Re-introduction of pine marten in England

Contents

• GWCT position
• Background
• Key considerations for pine marten re-introductions
• Implications of the protected status of pine marten
• Grey squirrel control
• Predation impacts
• Socio-economic and human considerations
• Release vs natural expansion and genetic integrity

GWCT position

The Game & Wildlife Conservation Trust (GWCT) supports re-introductions of native species provided International Union for Conservation of Nature (IUCN) and Department of Environment, Food & Rural Affairs (Defra) guidelines are followed. Monitoring the success and impacts of re-introductions and the development of mitigation and exit strategies are key elements that need to be effective. We are concerned that these have not been adequately demonstrated in pine marten projects to date and that mitigation strategies are limited by their status as a Schedule 5 species. Appropriate levels of intervention in relation to managing the impacts on other species (especially those at-risk), human property, business and game interests, and livelihoods must be a primary consideration in the sanctioning of further re-introductions.

Photo credit: Laurie Campbell

Given paucity of data on population dynamics post release, it is unclear whether there is a net benefit to ecosystem recovery. Whilst pine martens are seen as a possible ‘natural’ means of controlling grey squirrel numbers, there is a real risk that the direct and cumulative effects on vulnerable species will never be quantified due to a lack of baseline data and the difficulty and expense of monitoring at scale.

Consequently, the GWCT believes that, until more data are available, there is a profound policy contradiction in wishing on the one hand to secure recovery of at-risk species and, on the other hand, undertaking planned reintroductions of more predators of that species. Future pine marten re-introduction should be undertaken with considerable caution given the lack of evidence and consequent inability to quantify risks.

Given anecdotal and other evidence (see section 8), natural expansion, whilst taking longer, could achieve policy ambitions. More research is needed and where the aim of re-introduction projects is to encourage dispersal and recolonisation of their former range, proposals for re-introduction in adjacent regions should be assessed in this context.

Where re-introduction is considered feasible:  

• We believe that more comprehensive monitoring is required. Consideration should be given to monitoring for a period of 15-20 years post-release with a five-yearly assessment and review.
• A mitigation strategy must be put in place with a satisfactory process for obtaining the necessary licences for control if required. This could take the form of a wildlife management licence based on approved methods of lethal control. However, the legal status of pine marten would need to be reviewed in order to make this possible.
• More extensive long-term monitoring is needed to properly understand dispersal dynamics (including habitat usage in lowland open landscapes) and impacts of existing projects.
• People and businesses in and around the release area are consulted and any impacts recorded.

Background

The GWCT has extensive experience of pest and predation management through research into methods of control and animal behaviour and practical experience in working with gamekeepers and pest controllers in the wider countryside. Our involvement with pine marten is related to their co-existence with capercaillie and conflicts with capercaillie conservation.

Key considerations for pine marten re-introductions

1. The IUCN guidelines on re-introductions require the formulation of an exit strategy and an ongoing monitoring programme. Existing pine marten re-introductions have not addressed these elements sufficiently. Consequently, no strategies have yet been tested and the resource needed for effective mitigation may not be available.  
2. Experience with other protected species suggests that there is likely to be a reluctance to grant control licences. For example, the National Gamekeepers Organisation had to take Natural England (NE) to judicial review over buzzard control and practitioners have failed to secure licences from NE to control rooks and jackdaws to conserve grey partridges, even though their control is permitted to “prevent serious damage” to crops and livestock.  
3. The Schedule 5 (Wildlife & Countryside Act 1981) status of pine marten limits the options for developing a robust and effective exit or mitigation strategy where impacts are excessive or unacceptable. Further, they can only be caught in a live capture trap that meets the Agreement on International Humane Trapping Standards (AIHTS), of which there are currently only two approved for pine marten. Other live-trap designs may be used under special licence, but captives must be inspected by persons qualified to undertake a full welfare assessment against AIHTS criteria, which may be impracticable. IUCN re-introduction guidelines can only be achieved if the legal status of the pine marten is changed. 
4. Monitoring within current re-introduction projects is limited to the first year of release, with no monitoring of offspring. IUCN guidelines require monitoring to continue beyond the project so any additional intervention can be evaluated. We are not aware of any follow-up assessment of these projects other than the results of their post-release movements. Consequently, it is unclear whether there is a net benefit to ecosystem recovery from pine marten re-introduction. Equally neither is there sufficient evidence of negative impacts for the same reason. 
5. It is a real risk that the direct and cumulative effects of pine martens on vulnerable species will never be quantified due to the practical difficulty and expense of monitoring at scale, the fact that no local baselines will exist, and the scientific impossibility of quantifying the impact of individual predator species. Available evidence points to the need for trade-offs, given the likelihood of increased predation of at-risk species such as red squirrel, due to direct, cumulative and competition effects.

