Monitoring the return of the Polecat to the 'Far East'

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MAMMAL CONFERENCE

MONITORING THE RETURN OF THE POLECAT TO THE ‘FAR EAST’ JOHNNY BIRKS After an absence of at least a hundred years, the polecat Mustela putorius is poised to recolonize East Anglia from its historical stronghold in the west. This is a hugely exciting prospect in nature conservation terms; but there are challenges for both the polecats and we humans as we get to know each other again.

Church wardens’ accounts indicate that, in the Middle Ages, the unfortunate polecat suffered heavier persecution than any other British mammal, with huge numbers trapped and killed all over Britain. In Shakespearean times its reputation was so awful that the word ‘polecat’ was used as a form of abuse (and it still is occasionally today, as a search of Hansard will confirm). There are three reasons why the polecat was so hated by our ancestors: it tends to favour lowland habitats and so would have foraged around farms and cottages where predation upon poultry was common in the days before the invention of strong wire mesh; it defends itself by emitting a pungent stink when cornered or frightened; and it has a striking facial mask so that any unpleasant encounters were memorable to the human participant. Finally, in the 1800s, the rise of organised game shooting and the game-keeping profession provided a more sustained incentive to eradicate polecats, with the result that most counties had lost the species by the time the First World War broke out.

Evidence from the Victoria County Histories suggests that polecats became extinct in Essex around 1860 and in Cambridgeshire, Norfolk and Suffolk in the period 1900–1910. Despite remaining quite widespread beyond 1850, by 1915 the species had been removed from most of mainland Britain, surviving mainly in a small, mountainous area of mid-Wales where the human population and associated levels of trapping were lower. This relatively swift eradication of a native mammal from such a wide area was entirely due to culling by humans. Having dropped off our county mammal lists a hundred or more years ago, the polecat’s prolonged absence over most of Britain means that it also faded out of our culture; this was perhaps a good thing given its terrible historical reputation. Might we be more tolerant if the polecat gets a second chance?

The onset of the First World War in 1914 brought some respite that quite probably saved the polecat (and some other predators) from complete extinction in Britain, because many men involved in predator removal left to fight in the trenches across the English Channel. Subsequently trapping pressure never reached the same intensity in Britain, so the polecat population was able to recover slowly from its far Welsh stronghold.

The polecat is a generalist predator that is able to thrive in a wide range of habitats from lowland farmland to the urban fringe. Like the resurgent buzzard Buteo buteo, its more detectable avian counterpart, the polecat’s eastward recovery through the late twentieth century was driven by the combination of reduced persecution and the post-Myxomatosis recovery numbers of in wild rabbits Oryctolagus cuniculus – a favoured prey. Indeed healthy populations of rabbits provide the bulk of both food and resting sites for polecats - studies by The Vincent Wildlife Trust (VWT) in the Trans. Suffolk Nat. Soc. 51 (2015)

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1990s revealed that wild rabbits made up 85% of the polecat’s diet in England, and rabbit burrows comprised 80% of daytime resting sites used by radio-tracked polecats on lowland farmland. On the downside, winter polecat activity involves frequent hunting of brown rats Rattus norvegicus in farmyards and, like barn owls Tyto alba, polecats are vulnerable to the secondary effects of modern rodenticides ingested accidentally as they consume their ratty prey. Studies suggest that up to 40% of polecats may be sub-lethally affected by a cocktail of rodenticides by the end of winter, with an unknown proportion lethally affected.

So how is the polecat’s recovery progressing and what are the chances of populations re-establishing in East Anglia? The pattern of polecat recovery has been tracked since the early 1990s by a series of volunteer-based recording exercises run by the VWT at approximately ten-year intervals. These have revealed a slow expansion from the Welsh border, helped at times by unofficial translocations of polecats to places beyond the eastward advancing front, such as to Hertfordshire in the early 1980s. The Hertfordshire release probably explains the records of polecats in North Essex from 1999 onwards. By 2006, when the VWT’s second distribution survey ended, polecats were apparently re-established in all English midland counties as far east as, and including, Leicestershire, Northamptonshire, Bedfordshire and Hertfordshire. Further east into East Anglia, polecats were recorded occasionally, but in numbers too low to suggest that established populations existed at the time. The VWT’s latest survey (spanning 2014 and 2015) has received records of polecats from Cambridgeshire, Suffolk and Essex, suggesting that the eastward spread has continued. However, there are complications for recorders that we have to explore: the first of these I call the ‘ferret factor’.

The domestic ferret Mustela furo is descended from our species of polecat, following domestication somewhere in southern Europe about 2000 years ago.

Domestication involved selective breeding to remove most of the polecat’s hunting and survival skills in order to create a working animal, the ferret, which was relatively docile and ineffective at catching its quarry – usually rabbits – which bolted from their burrows to be shot, netted or caught by dogs. Despite the man-made changes in behaviour and appearance (historically ferrets were mainly albino animals), ferrets remain genetically very similar to wild polecats; the two are fully inter-fertile and interbreed readily if given the opportunity; although taxonomists have given them separate scientific names, they are so closely related that there is a case for regarding the ferret simply as a domesticated form of the polecat, rather than as a separate species.

