4. TIER I: REDUCTION OF THE GANNET HARVEST AT SULA SGEIR

4.1. Background

  1. The Gannet population in the UK has risen by 34% between surveys carried out in 1969/70 and in 2013–15 (JNCC 2021). This increase is attributed to the cessation of hunting[32] dating from the end of the 19th century (Nelson 2002). However, Gannet is classified as being of ‘Amber’ conservation concern because the UK contains an internationally important breeding population (at least 20% of the European population) and has at least 50% of breeding birds present in 10 or fewer colonies (Eaton et al. 2015).
  2. Bass Rock supports the largest UK colony and is also the largest gannetry in the world supporting 14.3% of the world population (Murray et al. 2014). The population numbered just 8,077 pairs in 1968 and increased by 832% to reach 75,259 pairs in 2014. The rate of increase at 4.4.% per annum (from 2003/4) has been higher at Bass Rock than is typical at around 2% per year (JNCC 2021).  
  3. All Gannet SPA breeding populations are in Favourable conservation status which is in marked contrast to the situation for many other seabird populations (Murray et al. 2014). The Outer Firth of Forth and St Andrews Bay Complex SPA was recently classified (December 2020) with breeding Gannet as a breeding season feature (as was The Seas off St Kilda SPA), which effectively recognises the area as of importance for foraging Gannet, mainly originating from Bass Rock. No offshore sites were listed as being designated for non-breeding Gannet in the 3rd UKSPA review (Stroud et al. 2016).
  4. Gannet productivity has been stable over time (JNCC 2021) suggesting that the population is generally not limited by prey shortages due to their adaptability and ability to forage over great distances (typically up to 700 km) from their nest (Hamer et al. 2000). This conclusion also logically accords to steadily increasing populations in the UK. However, extended foraging range is also a response to reduced prey availability perhaps as a result of intense competition for resource around large colonies in particular. Thus, Gannets from Bass Rock travel as far as the Bergen/Viking Bank near the Norwegian coast to find food, a round trip of up to 1,291 km (Hamer et al. 2007). Usually, one parent will stay with a chick whilst the other forages, though if left for long enough it will eventually leave to find food. This leaves the chick vulnerable to attack, mainly from other Gannets seeking prime nesting space. Impacts upon breeding success are anticipated if reduced prey availability promote any further increases in trip duration or foraging effort.
  5. Fisheries-based measures to reduce or remove sandeel fishing pressure in SA4 will be of benefit to Gannet, as they forage on sandeels as well as larger fish such as Atlantic Mackerel Scomber scombrus, gadoids and clupeids. A study of 266 regurgitate samples from Gannets at Bass Rock showed that the main prey items in terms of frequency of occurrence were Mackerel, sandeels (mainly 0-group), Sprat and Herring. In terms of biomass, sandeel accounted for 17.9% of diet (Hamer et al. 2000). Fisheries Compensatory Measures (FCM) are discussed in a separate FCM Report submitted alongside this document.
  6. The possibility of compensating for Gannet within the area in proximity to the Proposed Development was assessed in ECON & ABPmer (2021a). Although Gannets are not limited by prey, they are limited by habitat availability at Bass Rock as the colony is virtually at full capacity. Under these conditions, it is likely that many chicks (perhaps even several thousand per year) will be lost falling from cliffs due to competition for space with other Gannets. A 3-year study at Ailsa Craig, a colony where, unusually, any falling gannets can be retrieved from scree underneath the cliffs, recorded between 445–461 dead or injured gannet chicks over the course of a breeding season, accounting for about 6% of the chicks hatched (Wanless 1983). The author postulates that this number may be reduced at sites where birds fall into the sea, as some fledged birds may survive the fall. However, even taking this into account the losses are likely to be substantial. The possibility of establishing another gannetry was discussed with stakeholders but was felt to be problematic due to lack of other suitable nesting cliffs within the Forth coupled with the natural expansion of birds into St Abbs NNR, where a few pairs have started nesting on one of the stacks in recent years.
  7. Reducing the impacts of predation and human disturbance on Gannet were also considered. Whilst a few Great Black-backed Gulls are known to take Gannet eggs at Bass Rock, the size of the gannetry is such that this is not a significant problem. However, at other sites such Sule Skerry, which in 2003 was a start-up colony of 15 nests, 30% of nests were predated by Great Black-backed Gull. However, even under these relatively difficult conditions this colony continued to increase year on year and by 2015 held 1,870 nests (Mavor et al. 2004). Since most gannetries are in remote locations, often on inaccessible cliff faces, Gannets were in general felt to be less impacted by human disturbance than other species. Although individual nests at Bass Rock near the path may be disturbed by visitors, the benefits of limiting disturbance are considered likely to be minor.
  8. Measures to reduce bycatch of Gannet were also evaluated. In summary, Gannet has been identified as one of the seabird species most at risk of bycatch during the breeding season and in the inshore waters of Scotland (Bradbury et al. 2017), with most of the deaths attributable to offshore static net fisheries and longline fisheries (Northridge et al. 2020). In the Forth and Tay area specifically, there is no evidence of significant long-line and gillnet fishing effort that may be impacting local breeding birds. Where longlining does take place it is mainly a more artisanal fishery using feathers rather than baited hooks. Furthermore, the UK Plan of Action on Seabird Bycatch is already collaborating with multiple stakeholders to identify priority measures to reduce or eliminate incidental bycatch. This may translate into feasible pathways that could constitute compensation for wind farm development in the future.
  9. There is also considerable albeit largely unquantified bycatch of Gannet when overwintering along the Atlantic Iberian coast including Portugal (Oliveira et al. 2015, Calado et al. 2020) and into West Africa (Grémillet et al. 2015, 2020). Gannet is taken especially by longlines, including in artisanal fisheries but also in purse-seines, and generally appears to the most frequent seabird captured. Bycatch has led to a precipitous decline in the number of tagged birds returning to a colony in Brittany, northern France (Grémillet et al. 2020). Losses to fisheries will also invariably affect UK SPA populations although the scale of the impact is currently unknown. As a result, the benefit of implementing measures to reduce bycatch of wintering birds to benefit UK SPAs cannot currently be quantified. Implementation would also require significant international cooperation and seems likely to be extremely difficult.
  10. By contrast, human predation, in the form of the traditional licenced summer harvest of Gannet at Sula Sgeir results in up to 2,000 fully-grown chicks (known as guga) taken annually. Reported numbers are also close to this limit, with an average of 1,917 taken per year from 2004 to 2014 (Trinder 2016). The disturbance to the whole colony during this process is also significant. Although simple population modelling indicates that the harvest is sustainable, the harvest has reduced the rate of population growth at Sula Sgeir relative to other colonies (Trinder 2016). It also may be the case that harvest affects the growth rate of other Gannet colonies in the region due to natal emigration between colonies. The Sula Sgeir population may therefore act as a sink for emigrant Gannets from other colonies and ending the hunt could lead to increased growth of the surrounding colonies.
  11. For this reason, reduction of the annual Gannet hunt has been identified as being the most feasible mechanism to compensate for potential losses of Gannet. Due to the highly mobile nature of Gannets, it is anticipated that there would be connectivity between the Bass Rock population (located in proximity to the Proposed Development) and the Sula Sgier colony. Even though, like most seabirds, the majority of Gannets are thought to return to their natal colony to breed, there is evidence that some birds move between colonies as shown by a chick from Eldey (Iceland) that was subsequently found breeding on Bass Rock (Wernham et al. 2002).