Implications of the protected status of pine marten

1. Pine martens are listed under Schedule 5 of the Wildlife & Countryside Act 1981; consequently, it is illegal to kill, injure and disturb a pine marten or to disturb or intentionally obstruct an occupied place of rest. This protected status requires the licensed use of AIHTS-approved traps for their control and creates consequences for other legal trapping practices undertaken for conservation and pest control purposes.   
2. The control of rats, grey squirrels and other mustelids in spring traps set in tunnels is important for disease control, protecting trees planted to meet net zero targets, wild game management, and the conservation of red-listed birds (in particular curlew, lapwing and spotted flycatcher). The tunnels in which traps are typically set include external excluders and internal baffles with excluder apertures recommended to be 50mm square or core-drilled, to minimise risk of non-target captures. However, adult pine martens are known to be able to squeeze through a 45mm gap, and juveniles will pass through smaller gaps still, so in areas where release is targeted, tunnel trap users would need to be informed and excluder configurations altered accordingly. Research by the GWCT has shown that physical excluders on tunnel traps, used to prevent access by adult pine martens and polecats, also reduces captures of grey squirrels and rats.
3. Risk of accidental capture of pine martens in these traps lawfully set for grey squirrels and other mammalian pest species is therefore a concern. Whilst the Wildlife & Countryside Act 1981 would seem to provide a defence, either due to “the act [being] the incidental result of a lawful operation and could not reasonably have been avoided” or the “action was necessary for the purpose of preventing serious damage to livestock, foodstuffs for livestock, crops, vegetables, fruit, growing timber or any other form of property or to fisheries” (although note not for conservation purposes), the legal ramifications of kill-trap use in areas where pine martens are at risk, is unsupported by case law, and so what constitutes a reckless act is not yet clear. Guidance from Defra is required so that best practice guidance can be formulated.
4. Pine martens will also be at risk of capture in live-capture traps that can lawfully be used to control common pest species but which are approved for particular species. There are only two AIHTS-approved live-catch traps for pine marten but these traps are not approved for stoat, another AIHTS-listed species, commonly targeted in wild game management, for which wildlife managers are legally obliged to use different traps again.
5. Uncertainty and lack of Defra-endorsed legal guidance on trap choice and what constitutes a reckless act could have consequences for the conservation of a wide range of at-risk species that benefit from the deployment of traps for game and wildlife management or woodland protection purposes by burdening wildlife managers with an added layer of risk management and legal uncertainty.