The recording problems arise because, for many years, ferrets have been released or have escaped into the wild in Britain to interbreed with wild polecats, creating a variety of so-called ‘hybrids’ that are sometimes called polecat-ferrets, and adding to the diversity in pelage colour of the population of wild-living polecat-like animals. A lack of familiarity among naturalists with the appearance of true polecats and associated uncertainties about how to distinguish true polecats from polecat-ferrets undermines our efforts to record the distribution of true polecats; there are also legal

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issues because the true polecat receives some protection through its listing on Schedule 6 of the Wildlife and Countryside Act 1981, whereas the polecat-ferret does not.

There are geographical variations in the frequency of occurrence of polecat-ferrets among the polecat population in Britain: within Wales, the English border counties and parts of the English midlands they are relatively scarce; whilst at the fringes of the polecat’s expanding range in England (including its eastward edge close to East Anglia), and in translocated outlier populations, they tend to be more common. This is partly because, towards the fringes of the polecat’s range, dispersing polecats may find themselves in areas where the only mating opportunities are offered by escaped or feral ferrets. However, there is another reason behind the geographical pattern: because of the process of domestication, ferrets are inherently poorer at surviving in the wild than true polecats; so they are bound to fail when competing for resources in areas where true polecats (or other carnivores) are well-established. It follows that polecat-ferrets have a better chance of survival in the wild where true polecats are absent or not yet well-established; this is why feral ferrets thrive best on off-shore islands where prey (such as rabbits and seabirds) is abundant and native predators are scare or absent.

A further complication arises as a consequence of a recent genetic analysis of British polecats and polecat-ferrets by Mafalda Costa of Cardiff University. She found that about 30% of polecat-like animals beyond Wales and the English border counties had evidence of ferret in their genetic make-up, confirming the assumptions of a long history of ‘hybridisation’. More worryingly, she found that there was a poor match between an animal’s genotype (what its DNA tells us about its origins) and its phenotype (what it looks like); so, among the polecat population in the English midlands, there are animals that look like true polecats but have evidence of ferret in their DNA and vice versa. This means that, when making judgements about the conservation value of animals, we should not be too dismissive of wild polecat-ferrets because they may contain valuable polecat genes.

The pragmatic way to deal with this situation is to accept that, as a consequence of past human interference via the domestication process, members of our wild polecat populations are a little more variable in appearance than they would have been otherwise. The good news is that, despite the widespread occurrence of ferret genes in English polecats, the polecat phenotype appears to be dominant and is likely to assert itself in the long term in the wild population (although monitoring is essential in order to keep track of this effect over time). Whilst wild polecat-ferrets may have some conservation value as suggested above, we should focus primarily on recording and conserving animals that have the true polecat phenotype.

The extent to which polecats can recolonize East Anglia depends upon the balance between habitat quality and mortality factors: the wetlands, forests, heaths and farmland of the region should support thriving polecat populations, especially where rabbits are common; but will they withstand the levels of anthropogenic mortality arising from the main modern threats of spring traps, rodenticides and busy roads?

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And can we expect greater human tolerance towards polecats and a kinder image for the species than our ancestors bestowed upon it? The next few decades should enable us to answer these questions.

Naturalists can help to track the polecat’s re-establishment in East Anglia by contributing records to the VWT’s current national polecat survey. The VWT is keen to receive carcasses or photographs of any polecat-like animals. http://www.vwt.org.uk/our-work/projects/national-polecat-survey.

Dr Johnny Birks Swift Ecology, Glen Cottage, Lower Dingle, West Malvern, Worcestershire WR14 4BQ johnny.birks@swiftecology.co.uk

Update on Polecats in Suffolk In the last two years, there have been increased numbers of sightings of polecat-type mammals, either as road casualties, live-trapped ones or sightings of tame animals in daylight. Identification has been assisted by photographs, which have also been sent to Lizzie Croose, The Mustelid Conservation Officer at Vincent Wildlife Trust (VWT), who has been verifying the sightings. VWT is coordinating the National Polecat Survey 2014–15, which was last undertaken 2004–06 (see url above).

Separating out whether a specimen is a true polecat or a polecat ferret hybrid can be difficult. A well-marked facial mask with the black on the face reaching the nose and lack of white fur on the body are characteristics of a true polecat, but it is not always clear-cut due to hybridisation. Photographs are vital to enable verification to take place.

In both 2014 and 2015 there were at least a dozen records of true polecat (see map opposite). Johnny Birks’ talk at the Mammal Conference in November 2014 mentioned a population of ‘true’ polecat in north Essex which was spreading northwards into Suffolk. Not surprisingly, a cluster of records occurs around Bures St Mary, Leavenheath, Assington and Newton (see Plate 1). However, there have been some additional records of ‘true’ polecats elsewhere in the county which don’t seem to follow any pattern of colonisation. In 2014, there were records at Wickhambrook and Bardwell and in 2015, a record at Woodbridge, two records at Lackford and another just over the border in Norfolk at South Lopham near Redgrave. The latter was caught in a rabbit trap on 17 November 2014 and released. Another polecat recovered at Redgrave as a road casualty on 14 April 2015 was originally thought to be the same animal caught at South Lopham, but comparison of the facial mask indicated this was a different animal.

Due to the presence of hybrid polecat-ferrets in Suffolk, the pattern of recolonization of polecats into Suffolk is always going to be harder to chart. However, their spread should continue to be monitored by sending in records and photographs so that hopefully, we can get a better picture of their recovery to the county.

Simone Bullion Suffolk Mammal Recorder

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N. Oliver

Suffolk records of Polecat and Polecat-ferret from 2014 and 2015.

Plate 1: True Polecat Mustela putorius trapped at Newton, November 2015. (p. 4).

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