4.2. The Annual Gannet Harvest

  1. Historically, the eggs and chicks of a number of seabird species would have been eaten for subsistence by local communities within Scotland, Ireland and the north of England. The annual harvest of Gannet chicks from Sula Sgeir (part of the North Rona and Sula Sgeir SPA) is carried out by a few individuals of the Isle of Lewis some ~65 km to the south and is a traditional practice of significance to cultural heritage mirroring similar seabird harvests elsewhere, such as the Gannet harvest undertaken annually at Mykines in the Faroe Islands. Seabird harvests also continue in other northern nations such as Iceland, Greenland and Norway.
  2. The annual guga harvest is the only remaining licenced seabird harvest in the UK. Other subsistence hunting of seabirds came to an end in 1954 when the Protection of Birds Act was passed, which banned the killing of seabirds across the whole of the UK. An exception was made to enable 10 men from the village of Ness (on the Isle of Lewis) to apply for permits to cull 2,000 guga annually from Sula Sgeir.
  3. The harvest involves 10 men from Ness undertaking a long and treacherous journey to Sula Sgeir, which was traditionally carried out on a rowing boat, but now is undertaken on a chartered fishing boat. The Gannet chicks are harvested during the 2-week window before fledging, as they are only considered to be good to eat if taken during this period. On return to Lewis, guga can only be purchased directly from the crew.  
  4. The harvest itself is believed to date from the 16th century, and the men carrying out the harvest today still use more or less the same methods and keep the same traditions. Also, each man has a cairn and places a stone there for each year that they undertake the harvest. On their last visit they place a stone cap on the cairn (Day 2010).
  5. Historically, Gannet would have been an everyday food item for the men of Ness, particularly over the winter period when fishing was dangerous. Although the passage to Sula Sgeir is treacherous and climbing down the cliffs would have been highly dangerous, fewer men died during the guga hunt than they did fishing. The guga harvest was also considered more reliable than crofting, as crops could fail or suffer blight leaving the community short of food (Murray 2015).
  6. It used to be that only native men from Ness who could speak Gaelic were allowed to go on the guga hunt, but rules have relaxed since there are so few young people that speak Gaelic. In fact, the population of Ness has halved in the past 50 years, with many young people opting to leave the island due to the lack of opportunity and poor pay associated with crofting for a living.
  7. The licence has been gradually reduced from around 3,500 guga to 2,500 and is now set at 2,000. Return rates (supplied by NatureScot) indicate that numbers of chicks taken over the past decade ranges between 1723-2000 (Table 4.1).
Table 4.1:
Numbers of guga harvested 2011-2021.

Table 4.1: Numbers of guga harvested 2011-2021.

Source: Data provided by NatureScot

 

  1. This represents some 17.8% of the single chicks from the 11,230 AON recorded in 2013. It is likely that Sula Sgier acts as a population sink for emigrant Gannets from other UK colonies, which are on average growing at around 2% per annum. With the harvest, the rate of population growth at Sula Sgeir appears to be depressed relative to that recorded at other colonies (Figure 4.1).

4.3. Benefits of reducing the Harvest

  1. Stopping the Gannet harvest is increasingly being viewed as a means of compensation for potential wind farm losses at UK Gannet SPA colonies (MacArthur Green 2021). Wanless et al. (2004) shows that the rate of increase in colony size in relation to breeding numbers in 1969 demonstrates that the rate of growth at Sula Sgeir is far below the expected rate, whereas by contrast Bass Rock lies well above the expected rate (Figure 4.1). Wanless et al. (2004) also point out that in 1969 Sula Sgeir and Bass Rock were of similar size (differing only by 13 AON), but in 2004 Bass Rock contained 5 times as many birds.

Figure 4.1:
Rate of increase of Gannet colony sizes in recent decades in relation to breeding numbers in 1969 (both axes plotted on log scales). The plot shows the colony at Sula Sgeir to be far below the expected rate of population growth compared to other colonies.

Figure 4.1: Rate of increase of Gannet colony sizes in recent decades in relation to breeding numbers in 1969 (both axes plotted on log scales). The plot shows the colony at Sula Sgeir to be far below the expected rate of population growth compared to other colonies.

 

  1. This data supports the hypothesis that Gannet numbers on Sula Sgeir have increased less than at other colonies, indicating that this harvest has apparently affected the rate of colony growth. The harvest of 2,000 chicks per year also probably affects productivity of unharvested nests through the human disturbance involved. Significantly reducing the harvest is considered highly likely to result in the growth of the colony and other colonies in the northeast Atlantic metapopulation of Gannet.
  2. Halving the quota to 1000 gannets would result in the addition of 258 adult birds to the population (based on the mean survival rates presented in Horswill & Robinson 2015). The impact of adding these birds to the population would need to be modelled to fully demonstrate the benefit that halving the quota would have. However, this calculation demonstrates that in principle this scale of reduction would compensate for the modelled impacts of the Proposed Development.

4.4. Timescale & mechanism for delivery

  1. The principle for implementing this measure would be based around offering a compensation payment to the guga hunters in return for them reducing their quota. This would not necessarily require any sort of change to the licence and could therefore conceptually be implemented relatively rapidly.
  2. If a change to the licence is required, then this could take longer. However, the licences are issued annually and therefore any delays would still only be of limited duration.

4.5. Additionality & uncertainty

  1. The guga hunt is opposed by a number of animal rights groups that have been campaigning for it to cease. For example, the Scottish Society for the Prevention of Cruelty to Animals (SSPCA) claims that the hunt breaches animal welfare laws.
  2. Opposition to the hunt intensified following Ness Football Club organising a ‘World Guga Eating Championship’ in 2013. One online petition to the hunt reached 70,000 signatures, and in 2017 several of the hunters received death threats.
  3. Whilst there are many that would like to see the hunt stopped, NatureScot (at the time SNH) released a statement saying that they were satisfied that the method used to dispatch the birds is humane and the hunt is sustainable.
  4. At the time of writing, there is no evidence of any action currently underway to stop the hunt, although it has been flagged as a means of compensating for potential losses of Gannets from offshore wind farm developments (MacArthur Green 2021). However, there are no known plans to stop the guga hunt for conservation (or any other) purposes.
  5. Since the harvest is controlled by humans, then there is high degree of certainty that were the current quota were to be halved then the correct number of adult birds would be ‘saved’ to compensate for the potential impacts of Berwick Bank.


