarding the distance of Handa from the Proposed Development, and the requirement to systematically look at compensation at closer sites before moving onto more distant sites within the SPA network. To address this concern, a systematic search work was carried out to ascertain whether other closer and/or potentially more suitable islands could be identified and potentially investigated.
26. The RSPB Islands Database[3] was used to search for all other islands along the east coast of the UK. This dataset was overlain with the Seabird Nesting Counts shapefiles produced by the JNCC[4] to identify islands where the key species were known to be nesting. The aim was to identify any islands supporting breeding colonies of the key species closer to Berwick Bank, which had not previously been identified or considered. Islands from the east coast of the UK were selected as a priority group for examination as it is anticipated that connectivity to the main SPAs would be greater.
27. Although there are ~9,000 islands in the UK, only a few (111 in total) are on the east coast, creating a smaller sub-set for further examination. Overlay of JNCC Seabird Nesting Counts data for the key species revealed that only 19 islands on the east coast supported breeding colonies of the key species (see Table A2 in Appendix).
28. Once these islands were identified, they were classified according to their suitability for rat eradication. Islands were not considered suitable if they met any of the following criteria:

• They have never supported rats – some islands are naturally rat free as they do not have the habitat to support rats and/or are too far from the mainland for rats to reach.
• SPA islands that have removed/are already removing rats and have biosecurity plans in place.
• Tidally linked islands and/or islands very close to the mainland where risk of incursion is considered prohibitively high.
  29. Of the 19 islands identified, 15 were designated as SPAs were already free of rats and had biosecurity plans in place. There were four islands remaining: Inchkeith, Inchcolm, the rocky outcrops outside of Dunbar Harbour (used by nesting Kittiwakes), and Marsden Rock.
  30. Inchcolm has already been identified as a suitable island for rat eradication. Dunbar has also been identified as a non-SPA Kittiwake colony that could benefit from additional resource (see Section 4). Better control of rodents at the main Dunbar Kittiwake colony has been identified as one of the possible improvements that a full-time site warden could implement.
  31. It is unclear whether there are rodents on Marsden Rock as the cliffs are steep. However, Marsden Rock sits on the beach at low water and would be vulnerable to recolonisation by rats from the mainland, and therefore is not considered a suitable site for rodent eradication.
  32. Since no other suitable islands near the potentially impacted SPAs were identified where landowners supported rat eradication, the search area was widened to encompass the whole of the UK. This was on the basis that there may be closer sites in the north of Scotland that could offer comparable opportunities for compensation.
  33. Whilst Handa has the advantage of supporting large colonies of the key species) it is close to the mainland (only 350m) making it vulnerable to further incursion of rats, which can swim distances of up to 2km. Maintaining islands free from rats is easier if they are uninhabited; there are fewer pathways by which rats can recolonise, and therefore less likelihood of incursions. Handa experiences high numbers of visitors during the summer months (9,000 visitors per year), which is a complicating factor in maintaining Handa free from rats in the long term. It was considered possible that an alternative island could offer similar compensation benefits without these complications.
  34. To explore this the JNCC Nesting Counts data and the RSPB Islands database were used together to identify the top twenty island breeding colonies for each of the key species (see Tables A4-A7 in Appendix). This process was complicated by the structure of the database, which divides the larger islands into several subsites. In the first instance the database was sorted by subsite, and then sense-checked to remove mainland sites. Then counts from all subsites were added together to present counts for whole islands on the basis that this is the most intuitive metric. However, in some instances this was not possible because of the number of subsites and the way in which they had been titled. In most cases the site name took the name of the island, making the process straightforward. However, the larger Scottish Islands (Orkney, Shetland, West Westray, Rousay, Lewis and Skye) were an exception and the main sites were named after cliffs, headlands or other features. Due to the number of sites and subsites on these large islands (hundreds), hand-sorting the counts for each species by island was unrealistic. Furthermore, eradication of rats from these larger islands is considered unfeasible for several reasons: i) sheer cost and scale, ii) the requirement for complete community support (and the inevitable delays this causes in project implementation), and iii) the number of pathways that would need to be controlled to prevent incursion (e.g. regular ferries etc). For these reasons the larger islands named above were removed from the dataset.
