Polecats Are Coming Back!
Dr Johnny Birks
This is the overwhelming conclusion of a report published recently by The Vincent Wildlife Trust entitled The Distribution and Status of the Polecat Mustela putorius in Britain in the 1990s, by Johnny Birks and Andrew Kitchener. Covering many aspects of the ecology and conservation of wild polecats in Britain today, the report includes a review of previous distribution surveys, the findings of a new survey, development of a method to monitor variations in polecat abundance based on live-trapping by volunteers, and a description of polecat ecology on lowland farmland in England. There is much to interest the ferret-keeper in the report, including a whole chapter devoted to studies of the genetic and ecological relationships between polecats and ferrets in Britain.
The 1990s polecat distribution survey involved collection of hundreds of polecat corpses, mostly recovered as road casualties. These were processed by the National Museums of Scotland where, among many valuable studies, work on the polecat/ferret relationship was carried out. Skins were scored and skulls measured from polecats and ferrets from many parts of Britain, and compared with those from 'pure' Welsh animals to determine where else true polecats still survived. Despite increasing evidence of hybridisation with ferrets as one moved east through the polecat's range, true Welsh-type animals were found throughout Wales, in the English Midlands, and in populations derived from reintroductions. True polecats are now re-established in the Midlands by natural spread at least as far east as a line through Macclesfield, Northampton and Oxford, and through reintroductions to Argyll, Cumbria, the Chilterns and parts of Hampshire and Wiltshire in central southern England.
Studies of mitochondrial DNA at the University of Leeds revealed two geographically distinct lineages in British polecats and feral ferrets which probably reflect the past history of hybridisation. However, this work also showed just how closely related the two forms are, adding weight to the view that the ferret is simply a domesticated variant of the wild polecat. Domestication in ferrets involved a considerable weakening of the predatory and survival skills found in wild polecats. As a consequence the ferret is severely disadvantaged in the feral state, so there is likely to be selection for the polecat 'type' in all wild populations. This is expected to limit the damaging effects, in terms of polecat conservation, of hybridisation with ferrets.
To improve understanding of the polecat's recovery, a monitoring exercise based on live-trapping by volunteers was developed and tested. 136 1km squares of the Ordnance Survey grid were each live-trapped for seven nights. Significant regional variations in trapping success were recorded, with squares near to the species' historical stronghold more likely to catch polecats. The trapping data revealed a positive association with rabbit abundance, and a negative association with areas of high road density. It seems likely that polecat mortality on Britain's roads may be high enough in some areas to cause population effects; this may explain why the species has still not re-established itself fully in the valleys of South Wales.
The apparent link between polecats and rabbits was backed up by diet and radio-tracking studies. Analysis of stomach contents of road casualty animals showed that rabbits comprised 85% of the bulk of prey remains. In the English Midlands radio-tagged polecats spent half their time in rabbit warrens hunting the occupants and sleeping. Warrens comprised 80% of all polecat resting sites identified. So, as the polecat continues to re-establish itself, ferreters are increasingly likely to encounter the wild relatives of their own animals when out rabbiting! In winter, farmyards were the habitat most preferred by polecats. Polecats visited them to prey upon rodents, leading to potential contamination with anticoagulant rodenticides. The VWT is currently studying the extent of this problem in collaboration with the Institute of Terrestrial Ecology.
The VWT report makes recommendations for research and action to promote polecat conservation. It recognises that the species is spreading from an upland, western refuge with relatively low human activity towards the intensively farmed lowlands where negative pressures are much greater. Areas of concern include the effects of road casualties, rodenticide poisoning, deliberate and accidental persecution, and habitat degradation. Maintaining rabbit populations is regarded as important, especially on intensive farmland where alternative prey are scarce.
The VWT Polecat Report is available from The Vincent Wildlife Trust, 10 Lovat Lane, London EC3R 8DN, price £6.00 to include post and packaging.
(First published April 1999)