5. TIER II: FORTH ISLANDS INCURSION HUB

  1. Section 2.1 describes the background to the EU Biosecurity for LIFE Project. One of the aims of this project is to make biosecurity part of ‘business as usual’ at island SPAs. Previously biosecurity has not been part of routine colony management, although the intention is that by the end of the project biosecurity procedures will be incorporated and carried out routinely (T. Churchyard, RSPB, pers. comm.). However, at present there is no mechanism to fund dealing with re-incursions of invasive species once the EU project comes to an end in July 2023, although the RSPB are in the process of developing incursion response hubs to deal with incursions whilst the project is in operation.
  2. It is hoped that following the end of the EU Biosecurity for LIFE Project that biosecurity procedures will be incorporated into colony management plans (T. Churchyard, pers. comm.). However, once the EU project ends, there is no mechanism to fund the implementation of additional work at SPAs, such as surveillance monitoring to detect potential incursions or funding to dealing with any incursions of invasive species that may occur in future. This problem applies to all SPA sites, the Forth Islands SPA being the closest to Berwick Bank offshore wind farm.
  3. Whilst checking wax blocks for signs of rodent chew marks may be relatively easy for a warden to combine with other routine site visits to carryout bird counts, it is harder for SPA managers to fund the eradication of rats in the event of an incursion as the costs may be significant. This lack of funding is of significant concern as maintaining biosecurity is an essential component of ensuring that the Forth Islands SPA remains in favourable condition in the long term. Re-invasion is a serious issue for several of the key seabird islands, namely Craigleith, Lamb and Fidra, all of which are 1.5 km or less from the mainland and as such are in easy range for Brown Rat, which can swim distances of up to 2 km.
  4. Incursions can and do happen regularly. Since the initial attempt at eradication, rats have already re-colonised Lamb and further eradication effort is again required over the coming winter (T. Churchyard, RSPB, pers. comm.). This island is particularly challenging to monitor regularly as access is difficult, and work is frequently undertaken via a collaboration with a local kayak club. The possibility of the Applicant funding an incursion hub was therefore raised for discussion with stakeholders during the Applicant’s Compensation Consultation process.
  5. It was suggested that the Applicant could supply funding for an incursion response hub which could be used by any of the Forth Islands (including Inchcolm) to deal with incursions of either rats or any other invasive mammalian predators (e.g. stoat, mink etc). An incursion hub would ensure that these islands would remain rodent free in the long term. The impacts of rats on nesting seabirds are described in detail in Section 2 and on this basis keeping seabird islands free from rats is considered an important component of maintaining favourable condition status for the Forth Islands SPA.
  6. Conceptually the project would involve sourcing a staff member and a vessel to be on standby in case of rat incursion. They would then mobilise to deploy traps as soon as they were alerted to an incursion on any of the islands and deploy traps. If this work is carried out rapidly it is easier to remove the rats. If incursion response is slow then the rats will be more widely distributed and difficult to eliminate. If the RSPB incursion hub was up and running the Applicant could supply funding for the hub to continue following the end of the EU Biosecurity for LIFE Project.
  7. Unfortunately, the difficulties in quantifying the compensation benefits meant the incursion hub was not pursued as a compensation option. However, many conservation strategies prioritise maintaining sites that are in favourable condition over tackling sites that are very degraded and this measure is based on similar principles. Many SPAs for seabirds are managed, and without continued management would not stay in favourable condition. However, a measure aimed at maintaining current conditions does not result in any readily quantifiable benefit that can demonstrably offset the potential impacts of the wind farm.

6. TIER II: DIVERSIONARY FEEDING OF SPECIALIST PEREGRINE FALCON NESTS

6.1. Background

  1. Kittiwakes and auks are vulnerable to predation from a range of avian predators including large gulls, raptors and corvids[33]. Eggs, chicks or even adults may be predated, and since seabirds are long-lived, the loss of even a few adults annually can become significant over time. Although predators are an important part of any healthy ecosystem, there are circumstances under which predation may be a cause for concern, and even of colony failure.
  2. Accordingly, although predation was generally considered to not be a significant general factor limiting seabird populations, specialist predators as a distinct and separate issue were discussed on several occasions during stakeholder consultation. Although many large gulls and raptors may consume the chicks of smaller species as a part of their diet, there are some individuals that develop specialisms for seabird chicks and may take little else during the period that the chicks are available. During the course of a breeding season these few individuals may take a surprisingly large number of chicks, which can even have a demonstrable impact on colony productivity (Smart & Amar 2018, Mason et al. 2021).
  3. The removal of a very small number of specialist predators can be a successful means of increasing the population of the prey species. For example, a study at Benidorm Island offshore of the western coast of Spain showed that the selective removal of only 16 Yellow-legged Gulls over the course of 3 years led to a 65% reduction in the number of European Storm-petrels killed. In turn, this subsequently increased survival rate by 16% and breeding success by 23% in the Storm-petrel population (Sanz-Aguillar et al. 2008).
  4. As ethical and environmental concerns over traditional forms of wildlife management increase, there is a trend toward selective management that involves tackling a few ‘problem individuals’. There is strong evidence of individual behaviours in wild animal populations, and there are now a growing number of studies that demonstrate the effectiveness of selective management in providing a mutually acceptable solution (Swan et al. 2017).
  5. However, the issues are complex: many predators themselves are protected species, they are also suffering population declines, and are of equal conservation importance to their prey. Whilst in theory it is possible that removing large gulls from the vicinity of Kittiwake nesting areas would very likely result in significant improvements in breeding success, this would not be palatable to conservation organisations on the basis that Herring Gull (Red) and Great Black-backed Gull[34] (Amber) are of conservation concern in their own right (Eaton et al. 2015, Lopez et al. 2022). 
  6. On this basis, diversionary feeding (DF) was recommended as a means of potentially reducing predation pressure without resulting in adverse impacts on predator populations. DF involves regularly feeding the predator, reducing its need to forage and therefore reducing predation impacts on the prey species. The technique has been successfully used in a number of locations to reduce the impacts of raptors on other protected (or commercially important) avian species. For example, diversionary feeding of a pair of Common Kestrels Falco tinnunculus with white mice reduced the predation rate of Little Tern Sternula albifrons chicks at North Denes (Norfolk) by 88%, resulting in a doubling of Little Tern productivity in the years when diversionary feeding was undertaken (Smart & Amar 2018). Similarly, diversionary feeding of Red Kite Milvus milvus reduced predation of Northern Lapwing Vanellus vanellus, with productivity doubling on average in years when diversionary feeding was undertaken (Mason et al. 2021).
  7. Although DF may be viewed as ‘unnatural’, it is one of the few methods available that allows both predator and prey to successfully raise chicks without harm to either species. DF would only be required for a few weeks whilst the chicks of the prey species are present, allowing the predators to forage naturally for the remainder of the year. It is anticipated that DF would only be used to deal with a small number of specialist pairs or individuals, and on this basis would not be expected to cause an increase in predator populations.
  8. Feedback from NatureScot acknowledged that DF could work for Peregrine Falcon Falco peregrinus (if the nest site is accessible), although they point out that it is unclear how much predation of Kittiwake is due to Peregrines for the Forth sites and indicate that it would be difficult to calculate the level of effect DF might have without further evidence of the current impact of specialist predators.[35]
  9. Peregrines nesting around sea cliffs are known to take seabirds, with some individuals developing specialisms (Sutton & Loram 2021). Although the need to gather site specific data is acknowledged, it is conceptually it is feasible DF of specialist Peregrines to be progressed as a compensatory measure, although this would involve gathering field data during the 2023 breeding season.
  10. Of course, in many instances it may not be feasible to carry out DF: predator nest sites may be inaccessible, or access may entail disturbance of too many other birds nesting nearby, or nests may be too close together for DF to be effective. The objective of this work would be to positively identify situations where DF would be considered to have a high likelihood of success.
  11. The advantage of DF over many of the other suggested compensatory measures is that it involves a direct saving of adults (and/or chicks), as opposed to tackling other indirect factors (e.g. prey, human disturbance etc.) in order to bring about an improvement in productivity. It was suggested that diversionary feeding of other predator species could be trialled, although this suggestion was not popular. However, further information on this topic is presented in Section 7.2. 
  12. Although NatureScot agreed that DF had some merit and acknowledged that it could potentially work successfully for Peregrine Falcon, some issues were raised. DF has not yet been trialled on this species, and it is unclear how much predation of Kittiwake is due to peregrines for the Forth sites. Therefore, a further evidence-gathering stage would be required to identify potentially accessible nest sites and establish what level of benefit DF may have. Since the concept would require further development, it was placed in Tier II as it is not deliverable as a compensatory measure without further investigatory work.