  35. It is understood that the islands supporting the largest colonies will be SPAs, and therefore likely either to be free from rodents or with removal underway and biosecurity plans in place. However, this was considered the most useful method of assessing Handa in the context of other similar islands and to see whether other more suitable islands may be identifiable. It was acknowledged that this process may not identify islands supporting smaller non-SPA colonies which may not have any funding resource to remove rodents, such as Inchcolm. However, the aim was to find a larger site to provide a greater level of compensation. Although it can be argued that the same level of compensation may be achieved by tackling a larger number of smaller sites, and that smaller sites are not encompassed by the Biosecurity for LIFE Project, it is clear from the scale of the Kittiwake, Guillemot and Razorbill colonies present on Handa that several hundred smaller islands supporting colonies of a similar scale to Incholm would be required to provide a similar level of compensation as Handa. For example, Handa supports 16,394 Razorbills, whilst Inchcolm only supports 12 Apparently Occupied Sites (AOS).
  36. Once the top twenty islands for each of the key species had been identified, the data was examined to positively identify sites that occurred in the top twenty list for more than one of the key species, essentially generating a list of the most important island colonies for the key species when taken together as a group. The results of this process are summarised in Table 3.1.
  37. A number of islands identified during this process have never supported rats as they are a long way offshore and/or do not support the habitat and resources required to keep rats alive. However, as a part of the Biosecurity for LIFE Project, all SPA islands are being actively monitored to ensure that rats are not transported accidentally (as can and does regularly occur).
  38. Seven islands were identified as supporting large breeding colonies (i.e. those in the top twenty by number) for all four key species. These islands were: Berneray, Fair Isle, Foula, Isle of May, Mingulay, Noss and Skomer. All of these islands are free of rats, although it is notable that both Foula and Fair Isle have feral cats. However, the impact of the feral cats, particularly on cliff on nesting seabirds, is unknown. Furthermore, the eradication of feral cats from inhabited islands is potentially more contentious than the eradication of rats and, as both islands are inhabited, strong community support would be required. However, it is acknowledged that action at these sites could conceivably benefit a greater number of birds of the key species, but equally there is uncertainty as to what level of impact the cats are having. Rats are more likely to access cliff faces than feral cats. Neither Foula nor Fair Isle is much closer to Berwick Bank than Handa so there is no obvious advantage in terms of proximity.
  39. Nine islands were identified as supporting large breeding colonies of three of the key species. Of these islands four did not have rats: Skomer, Colonsay, Farne Isles, Flannan Isles and North Rona. Three islands have had or are in the process of having rats removed. These are Rathlin, Great Saltee and the Shiants. Two islands are known to currently have rats and it is understood that the seabirds nesting there would benefit significantly from their removal. These islands were Handa and Lambay (Ireland). Of these, Handa is both closer and supports larger colonies of the key species and on this basis was considered more likely to deliver a greater compensation benefit. The remaining sites in Table 3.1 support large colonies of only two species.
  40. Although Handa is not one of the major 20 islands which supports Puffin, it does support a small colony of 208 individuals (according to the latest count from SWT carried out in 2021[5]). Inchcolm also has a small Puffin colony (10 birds counted in 2021[6]). It is anticipated that eradication of rats from both islands will enable Puffin to recolonise new habitat. Puffin has undergone significant decline on Handa where it is currently restricted to nesting on Great Stack, which is believed to still be free of rats. On Inchcolm Puffin only nests on the steepest cliffs on the north-west cliffs of the island. Historically Puffins have nested in other areas on both Inchcolm and Handa and could do again if rats were removed. It should be acknowledged that the impacts of rats on burrow-nesting species such as Puffin are likely to be greater than on cliff-nesting species.
  41. Handa has a known rodent problem and monitoring carried out by SWT over the 2021 season shows that rat numbers are still high even after trials with A24 traps were conducted over the winter of 2020 (Rab Potter, Reserves Manager, pers. comm). Landowner cooperation and community support is of critical importance in getting rat removal efforts underway and in the case of Handa, it is of significant benefit that the landowner is supportive of rat eradication. The owner of Handa also owns some of the adjacent land on the mainland, which could potentially be maintained as a rodent free buffer to reduce the risk of further incursion of rats from the mainland.
  42. Further consultation would be needed to ascertain whether there are other SPA sites in a similar position as Handa. However, there does not appear to be any island better suited in terms of compensation for the Proposed Development, either in terms of locality, the match between the species assemblage supported and the key species at the Proposed Development, or in terms of the scale of the rat problem.

