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Title: The recovery of the polecat Mustela putorius in Great Britain
Author: Sainsbury, K.
ISNI:       0000 0004 8498 275X
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2019
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Many carnivore species are experiencing declines due to anthropogenic factors such as direct killing, habitat loss, secondary exposure to chemical control agents, and depletion of prey resources. Due to their top-down effects on the structure and function of ecosystems, carnivores are, however, increasingly the focus of efforts towards ecological restoration. To enable such restoration to take place, wildlife managers need to understand both the ecological processes and the social-ecological factors that may affect carnivore recovery and establishment. In this thesis, I use the European polecat Mustela putorius, which is currently recolonising Great Britain following near extirpation in the nineteenth century, as a case study through which to explore the processes of carnivore recovery. I investigate social and ecological risks to the polecat's continuing range and population expansion, which may also be pertinent to the wider challenges of carnivore conservation. In my introduction, I outline the importance of carnivores to ecosystem function and review the wide-ranging and cascading effects their reinstatement can have. I provide an overview of human-carnivore interactions and the anthropogenic processes that directly or indirectly lead to carnivore declines. I give a historical context to human-carnivore relations in Great Britain, introduce polecats, their biology and changing status and provide an overview of my research objectives and thesis structure. I then carry out a detailed literature review of the changing status of the eight terrestrial mammalian carnivores native to Great Britain. I summarise the anthropogenic processes that have influenced their status. I find that polecats have recolonised Great Britain less quickly than otters Lutra lutra but more quickly than pine martens Martes martes. Badgers Meles meles have increased in abundance. Foxes Vulpes vulpes are experiencing a decline and wildcat are imperilled by hybridisation with domestic cats. Stoats Mustela erminea and weasels Mustela nivalis are data deficient, but evidence suggests that stoats may be increasing in number relative to weasels. Next, I explore polecat resource use during a period of ecological change by analysing the stable isotopes of carbon and nitrogen from a museum collection of polecat whiskers. I find that variation in isotope ratios and isotopic niches indicate differences in resource use between polecats collected from the leading edge of the range compared to the established parts of the range and that this effect was greatest in the 1960s when rabbits Oryctolagus cuniculus-an important prey for polecats-were in low abundance. I also find that female polecats show greater variation in resource use than males, indicating that they may have different needs as part of conservation efforts. Next, I carry out a study of polecat diets to assess responses to fluctuating abundance of rabbits. I analyse the stomach contents from polecat carcasses collected between 2013 and 2016. I compare my results with those from earlier polecat dietary studies and find that the proportion of lagomorphs increased in polecat diet between the 1960s and 1990s. Although rabbit populations have been declining since the 1990s, I find no difference in the proportion of lagomorphs in polecat diet between the 1990s and 2010s. Secondary exposure to second generation anticoagulant rodenticides is a contemporary risk to polecat recovery that is also related to their diet, as polecats are likely exposed to rodenticides by eating contaminated rodents. In Chapter 5, I analyse the livers from polecat carcasses collected between 2013 and 2016 to measure current levels of secondary exposure and explore factors that may affect exposure. I find that the frequency of exposure to rodenticides was 79% in polecats and that this represents a 1.7 fold increase in exposure frequency over 25 years. I find that the probability of exposure increases with age and with increasing values of ẟ15N, suggesting that resource use influences polecat exposure to rodenticides. I then explore the principles underpinning modern gamekeeping practices, by carrying out interviews with gamekeepers to find out what they do and why. In this qualitative study, I analyse gamekeepers' conception of The Balance, which is an overarching narrative that they have adopted to explain their approach to wildlife management. Although The Balance includes echoes of the heuristic of the 'balance-of-nature', it is most often employed in the context of maximising shootable game surpluses while providing opportunities to other wildlife that do not conflict with this objective. I find that keeping The Balance requires a ritualised, highly interventionist approach to producing game that presents both risks and rewards to predators. The multiplicity of The Balance-in which gamekeepers are stewards of both game and the countryside-creates an ambiguity that, when associated with the regular culling of predators and negative perceptions of sport shooting, may cause misunderstandings between gamekeepers and other publics. In conclusion, I find that polecats have been able to recolonise most of southern Britain despite the risks of fluctuating rabbit populations, increasing exposure to rodenticides and predator controls. Polecat recovery has occurred with minimal direct conservation effort. It has also taken a long time: one hundred years after their population nadir, polecats are yet to fully recolonise their former range. More broadly, a low-intervention approach is unlikely to succeed, or be desirable, for all carnivores. In particular, those that are slower to mature, have lower reproductive rates, more specialised resource requirements and greater impact on anthropogenic practices, or where the potential ecological benefits that may be derived from a species' restoration necessitate an expedited recovery.
Supervisor: McDonald, R. A. ; Shore, R. F. ; Schofield, H. ; DeSilvey, C. Sponsor: People's Trust for Endangered Species ; Vincent Wildlife Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: carnivore ; environmental pollutant ; mustelid ; polecat ; wildlife conservation ; stable isotopes ; gut content analysis ; gamekeeping