7. TIER III: OTHER MEASURES CONSIDERED

  1. Tier III measures were unpopular with stakeholders and for this reason were not taken forward. The reasons why measures were not progressed are stated in within the summary sections for each measure. They are not being pursued at the current time, as measures that were viewed positively have been progressed in preference.

7.2. Diversionary feeding of other avian specialist predators

  1. The concept of diversionary feeding is described in Section 6 in relation to Peregrine Falcon. Other specialist predators likely to be impacting on auks and Kittiwake in the local area include Great Black-backed Gull, Herring Gull and various corvid species (Carrion Crow Corvus corone, Eurasian Magpie Pica pica, Eurasian Jackdaw Corvus monedula and Common Raven Corvus corax). All of these species may act as specialist predators in some circumstances, although only Great Black-backed Gull would be capable of taking adult Kittiwakes and auks. Corvids primarily take eggs and young chicks. Herring Gulls would take a combination of eggs and chicks of all ages. Predation may be carried out by locally breeding birds or by predators that commute to the colony from elsewhere (see Hario et al. 1994).
  2. A literature review of the main predator species was undertaken (see below) to clarify what is understood about specialist predators and predator-prey relationships affecting the key species both in Firth of Forth area and further afield and to highlight areas where further research could be of benefit in progressing potential compensation though DF.
  3. Although this review focusses on DF, it is acknowledged that other techniques may also be worthy of further investigation, such as the use of canes, which have been successfully used to reduce large gull predation of breeding terns (Babcock & Booth 2020a).

7.2.2.    Great Black-backed Gull

  1. Great Black-backed Gull is the only locally-breeding seabird able to take adult Puffins. They are also capable of eating adult Guillemots and Razorbills, although these are only taken occasionally. Great Black-backed Gulls also take large numbers of juvenile puffins (pufflings), as well as Guillemot, Razorbill and Kittiwake chicks. Some Great Black-backed Gulls are known to wait specifically to catch Puffins as they enter and leave burrows, especially if vegetation is dense (Harris & Wanless, 2011).
  2. A specialist pair of Great Black-backed Gulls would take in excess of 30 Puffin adults over the course of the breeding period. However, this figure is based on corpse searches carried out at the end of the breeding season on Craigleith and Isle of May[36] and will be an underestimate, as a proportion of birds will have already been consumed. If 3 Great Black-backed Gull pairs were fed (as was the case in the Red Kite and Kestrel studies), it could save a minimum of 90 adult Puffins, as well their dependent chicks (assuming that Puffins present will be part of a breeding pair). Specialist Great Black-backed Gull pairs also feed their chicks on pufflings (and rabbit), so assuming a predation rate of 3 Pufflings per Great Black-backed Gull nest per day and a 30 day chick period then 90 pufflings would be predated by a specialist pair over the course of a breeding season. On this basis feeding 3 specialist nests could (if successful) result in a saving of around 270 pufflings.
  3. Great Black-backed gulls also take eggs as well as adults and chicks. A study of Great Black-backed Gulls from Newfoundland showed that they exhibited a preference for Guillemot eggs, selecting them disproportionately to their abundance, and consuming 40% of Guillemot eggs laid at one site, Gull Island (Veitch et al. 2016). Work would be required to confirm whether this preference is exhibited locally, although it seems reasonable on the basis that Guillemots do not make nests but lay eggs directly onto ledges on cliffs, meaning that the eggs are more visible than those of the other species.
  4. Students from Aberdeen University have been investigating the impacts of Great Black-backed Gull predation of Puffins on Craigleith, following increases in Great Black-backed Gulls and declines in Puffins. In 2017, a corpse search at the end of the breeding season revealed over 130 dead Puffins[37]. In 2018, a repeat corpse search revealed 130 dead Puffins. Although most took small numbers only, one specialist pair had stockpiled 30 Puffin carcasses in a ‘midden’ (Figure 16, Forth Seabird Group 2019).
  5. There is currently a PhD student on the Isle of May researching the foraging ecology of Great Black-backed Gulls and their potential effects on Puffin populations. Results from tagging Great Black-backed Gulls showed that 3 out of 10 birds did not leave the island to forage offshore at all, instead relying entirely on auks (mostly Puffin) and rabbits. This study also showed that these specialist Great Black-backed Gulls nested on their own outside the main colonies (S. Lopez, pers. comm).
  6. Corpse searches carried out on the Isle of May in 2017 and 2021 revealed that 570 and 500 adult Puffins were taken by Great Black-backed Gulls during these years respectively[38]. Around 10% of the 79 pairs currently breeding on the Isle of May are believed to be Puffin specialists, although almost all Great Black-backed Gulls will take some Puffins and pufflings during the course of a breeding season. An earlier study when there were only 27 pairs of Great Black-backed Gulls on the Isle of May, showed that 3 specialist pairs were responsible for the death of 96 Puffins, half of the total number found during corpse searches (Finney 2002).

Figure 7.1:
A ‘midden’ of more than 30 dead Puffins found in the territory of one pair of Great Black-backed Gulls on Craigleith, August 2018. (Taken from Forth Seabird Group 2019).

Figure 7.1: A ‘midden’ of more than 30 dead Puffins found in the territory of one pair of Great Black-backed Gulls on Craigleith, August 2018. (Taken from Forth Seabird Group 2019).