Grey squirrel control

1. We believe that agencies such as Forestry England and conservation charities promote pine marten re-introduction as a ‘natural’ solution to the control of grey squirrels given the increased focus on animal welfare. Forestry England is supportive of pine marten reintroductions given the dual benefits of a sighting likely to increase public footfall to their sites (and therefore, revenue), and the possibility of grey squirrel control, given the ‘no control’ policy across most of their sites, at least in the south.
2. However, the benefits of pine marten reintroduction to grey squirrel control should be tempered by the knowledge that their habitats do not necessarily overlap, that pine martens may avoid human-dominated landscapes where grey squirrels persist (creating urban refuges for the grey squirrel), the effects are likely to be localised and that there remains the possibility that grey squirrels will develop a genetic fear response to pine marten presence over time. Consequently, pine marten should not be seen as an excuse to reduce human intervention in controlling grey squirrels in support of red squirrel conservation or for pest control purposes in woodland.
3. The potential role of pine marten in protecting woodland from damage by suppressing grey squirrel populations has received much attention since its initial observation. Dietary analysis has shown that grey squirrel biomass occurs at a higher frequency than red squirrel in pine marten scats with a number of factors hypothesised as being responsible.  
4. Grey squirrels and pine martens do not necessarily have overlapping ranges given their habitat preferences but where this is the case grey squirrel is a relatively common food source in the spring and summer. As the grey squirrel is a non-native species, it is likely to be more naive to pine marten presence and therefore more vulnerable to predation.
5. Whilst these findings support the role of pine marten in grey squirrel control in localised areas of overlap, what is less known is the potential for the grey squirrel to develop anti-predator behaviour in a few generations.
6. In addition, in areas where pine marten and grey squirrel overlap and the need for grey squirrel control remains, there is the practical problem of risk of accidental capture in kill-traps as mentioned above. As pine marten are likely to investigate baits commonly used to attract grey squirrels to traps, there may need to be a complete switchover to AIHTS live-catch traps approved for use on pine marten only. These will require at least one daily trap inspection, with the attendant cost of new traps/extra labour requirements.

Predation impacts

1. Whilst predation is a natural process, the GWCT is concerned that the status of many predator-prey populations is no longer in balance. This is due to a number of pressures, not only habitat-related, but also high levels of predation by generalist predators, especially foxes and crows, which occur at high densities in the UK compared with other European countries (e.g. Roos et al. 2018) but also protected raptors and badgers.
2. It is vital that pine marten re-introductions provide for future control to support of conservation objectives.
3. In addition we reiterate our concern that pine marten re-introductions could have profound impacts on the legal trapping of predators and pests for conservation and game management purposes (see 4 above). 
4. Given the opportunistic foraging behaviour of pine marten, predation impacts will reflect the relative abundance, encounter rates and local habitat characteristics of the release sites and a ‘buffer zone’ around it as territorial expansion occurs in subsequent years. Potential impacts on frogs and toads, reptiles, birds and mammal species need to be considered. No studies have quantified the population-level impacts of pine marten on particular prey species.
5. The main conflict in Scotland relates to pine marten and capercaillie, a species not found in England. The UK capercaillie population has declined so rapidly that it is at very real risk of extinction (for the second time) and is a 'Red List' species. 
6. In England the area of greatest concern is the potential impact on breeding success, both of ground-nesting and tree-nesting species, through egg and nestling predation as these are currently unknown. However, in Sweden a wader recovery project in an agricultural landscape identified pine marten as one of the main predators. Therefore, although there are no recorded impacts in England, breeding waders of conservation concern, e.g. curlew, lapwing, redshank could be at risk where populations overlap with pine marten presence e.g. with curlew breeding in the New Forest.
7. Given the trends in bird populations identified above, adding further, cumulative predation pressure is a concern. Although the pine marten was native to England and so many of the potential prey species will have co-developed alongside it as a potential predator, the cumulative effect of pine marten predation over and above existing predators such as the fox, badger, corvid and raptor needs to be assessed at each proposed release site. The effects will not only be on the prey population but also potentially on the predator population if competing for a prey source. The most naturally abundant and easiest to catch prey is usually the field vole. But populations of field vole fluctuate and are the subject of predation from a wide range of predators resulting in pine marten competing for voles with species such as hen harriers and short-eared owls as well as reptiles.