Table 2.1: Islands supporting large numbers of more than one of the key species (ranked by the number of key species supported). Abbreviations: RA=Razorbill, KI=Kittiwake, GU=Guillemot, PU=Puffin.

Source:  Bird counts from JNCC Seabird Nesting Counts (British Isles) - data.gov.uk Data on invasive species from: Invasive mammals (cefas.co.uk)

43. Although Handa is not local to the Firth of Forth, it is acceptable to compensate at another site within the same biogeographical region. Seabirds are generally philopatric, however, it is known that some individuals disperse and may not return to their natal colony to breed. For Kittiwake this is thought to be around 15%, with dispersal on occasion covering considerable distances, sometimes involving movements across the North Sea as far away as France, Norway and Sweden (Wernham et al. 2002). On this basis a level of interchange between the east and west coasts of Scotland can be assumed, and therefore removing rats from Handa would constitute compensation in a different, but connected, topographic unit.
44. With regards to the other species, Puffin is the least site-faithful and it is believed that 50% of birds will breed away from their natal colony (Wernham et al. 2002). Over the course of a breeding season second- and third-year Puffins have been observed visiting several different colonies sometimes hundreds of km apart, presumably assessing their potential as future breeding sites. On this basis it seems likely that birds from Handa would end up breeding on the east coast of Scotland.
45. Guillemot and Razorbill are believed to be highly philopatric, with a Canadian study showing that 83% of young Razorbills and 93% of adult Razorbills returned to the same colony to breed (Lavers et al. 2007). However, even Razorbills can disperse over long distances: a chick ringed on Handa in 1971 was seen four times at the Gannet Islands some 3,219 km away (Lavers et al 2007). Like Puffin, young non-breeding Guillemots will often visit breeding colonies, presumably with a view to returning there later to breed. For example, on the Isle of May, 51 young Guillemots were observed that originated from other UK and Irish colonies (Wernham et al. 2002). Another study from the Isle of May suggests that 25% of Guillemots reared there may have bred elsewhere (Harris et al. 1996). Therefore, some level of connectivity between Handa and colonies on the east coast of Scotland may be reasonably demonstrated for all the key species.
46. On this basis implementing compensation at Handa would fulfil the requirement for the project to provide suitable compensatory measures to secure the overall coherence of the national site network.
    