 

  1. Stable isotope analysis is currently being carried out on feather samples taken from Great Black-backed Gulls that have been ringed on the Isle of May, and it is hoped that there will be differences in signature between specialists and non-specialists. If so, it is possible that this technique can be used to confirm the prevalence of specialists within the colony. Current knowledge is based on pellets, which give an incomplete picture of colony behaviour (as some birds pellet in inaccessible areas). Stable isotope analyses of feathers would also help answer other questions about specialists, for example whether specialists are mostly male, and whether both members of a pair specialise. If the technique is successful, it could be employed at other colonies and for other species (e.g. Herring Gulls).
  2. Other unanswered questions include understanding why Great Black-backed Gulls choose to specialise, and whether feeding at a higher trophic level is more desirable than taking marine prey[39]. At present there does not seem to be any differences in productivity between specialists and non-specialists, although further years data are required to confirm this. It is also unclear whether another specialist will colonise if a specialist pair is removed, and whether the chicks of specialists become specialists themselves when they return to breed 5 years later.
  3. However, it is known that the proportion of Great Black-backed Gulls that hunt Puffins varies markedly between colonies, and therefore what is observed on the Isle of May might not be representative of the situation at other local SPAs. For example, on North Rona in the early 1970s there were ~2000 pairs of gulls and 6,000 pairs of Puffins and only 93 dead Puffins were found during corpse searches (Evans 1978). By contrast on Dun (St Kilda) the 30-40 pairs of Great Black-backed Gulls were all Puffin specialists and over a period of 4 years, these gulls killed at least 5,500 Puffins. It is of note that more Puffins were taken from an area where burrow density was low (5% compared to 1% of main colony), with the gulls selectively targeting immature birds (Harris 1980).
  4. A recent study analysing 1,035 pellets from Great Black-backed Gulls on Skokholm showed that overall Great Black-backed Gulls fed on seabirds with 48% taking mostly Manx Shearwater, 38% taking mostly Rabbits and 7% taking anthropogenic waste and 7% taking marine prey. Generalist pairs comprised 73% of the population with the remaining 27% being specialists. Of these specialist pairs, 5 were seabird specialists and 2 were mammal specialists. There were no links between diet and breeding success (Westerberg et al. 2019).
  5. Although specialist Great Black-backed Gulls have been identified on both on the Isle of May and Craigleith, it is possible that there may be specialists at other locations where Puffins and Great Black-backed Gulls nest in proximity such as Fidra, Inchkeith, Inchcolm Fowlsheugh, Longhaven and the Farne Islands. Although research has focussed on Puffins, the chicks of Kittiwakes, Guillemots and Razorbills will also be routinely taken by Great Black-backed Gull. 

7.2.3.    Herring Gull

  1. Herring Gulls predate the chicks and eggs of Puffins, Guillemots, Razorbills and Kittiwakes. They also impact on the auk species through kleptoparasitism[40]. Kleptoparasitism can be damaging because the chick may remain unfed for a significant amount of time (due to the long duration of many foraging bouts) at what is a critical growth period. In one part of the Isle of May on average 37% of Puffins bringing in fish were attacked and there was a negative relationship between Puffin recruitment and gull density (Harris 2011). However, looking at the Isle of May as a whole, only 7% of loads were lost, and there was no evidence that kleptoparasitism resulted in any detectable impact on reproductive output. At another site (Great Island), Puffins chose to nest in areas with high densities of Herring Gulls, perhaps because they gained some protection from Great Black-backed Gulls and Ravens by doing so (Pierotti 1983).
  2. It is known from various studies that Herring Gulls can specialise on other seabird species. For example, a study of Herring Gull predation of Lesser Black-backed Gull chicks carried out in the Gulf of Finland showed that two pairs of Herring Gulls were responsible for 17% of chick deaths. Once these predators were culled, predation rate reduced to 2% and fledging success improved significantly. However, ‘long-distance’ predation of chicks by Herring Gulls nesting elsewhere continued as these birds were hard to track and remove. This resulted in a decision to cull Herring Gulls by removing eggs from the entire Söderskär archipelago. During 4 years Herring Gull numbers were reduced by 40%, but this still did not stop the ‘long-distance’ predation. Although this study was carried out some years ago, it demonstrates the influence that specialist predators can exert (Hario et al. 1994).
  3. Another study of Herring Gulls in Newfoundland showed that 75–80% of Herring Gulls specialized on either intertidal organisms, human refuse, or other seabirds, while only 20–25% had generalized diets. Specific types of specialists tended to nest in particular habitats, and the study concluded that choice of nesting habitat may actually constrain diet choice. Whilst the intertidal specialists laid larger and heavier clutches, there were no significant differences in fledging rates, indicating the importance of other factors in fledging success as well as energy from prey (Pierotti & Annett 1991).
  4. A contrasting study of Herring Gull predation on Ring-billed Gulls Larus delawarensis nesting at Lake Ontario showed that predation was opportunistic, occurring primarily when Ring-billed Gulls entered the territory of Herring Gulls. Dietary studies revealed that nearly all Herring Gulls ate birds, but otherwise had a broadly similar diet, with birds accounting for a third of prey at most. These Herring Gulls could not be classified as bird specialists; predation of birds was generally infrequent, predation attempts were also often unsuccessful, and overall bird prey was considered insufficient to meet energetic requirements (Ingraham et al. 2020).
  5. Anecdotal evidence suggests that there may be Herring Gulls on the Isle of May that specialise on Kittiwake chicks: some individuals have been observed on multiple occasions watching Kittiwake nests, waiting for the moment that the adults swap over to then make their attack on the chick (F. Daunt, CEH, pers. comm.). A few Herring Gulls are also known to specialise in catching young Puffins while they are exercising their wings or when they are fledging (Harris 2011).
  6. There are a large number of Herring Gulls nesting alongside or in relatively close proximity to Kittiwakes and auks at a number of sites locally, including St Abbs to Fast Castle SPA (172 AON) Fowlsheugh SPA (1055 AON), and the Forth Islands SPA (5,964 AON) (JNCC 2021[41]). Within the Forth Islands SPA the Isle of May, Craigleith and Fidra support the largest Herring Gull colonies with 3061 AON, 1092 AON and 1059 AON respectively (Forth Seabird Group 2018 & 2019), with smaller numbers present on Fidra, Bass Rock, Inchcolm, Inchgarvie, Inchmickery, Inchkeith, Carr Craig, Haystack and Lamb. Small numbers are known to nest on Dunbar Castle, and also in Eyemouth town. There are likely to be other urban nesting locations in addition to these. Further investigation of the impacts of Herring Gulls on the key species at local colonies could clarify the likely scale of predation.

7.2.4.    Other Predators

  1. Several corvid species may steal seabird eggs, such as Crows, Magpies, Jackdaws and Ravens. Some may also take chicks, as a camera trap study on North Ronaldsay reveals (Figure 7.2, taken from Johnston et al. 2019).
  2. A review of studies looking at predation as a limiting factor for bird populations concluded both that generalist predators such Crows (and Foxes) occur at high densities in the UK compared with other European countries, and that ground-nesting seabirds, waders and gamebirds can be limited by predation (Roos et al. 2018). In this study shearwaters, storm petrels, gulls, skuas, terns and auks were classified together as ‘seabirds’. After an experimental removal of predators, the majority of cases involving seabirds (80%) and gamebirds (81%) found an increase in the population size of the prey species, whereas this effect was smaller for other groups such as waders (45%), Passerines (40%) and Raptors and owls (33%). The paper concludes that in the long-term further investigation of land-use practices and landscape configurations should be undertaken to reduce predator numbers (Roos et al. 2018). Although these results are based on a review of multiple studies across a number of species groups, the results indicate that the impacts of corvid predation on seabirds is an area worthy of further study.