Socio-economic and human considerations

1. There are a number of potential impacts of pine marten to rural businesses, communities and householders. 
2. Pine marten are not considered to be a threat to sheep, lambs or livestock due to their size and reluctance to venture into open ground away from cover. However, they are a threat to poultry keepers as, like foxes, they will kill at any time of the year, kill in excess of their immediate food needs, and so can devastate domestic flocks. They gain access to poultry pens as they are extremely agile and hen houses through gaps of about 50mm in diameter. Re-introduction projects point to simple husbandry that can minimise this risk such as shutting hens up before dark and ensuring houses are in sound condition. But in practice rats can create holes in sound houses, which are then used by the pine martens, and producers/farmers are tied to twice-daily attendance all year to open and close, unless investment is made in an expensive automated system. 
3. In addition, anecdotal evidence from Ireland suggests that pine marten may predate domestic and feral cats.
4. There are also potential impacts on game management. On lowland shoots that rely on reared game, pine martens are regarded as a potential threat to poults in release pens. This risk can be mitigated by using electric fencing around pens as for foxes and to avoiding low overhanging branches over release pens and within about 3 metres of the pen. On large shoots, these adaptations could be both costly and difficult, with the removal of cover opening up the canopy to further risk from aerial predation. However the GWCT’s main concern is predation once pheasant poults start leaving the release pen and spreading out into cover. Experience in Scotland is that pine martens had taken to hunting poults at roost, killing some, and disturbing many more resulting in them dispersing beyond shoot boundaries (and therefore ‘lost’ to the shoot). This could present a significant threat to lowland shoots, particularly in areas where lowland pheasant shoots are greatest in number and extent.
5. Where there is a scarcity of natural sites, pine martens may use both inhabited and uninhabited buildings. Where pine martens are in buildings they may create problems for the householders in terms of noise, smell and hygiene, and structural damage. The current approach is to encourage the householder to tolerate their presence until they naturally vacate in mid-summer. This is because excessive disturbance may cause the female to abandon her kits. Exclusion of breeding pine marten under licence is possible, although individual non-breeding pine marten may be humanely deterred or excluded from a dwelling without licence. Such mitigation approaches are necessary as the Schedule 5 protection means that in many cases householders are unable to protect their property from damage.

Release vs natural expansion and genetic integrity

1. Pine marten used to be a common species found across England wherever large tracts of woodland occurred, but by 1915 the species was confined to just a few of the more remote areas across Britain and Ireland.
2. Today, populations are expanding in number and range in Scotland (and Ireland). In England and Wales, the pine marten is the subject of re-introduction programmes in mid-Wales and the Forest of Dean led by the Vincent Wildlife Trust (VWT), Gloucestershire Wildlife Trust, Forest England and Wildlife Vets International.
3. Other free-living populations exist in England at very low densities with pine marten recorded in Shropshire, Northumberland and the New Forest, and occasional sightings in the Lake District and the North York Moors. Range expansion from populations in Southern Scotland is likely to be leading the re-colonisation of the border regions such as Kielder Forest in Northumberland.
4. Many free-living populations are known simply through wildlife camera ‘sightings’. For example in the New Forest, an ongoing camera trapping study by Wild New Forest (WNF) (contracted by Forestry England) is apparently achieving sightings widely over the Forest.
5. It is likely that in some of these free-living cases the genetic integrity of the population is questionable, with the possibility of populations building from zoo or wildlife park escapees. Official re-introductions will have used only native UK stock caught under licence from Scotland, whereas analysis of recovered carcases in the New Forest show that some originate from geographical separate areas.
6. As there is no functional residual population of pine marten in England, this would support re-introduction projects. However, the success of the southern Scotland and mid-Wales releases could provide a useful nucleus for expansion into northern and western England. Indeed, this is already being experienced in north Northumberland. In February 2021 the VWT reported that more than 50 records of pine martens had been collected across Northumberland. This reflects the natural tendency of all species to migrate to the most suitable habitat; a point noted by the VWT. Indeed, it is their hope that pine martens will naturally recolonise their former range outside of the initial release sites.
7. The IUCN guidelines require that the reasons for the decline/extinction should be addressed to allow ‘natural’ recolonisation before release. Given government policy emphasis on tree planting, the availability of suitable habitat and prey abundance are unlikely to be limiting factors.