2.3. INCHCOLM: RAT ERADICATION, BIOSECURITY & COLONY MANAGEMENT

2.3.1.    Site description

47. Inchcolm measures 9 ha in size, reaches 34m at its highest point, and is located only 1 km from the mainland. The island is comprised of two segments (eastern and western), which are linked by a narrow isthmus, at one time covered by the incoming tide, but which has long been built up to form a permanent causeway. The eastern part of the island is hilly rising to approximately 30m above sea level. The western part is somewhat flatter, but gently rises to a similar height at its western extremity where stretches of cliffs can be found. The island is famous for its ancient Abbey and its World War 1 and 2 military fortifications. It has some small sand beaches, but otherwise it is rocky. The grounds of the Abbey and the tourist reception area are landscaped comprising mowed grass, ornamental shrubs and hard standing. The rest of the island is largely dominated by coastal grassland vegetation with small shrubs and trees
48. The island is regularly visited by tourist trips to Inchcolm Abbey during the summer months, with up to four employees of Historic Environment Scotland (HES) living on the island during the summer to staff the abbey and shop. The abbey may also be hired as a wedding venue. Inchcolm has no nature conservation designations and no history of management for seabirds. The island is part of the Moray Estate, although HES have responsibility for running and maintaining the abbey.
49. Situated within 500m of Inchcolm island there are the two small barren rocky islets of Carr Craig (to the east) and Haystack (to the west) both of which have been important breeding grounds for several species of tern in the past, and in more recent years have hosted important colonies of Great Cormorant and European Shag.
50. Inchcolm is known to support a colony of Black Rats. Consequently, it was a surprise when the Forth Seabird Group discovered a Kittiwake colony there in 1991, as it was thought that the rats would discourage nesting seabirds (ENHS Report 1992). Further information on Black rat and the impacts of Black rat on seabird populations is included within the feasibility study (Cain et al., 2022).
51. The seabirds nesting on Inchcolm were counted annually by the Forth Seabird Group and are now counted annually by the Forth Islands Heritage Group (FIHG). Only very small numbers nest there with the colony in 2021 numbering 63 AON for Kittiwake, 12 AOS for Razorbill, and 10 Puffins (single birds). Guillemots have been observed on Inchcolm on several occasions (single birds in 2007 and 2008, and 14 individuals in 2014) and it was speculated that a very small number may breed there. However, they have not been sighted on more recent surveys (2015–2021). The number of birds present on Inchcolm is extremely low both relative to other unmanaged non-SPA islands such as Inchkeith and relative to the other rodent-free Forth Islands that are included within the SPA designation, and it is speculated that this could be due to the presence of Black Rat, which is considered to be even more detrimental than Brown Rat as a result of its greater agility and ability to access remote nesting locations.
52. Kittiwake numbers on Inchcolm remained relatively stable during the period between 2004–2008 (Figure 2.1) when numbers declined rapidly elsewhere (see Figure 3.1 in Section 3.2.4 for comparison). However, numbers then dropped further between 2014-2018, when numbers have stabilised or even increased elsewhere. The period of relative stability during the mid-noughties (when other sites declined) may be attributable to dietary differences, with Kittiwakes in the Inner Forth (Inchkeith and Inchcolm) taking a higher proportion of clupeids rather than sandeels (Bull et al. 2004). However, it is not clear why numbers declined between 2014-2018 in recent years when they did not elsewhere. Comparison with Inchkeith, another non-SPA site in the Inner Forth, shows that Kittiwake numbers were generally stable between 1996-2014 (unlike other sites in the Forth Islands) with numbers increasing post-2014. It is considered likely that the presence of Black Rat on Inchcolm could be an influential factor in the recent decline of Kittiwake.
53. Although Razorbill numbers have risen slightly over the last decade, the colony is still only very small relative to rodent-free islands in the Forth (see Section 2.3.5). Puffin counts are variable, but in recent years are always below 60 individuals, numbering only 10 individuals in 2021 (Forth Islands Heritage Group 2021). However, 28 Puffins were seen by the Forth Island Heritage Group off the north-west cliffs of Inchcolm on 20th July, which is considered to be a more representative number of the population than the official count carried out on 31st May (Forth Islands Heritage Group 2021).

Figure 2.1: Counts of Kittiwake, Puffin, Razorbill and Guillemot taken at Inchcolm (data source Forth Seabird Group website: http://www.forthseabirdgroup.org.uk/index.htm, Forth Island Heritage Group reports 2020 & 2021)

54. Anecdotal evidence suggests that numbers of Puffin were previously much higher on Inchcolm with peak numbers between 1992-1995 reaching 100 pairs. In the 1990s the Puffins used to nest in a boulder field in the south-eastern corner of Inchcolm, but now they are restricted to the steeper cliffs on the north-west of the island, where there are now only a few pairs (R. Morris, FIHG pers. comm). It is thought likely that they are confined to the cliffs because of Black Rat. However, even though the few remaining Puffins are nesting in the least accessible part of Inchcolm, Black Rat can still reach them even here (see Section 2.3.3). Although Guillemot does not currently breed on Inchcolm, it is also anticipated that rat eradication would increase the value of the habitat and improve colonisation potential.
55. However, the number of large gulls (primarily Lesser Black-backed Gull and Herring Gull) nesting on Inchcolm will also affect auk populations through predation of chicks. The vegetation and ground cover means that conducting accurate counts is challenging, so in 2021 the Forth Islands Heritage Group conducted a large gull census on Inchcolm, which showed that numbers were much higher than previously anticipated with 1641-1789 Lesser Black-backed Gull AOT, 1694-1847 Herring Gull AOT and 7 Great Black-backed Gull AOT. Large gulls were observed nesting in the grounds of the Abbey for the first time due to lack of visitors and maintenance during the 2020 closure due to COVID-19 pandemic lockdown.
56. However, any solutions even involving non-lethal control of gulls were not popular with stakeholders (see Section 7.2), who as a general principle did not want to see one species favoured over another (meeting held 8th February 2022). Although maintaining specific areas as ‘gull free’ is standard management practice at other sites, such as the Isle of May, which also supports large numbers of Herring Gulls, this approach is not discussed further beyond briefly flagging its potential value at a non-designated unmanaged site like Inchcolm to aid recovery of auk populations, which are currently very low and therefore potentially vulnerable.
57. It is acknowledged that maintaining biosecurity at Inchcolm would be challenging because of the number of visitors to Inchcolm Abbey, and its proximity to the mainland, which means that it is at high risk of colonisation by Brown Rat. However, rodent eradication and biosecurity have been successfully carried out in more challenging locations such as St Agnes and Gugh on the Scilly Isles, which are inhabited. The risk of recolonisation can be minimised through regular surveillance, although the time and effort required to achieve and maintain rodent free status at Inchcolm should not be underestimated.
58. Following identification of Inchcolm as a potential island that could benefit from rodent removal, a full feasibility study was commissioned (Cain et al., 2022) of which a summary is provided within this document.
59. The feasibility study included: i) a field study (rodent trapping), ii) a nesting habitat assessment, iii) a seabird colony census, and iv) a desk study looking at the assessment of 7 key feasibility criteria described in the UK Rodent Eradication Best Practice Toolkit (Thomas et al. 2017). These are technical feasibility, sustainability, social acceptability, political and legal acceptability, environmental acceptability, capacity and costs.
60. The feasibility report concluded that a well-planned eradication programme managed by experienced operators, adequately funded, and supported by the landowner and stakeholders, would result in the eradication of Black Rats from Inchcolm and would improve the habitat for target seabirds[9] to breed more successfully and for colonies to expand.
61. Although four of the seven key feasibility criteria were met, further consultation was recommended in relation to three areas: sustainability (that is the required commitment to maintain a comprehensive biosecurity plan), political and legal acceptability, and social acceptability.
62. Consultation with a range of local stakeholders was conducted during July and August 2022. The consultation was generally positive with the majority in favour of rat removal. HES have indicated that further stakeholder consultation would be required before this specific measure could be secured, the intention is not to take this measure forward as compensation at this stage. Instead, this measure is being presented as a secondary measure that could be implemented as an adaptive management measure if required post consent.