Figure 7.2:
Camera trap photograph of Hooded Crow predating a Black Guillemot chick, 6 July 2017 on North Ronaldsay. Taken from Johnston et al. 2019

Figure 7.2: Camera trap photograph of Hooded Crow predating a Black Guillemot chick, 6 July 2017 on North Ronaldsay. Taken from Johnston et al. 2019

 

  1. Lesser Black-backed Gulls are generalist and opportunist feeders, known to take a range of marine prey, fisheries discards and human refuse (Mitchell et al. 2004). Even though they are classified as ‘generalist’ feeders, some individuals choose to specialise (Juvaste et al. 2017). Documented examples include specialisation on fisheries discards (Tyson et al. 2015), worms (Coulson & Coulson 2010) and human refuse (Juvaste et al. 2017). Although Lesser Black-backed gulls can and do take the chicks of other species, there is less evidence that individuals become seabird chick specialists.
  2. Great Skua it is a significant predator of Kittiwakes and auks. For example, on Foula (Shetland) Great Skua predation reduced the Kittiwake population by 54–85% between 1981-1995 (Heubeck et al 1999). It has been calculated that a 5% increase in seabirds in Great Skua diet at Foula is equivalent to consumption of an extra 1,000 Fulmars or 2,000 Kittiwakes (Votier et al. 2004a). A different study of Great Skua diet carried out on Hermaness (Shetland) showed that Great Skuas predated 12,500 and 13,000 seabirds in 1999 and 2001 respectively. In both years their prey was predominantly auks, with 7,837 taken in 1999 and 7,125 in 2001. Kittiwakes were also a significant prey item with 417 taken in 1999 and 285 in 2001 (Votier et al. 2004b). There are indications that rate of Great Skua predation on seabirds in some locations is unsustainable (Heubeck et al 1999, Regehr et al 1996), a situation that will have worsened following changes in fisheries policy and discard bans. Since there are no Great Skuas breeding within the Firth of Forth, Great Skua is not a problem locally. However, further investigation of Great Skua predation on auks and Kittiwakes elsewhere could be considered if further compensation is needed.
  3. Although this review has focussed on the species thought most likely to operate in this locality, sometimes unexpected specialist predators can occur. For example, in 2010 a Montagu’s Harrier Circus pygargus appeared at RSPB Minsmere (Suffolk) and stayed for two weeks during which period it took a large number of duck, wader and gull chicks.[42]

7.2.5.    Summary

  1. There is reasonable evidence to suggest further investigation and in some instances trials of DF of other specialist avian predators could lead to success in reducing predation pressure on SPA populations of Kittiwake and auks. However, due to lack of support this work is not being taken forward.
  2. Although recent studies suggest that in many cases specialist Great Black-backed Gulls nest well away from the main colony, occupying their own territory in which they forage primarily on Puffins and rabbits (S. Lopez pers. comm.) and there is clear evidence to suggest that a small number of specialist Great Black-backed Gulls exert significant predation pressure on both adult Puffins and pufflings (as well as Razorbill, Guillemot and Kittiwake chicks), it was felt that DF of Great Black-backed Gull was not feasible on the basis that many birds nest colonially. Further investigation into the impacts of specialist Herring Gulls Larus fuscus on Kittiwake on the Isle of May (where the Herring Gull colony numbers 3,398 AON – The Forth Seabird Group 2019) was also rejected for the same reasons. There was a general reluctance to engage with measures to reduce predation pressure as a means of compensating for the potential impacts of the wind farm due to concerns regarding any undesirable or unforeseen impacts on predator populations. These concerns were not alleviated by suggestions that further study into the potential use of DF could be conducted as a research trial through a reputable academic institution.

7.3. Supplementary feeding of Puffin & Kittiwake

7.3.1.    Background

  1. The principle of supplementary feeding is to provide additional prey to chicks to support growth and development and ultimately colony productivity (if feeding is undertaken at sufficient scale). For this to work there must be a close link between prey supply and breeding success as is thought to be the case for Kittiwake (Carroll et al. 2017).
  2. Accordingly, the technique seems most likely to be successful when prey supply would otherwise become limiting and is perhaps of particular benefit to those species that lay several eggs and typically hatch more than one chick. In this situation the disadvantages experienced by the later hatching chick or chicks may theoretically be overcome with additional food provided that the prospects for survival are linked to prey supply and not driven by obligate siblicide for example.
  3. As a general principle, supplementary feeding is, of course, less desirable than measures directed towards improving the natural prey supply by a variety of means, or in the case of competing commercial fisheries, to leave ‘enough for the birds’ in the first place (Cury et al. 2011).
  4. Species that have a more restricted diet as specialists for one reason or another, may conceivably be more likely to benefit from than generalists, that may be able to switch to alternative prey relatively effectively should the supply of preferred prey become limiting. At least on the Isle of May and perhaps at other locations in and around the Firth of Forth, Puffin and Kittiwake are seen to be sandeel specialists (see Wanless et al. 2018) and it is envisaged that these species would benefit most from supplementary feeding. This is exacerbated by the fact that sandeels are prone to considerable fluctuation in abundance with an increasing prospect of poor recruitment as the climate warms promoting the prospect of mismatch between the timing of hatching of 0-group sandeels relative to their copepod prey.
  5. In fact, studies trialling supplementary feeding of both Puffin (Harris 1978) and Kittiwake (Gill et al. 2002) have been undertaken that show it can be an effective means of improving productivity especially if prey availability is limited and the adults are struggling to provision effectively. However, where prey supply is already adequate, supplementary provisions to a single chick in particular may have the effect of reducing the demands upon the parents, which in turn provision the chick less. In effect, there is no net gain in provisions for the chick and this may then become dependent on those provisions.
  6. Supplementary feeding of Kittiwake and Puffin during years of poor prey supply in particular has clear potential to be worthwhile. Whilst it is not desirable to feed birds regularly and certainly effort is better directed towards protecting prey offshore, it is considered that the decline of Kittiwake in particular is serious enough to warrant consideration of alternative techniques such as supplementary feeding that have not been trialled before in the UK.
  7. Although the concept has merit, and there is some scientific evidence to suggest it could be successful, a proof of concept trial would be required for Kittiwake to ensure that food could be delivered to nests without causing disturbance. However, ultimately the possibility of carrying out supplementary feeding was dismissed due to lack of stakeholder support. Nonetheless a description of how the work could be approached is included below.

7.3.2.    REVIEW of MEASURE

  1. Supplementary feeding of Puffin chicks is technically straightforward as fish can be deposited directly into the burrow mimicking prey delivery by provisioning adults (Harris 1978). As a result, relatively large numbers of birds could conceivably be efficiently treated in a high-density locality such as the Isle of May once the logistics of a sufficient prey supply, such as frozen Sprat as used by Harris (1978) has been overcome.
  2. Supplementary feeding Kittiwake chicks is more complex as a result of their use of open nests sites, where neighbouring adults or other species (e.g. larger gulls or even corvids) may scavenge prey from them. In addition, chicks beg the returning adults for food, and it is this begging action that prompts the adult to regurgitate prey directly into the chicks gullet These complexities were overcome in an Alaskan study (Gill et al. 2002), although the study site is somewhat unique (discussed further below). For supplementary feeding to work well in the UK, the site would need to be selected carefully.
  3. Given the key differences between Puffin and Kittiwake, a burrow nesting species with a single chick and an open-nesting species with multiple chicks respectively, the two species are discussed separately below.

Supplementary feeding Puffin chicks

  1. Three studies involving supplementary feeding of Puffin chicks in Scotland were carried out some decades ago: one on St Kilda (Harris 1978) and two on the Isle of May (Harris 1978, Cook & Hamer 1997). Supplementary feeding has more recently been carried out in Norway on the Røst archipelago (Dahl 2005), where poor prey availability has led to a decrease in Puffin numbers of 81% between 1979–2019 (Fayet et al. 2021), including total breeding failure between 2007 and 2015.
  2. The study by Harris (1978), which trialled supplementary feeding on St Kilda and the Isle of May found that Puffin chicks at St Kilda fledged at significantly higher weights if they were provided daily with 50 g of sprats compared to control chicks (average weight of 316 g for 11 fed chicks vs. 301 g for 37 control chicks). Five chicks were removed from burrows and fed sprats ad libitum, and these chicks were even heavier (365 g), while three unfed chicks with a single parent were lighter (240 g). All removed chicks and fed chicks fledged, 37 of 39 controls fledged and three of six single-parent chicks fledged. There was no difference in fledging age between fed and control chicks (40 days), but single-parent chicks took longer to fledge (45 days). By contrast, Puffin chicks on the Isle of May exhibited smaller differences between treatments. Six chicks were removed and fed ad libitum, and these weighed on average 367 g. Ten chicks were fed with 50 g of sprats per day, and weighed 344 g. Control chicks weighed 331 g, whilst chicks of single parents weighed 303 g. Comparison of the data from St Kilda and the Isle of May suggests that the St. Kilda puffins were to some degree food limited, whereas those on the Isle of May were not at that time.
  3. A further supplementary feeding study on the Isle of May (Cook & Hamer 1997) was carried out to investigate whether there was a causal relationship between the nutritional status of pufflings and the subsequent rates of food provisioning by their parents. This study showed that chicks given supplementary food received less frequent meals from parents than control chicks, indicating that parents adjusted their foraging effort based on the nutritional status of the chick. If the growth rates of chicks were limited by poor food supply and adults delivered food as rapidly as they could, then regulation of food delivery would not be expected.
  4. Supplementary feeding of Puffin chicks on the Røst archipelago in Norway confirms that when chicks are fed parents reduce their foraging effort and the chicks do not receive any extra nutrition (Dahl et al. 2005). Whilst the study concluded that feeding conditions were adequate for normal breeding, further failures on the Røst archipelago indicate that prey is limiting and recent work at this site links large foraging ranges to lower chick provisioning rates (Fayet et al. 2021).
  5. Both of the studies carried out on the Isle of May discussed above were undertaken during a period when the Puffin colony was experiencing a period of rapid growth; conditions were considered to be favourable and chicks were rarely observed begging for food (Harris 1978). Figure 8.3 shows that since the latter Cook & Hamer (1997) study Puffin numbers have significantly declined, and it is anticipated that a further trial of supplementary feeding on the Isle of May will yield a different set of results.

Figure 7.3:
Numbers of breeding Atlantic Puffin expressed as Apparently Occupied Burrows (AOB) from the mid 1980s up to 2019, both in the UK according to the two most recent censuses and at selected SPAs or reserves on the east coasts of Scotland and England.

Figure 7.3: Numbers of breeding Atlantic Puffin expressed as Apparently Occupied Burrows (AOB) from the mid 1980s up to 2019, both in the UK according to the two most recent censuses and at selected SPAs or reserves on the east coasts of Scotland and England. 

 

Supplementary feeding Kittiwake chicks

  1. The supplementary feeding study at Middleton Island, Alaska (Gill et al. 2002) represents the only one yet conducted on Kittiwakes. In this study, both Kittiwake adults and chicks were fed on Herring ad libitum over two breeding seasons, and a range of parameters considered likely indicators of nutritional status were studied and ranked. Comparison of breeding performance were made between fed and unfed nests. Parameters considered included egg size, phenology, adult and chick behaviour, parental attendance, chick growth and survival and breeding success (Gill et al. 2002).
  2. Breeding success (specifically fledging success, hatching success and overall productivity), adult incubation and attendance during chick rearing and chick growth parameters (especially for the ß-chick[43]) were key variables that were positively influenced by supplemental feeding. Supplemental feeding improved fledging success of fed pairs by 6–8 standard deviations over unfed pairs, and hatching success was enhanced by 2.5–6 standard deviations (Gill et al. 2002).
  3. Kittiwakes typically lay either 1 or 2 eggs, although 3 is also possible. However, the latter is rarely recorded at colonies in the Firth of Forth for example. In clutches of more than 1 egg, laying occurs at about 2 day intervals, but sometimes there may be a delay to a third day. Hatching of eggs is asynchronous by about a day and occasionally longer. Single-egg clutches and the last egg in a 3-egg clutch have the lowest chance of producing a fledged chick. In 2-egg clutches, the first-laid egg is more successful than the second egg (Coulson 2011).
  4. There are reasons why the second chick (or ß-chick) is less successful: the first or α-chick learns to beg for food from the adult before the ß-chick hatches. To be successful the ß-chick has to be able to beg effectively enough to persuade the parents to feed it instead of its older sibling. As the second chick usually hatches a day or so after the first, this delay in feeding sometimes results in a greater difference in size than would be expected based on hatching date alone. If there is a third chick, it often dies, as the third egg is smaller and has a smaller yolk reserve, and it must also overcome the same challenges to get fed. However, the death should not be attributed to food shortage, but rather to the difficulty in being able to beg effectively enough to persuade the parents to feed it despite competition from the vigorous begging of its larger siblings (Coulson 2011).
  5. Supplemental feeding has been shown to improve productivity by improving the growth rate of the ß-chick. Growth rate has an important effect on subsequent post-fledging survival during the following two years. Productivity of single clutches is actually lower than that of larger clutches: of single-egg clutches 67% of the eggs failed to produce a fledged chick. (The rationale behind this is that higher quality females lay more eggs). Even when first time breeders are accounted for this is still poor. However, Coulson (2011) suggests that the problem lies with incubation, which in most cases finishes before hatching could occur. If the egg hatches, fledging success is the same as other clutches.
  6. Therefore, it seems reasonable to suggest that supplementary feeding not only improves productivity in conditions where prey is short, but even when prey is available it could also increase productivity by improving the growth rate (and therefore survival prospects) of the ß-chick. In the Alaskan study supplementary feeding also improved hatching success, meaning that more ß-chicks hatched, which in turn then benefitted from the supplementary feeding, resulting in an overall improvement in fledging success. (It is not known whether supplementary feeding would help the third or γ-chick, as none of the nests in the Alaskan study had 3 chicks. The egg of the γ-chick is smaller, so it may be that the γ-chick still dies even with supplementary food; a situation that requires further study. However given that the Kittiwakes rarely lay three eggs in the Firth of Forth then this is not considered a priority).
  7. A second supplementary feeding study of Kittiwakes from Middleton Island also demonstrates the indirect benefits of supplementary feeding (White et al. 2010). Siblicide may be observed in Kittiwake chicks, where the α-chick harasses one of the other chicks causing it to fall out of the nest as a consequence (Dickens 1987, 2021). The α-chick may also administer brief ‘punishing pecks’ to the b-chick to stop the latter from begging for food from a parent (Dickens 2021). White et al. (2010) provided supplemental food to Kittiwakes over a whole breeding season and compared the aggressive behaviour of fed chicks and control chicks. Control α-chicks showed more frequent and intense aggression than the fed α-chicks. The consequences of increased aggression for ß-chicks were lower begging rate, lower growth rate and lower survival rate. Thus, a sustained increase in food availability reduces broodmate aggression and improves ß-chick survival rates.
  8. It is also conceivable that supplementary feeding may encourage other birds to nest at the site resulting in a larger colony. This may have benefits, for example, in colony defence from potential predators.  
  9. Although it seems likely that supplementary feeding would result in improved fledging success, there are some logistical issues. The Alaskan studies were carried out on Middleton Island where Kittiwakes nest on an abandoned radar tower that has been purposely adapted to carry out seabird research. The Kittiwakes nest behind removable panels, so that they can be fed, captured and weighed regularly (Figure 8.4).