2.3.2.    Field survey of mammalian predators

63. A field study was carried out by NBC Environment (working in collaboration with WMIL) to assess the abundance and species of invasive mammalian predators present on Inchcolm. Five nights of trapping was undertaken between 13th-23rd June 2022. A total of 80 traps, 9 cameras, 10 ink tunnels, 10 wax blocks and 6 mice boxes were deployed across Inchcolm (Figure 2.2). A range of survey techniques were employed as this approach has been shown to improve the detection of rats. The survey adopts the methodologies described in the UK Rodent Eradication Best Practice Toolkit (UK Biosecurity for Life) (Thomas et al. 2017). Full details of this work are included in the feasibility study (Cain et al., 2022).
64. A total of 29 Black Rats were caught over the five nights of trapping and appeared to be distributed across the island (Figure 2.2). No other mammalian predators were detected. All rats caught in kill traps were necropsied and tissue samples were dispatched to laboratories for DNA analysis including genetic sequencing, rodenticide resistance testing and stable isotope analysis to ascertain the food types contributing to rat diet. Initial examination of stomach contents indicated the presence of egg-shell in at least one sample. Stable isotope analysis of whiskers taken from a sample of the Inchcolm rats showed the rat’s diet comprised a marine high trophic level signature, which could be indicative of seabird predation. However, without taking samples of the target seabirds, this test was unable to differentiate between a seabird food source and another high trophic source, for example a dead seal.
65. Abundance (or rat density) is recognised as low (less than 10%), moderate (between 11-25%), high (between 26-50%) and very high over 50% (Moors 1985, King & Forsyth, 2021). The index of rat abundance for Inchcolm was 8 rats per 100 trap nights. This suggests a low rat abundance across the island, but this result may be complicated by the trapping time (summer, June 2022) and the abundance of natural food reducing trapping efficacy. This possibility is confirmed when the trapping results are compared to the index from the tracking tunnels (27 active tunnels per 100 trap nights). This suggests that black rat numbers are moderate to high on Inchcolm ((Cain et al., 2022).
66. The DNA analytical results show there were no rodenticide resistance genotypes in the black rats trapped on Inchcolm. This suggests that rats could be controlled/eradicated using first generation or second-generation anticoagulant rodenticides (FGARs or SGARs). Rodenticides such as coumatetralyl or bromadiolone could be used to control/eradicate these populations rather than utilising the more toxic brodifacoum or flocoumafen required for resistant populations.

Figure 2.2: Locations of monitoring equipment deployed on Inchcolm between 13th-23rd June 2022. Red marks show locations where rats were detected.