Figure 7.4:
Kittiwake colony on Middleton Island, Alaska. A converted radar tower fitted with removable panels enables easy access to nest sites for supplemental feeding and monitoring. (Photos by Jon Green).

Figure 7.4: Kittiwake colony on Middleton Island, Alaska. A converted radar tower fitted with removable panels enables easy access to nest sites for supplemental feeding and monitoring. (Photos by Jon Green).

 

  1. The trial site would need to be selected carefully as it would be difficult to carry out supplementary feeding at an open nest site where Herring Gulls and other scavengers would compete for the food. The site would need to be easily accessible and some means of depositing fish directly into the nest is required. Preliminary discussion with researchers suggested some form of tube system could be successful, with this retaining having a lid and with sufficient lubrication and/or some form of propulsion mechanism to ensure fish is delivered successfully. However, a portable rather than a fixed system is much preferred and at this stage, a very lengthy but still portable blow-pipe, may be the answer. Considering that technique development is required, a proof-of-concept trial would be needed in the first instance. 
  2. The lack of stakeholder support and limited potential compensation benefits meant that this measure was not taken further.

7.4. Removal of plastic from the Firth of Forth

7.4.1.    Background

  1. Plastic pollution is now a universal issue for seabirds although the biological significance of ingestion is still unquantified at a population level. Even individual cases definitively attributing seabird mortality to plastic ingestion are rare (Pierce et al. 2004). This is because clinical data on the bird’s health is required when it is alive, followed by a necropsy. One documented example relates to an emaciated gannet brought into a wildlife rehabilitation centre, unable to stand or feed. It died shortly afterwards with necropsy confirming the cause of death was due to a blockage to the oesophagus caused by a bottle top. Patterns of ulceration in the gizzard show that the bottle top had also previously been lodged there too (Pierce et al. 2004). Ingestion of plastics in general is likely to be exacerbated by poor prey availability as hunger reduces prey discrimination.
  2. Plastic may impact on seabirds in various ways: it may be ingested resulting in a range of lethal and sub-lethal effects or incorporated into nests where it may cause entanglement (Votier et al. 2011, Roman et al. 2020). Physical impacts of plastic ingestion include suppression of appetite and lack of energy, which may impact on ability to forage and reproduce. In severe cases ingestion may causes blockages and death (Pierce et al. 2004, Roman et al. 2020). Plastic ingestion also has chemical effects, concerning the transfer of plastic-additive and plastic- adsorbed chemicals (Roman et al. 2020).
  3. CEH regularly collect dead Puffins found on the Isle of May to monitor them, and a routine dissection showed that many contain nurdles (small industrial pellets used to make plastic). It is considered highly likely that Guillemot, Razorbill and Kittiwake will also contain high levels of nurdles, especially Kittiwake as they pick small items off the surface (F. Daunt CEH, pers. comm). Nurdles resemble fish eggs, making them attractive to many marine species. Persistent organic pollutants from the surrounding seawater adsorb onto the surface of nurdles, concentrating toxins to levels millions of times higher than the surrounding water (Mato et al. 2001). Beaches around the Firth of Forth, in particular Queensferry, are known to have high numbers of nurdles[44].
  4. Understanding that prey abundance is low and that plastic pollution is a problem within the Firth of Forth, then reducing marine plastics is intuitively beneficial both for seabirds and other marine life, although quantifying the benefits is unfortunately not possible. Whilst nurdles cannot yet be removed from the marine environment, user plastic certainly can be, and relatively straightforward solutions are available. Beach cleans and regulation of rubbish entering watercourses are effective. Marine litter can also be removed by other methods such as clean-up vessels (purpose designed vessels to clean-up harbours) and through novel technologies currently under development by companies such as Icthion, including filters that can be retrofitted to shipping vessels to collect plastic without impacting on marine life. Although fitting filters to vessels could not be viewed as compensation per se, it is possible that these kinds of initiatives could be incorporated into elements of the project further down the line.
  5. The possibility of initiating further work on nurdles and seabirds within the Firth of Forth was discussed with Fidra, an East Lothian based charity that has pioneered work on nurdles and which runs The Great Nurdle Hunt, an initiative that encourages the public to look for nurdles and submit data in order to improve awareness and target potentially polluting industries. However, Fidra do not work directly on seabirds, and on this basis the possibility was discounted.
  6. Beach cleans and regulation of rubbish entering water courses was pursued instead. One possibility identified was re-invigoration of the Forth Estuary Forum’s Coastal Litter Campaign (Storrier et al. 2004), which ran for three years between 2001 and 2004, and made substantial progress towards a ‘litter-free Forth’. The project used a team of volunteers, who used a scientifically standardised technique to assess trends in the deposition of fresh marine litter each month. The campaign found that the majority of the litter came from land-based sources, which became the focus of their campaigns. However, The Forth Estuary Forum did not respond to our invitation to discuss this further in time for the compensation scoping process, although a reply was received some months later indicating that a collaboration to tackle plastic pollution in The Forth Estuary would be of interest.
  7. Stakeholder consultation relating to potential rodent eradication from Inchcolm revealed minor issues with plastic pollution, and as a result removal of plastic litter from beaches was incorporated into work proposed at this site (see Section 2.3).
  8. Ingestion of plastics in general is likely to be exacerbated by poor prey availability as hunger reduces prey discrimination. Understanding that prey abundance is low and plastic pollution is a problem within the Firth of Forth, then reducing marine plastics is intuitively beneficial both for seabirds, seals and other marine life, although quantifying the benefits is unfortunately not possible.
  9. Feedback from NatureScot indicated that whilst they agreed that removing plastics would have positive effects, they did not consider that it could be classified as a compensatory measure because the benefit is impossible to quantify[45]. On this ground further work on reducing the impacts of plastic pollution on seabirds has not been pursued.