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WILDLIFE OF NORTHERN ENGLAND

Mammal status UK part 18 Mink and Polecat. Text on this page courtesy of Natural England.

Image courtesy of Malene Thyssen CC BY-SA 3.0 license.

Polecat Mustela putorius.  Preferred habitat.

The polecat is a generalist species in terms of both habitat selection and diet. It tends to prefer woodland edge, farm buildings and field boundaries, and to avoid open fields (Birks and Kitchener, 2008; Birks, 2015). High road casualty rates may prevent the establishment of populations in urban and suburban areas, although it is occasionally found in these places (Birks and Kitchener, 1999a). Unlike its counterparts in mainland Europe, the polecat in Britain does not show a preference for riparian habitats, possibly to avoid competition with the American mink. High rabbit abundance throughout the species’ range provides an alternative food source outside of riparian habitats. A high proportion of activity is associated with rabbit warrens, and these sites are also frequently used for denning (Birks, 2015). The polecat is less strongly territorial than other small mustelids: territories can be vacated voluntarily and are not necessarily refilled (Blandford, 1986.

Status

Status . Native.
Conservation status.
 
• IUCN (GB: LC; England: [LC]; Scotland: [EN]; Wales: [LC]; Global: LC). • National Conservation Status (Article 17 overall assessment 2013. UK: Favourable; England: Favourable; Scotland: Unknown; Wales: Favourable).

Distribution and population.

Image courtesy of Peter Trimming {storm} CC BY-SA 2.0 License.Storm the polecat.jpg

 In Scotland, records of true polecats are very sparse (see the ‘Critique’ section below). The highlighted areas on the distribution map below are therefore most likely to represent occasional individuals, or misidentified ferret-polecat hybrids, rather than an established population of true polecats.

 Since polecats are generalists and can be found in most habitat types, population density estimates in the literature are not habitat-specific. To permit comparison to previous reports (and in the absence of any other relevant data), population sizes were therefore calculated by multiplying the population density by the total area of the species’ distribution. Given that polecats are unlikely to occupy urban areas (Birks, 2015), areas classed as urban in the LCM2007 data were removed from the total distribution area using ArcGIS 10.2.2.

 Occupancy data are taken from Birks & Kitchener (1999). In the original reference, occupancy is incorporated within the population density estimates: mean density was calculated as 0.85km-2 (95%CI = 0.69km-2-1.01km-2), where 52.3% of 1km squares were occupied (ranging from 56.1% in the centre of the range to 48.5% on the edge).

 All records from Scotland are thought to be occasional records and/or misidentified ferretpolecat hybrids, so no population size was calculated for this country.

 Four relevant papers were identified by the literature search. One paper reported prebreeding population density estimates and percentage occupancy, one contained estimates of total population size, and two gave details of distribution.

Population size estimates for polecats were based on 136 individual density estimates from one study. These density estimates are area- rather than habitat-specific, so it is not possible to assess the proportion of the population size or geographical range accounted for by each habitat.

 Density estimates and percentage occupancy values in Birks and Kitchener (1999b) were taken from areas throughout the species’ range in England and Wales. In Scotland, fewer than 85% of records received by the Vincent Wildlife Trust during 2014-2015 were classified as true polecats, as opposed to polecat-ferret hybrids or ferrets (Croose, 2016), and there were fewer than five verified records in the eastern fringe of the distribution. In contrast, most of the species’ range in England contained 85% to 95% true-polecat records, and in Wales the value was >95%. It is therefore possible that the current estimate overlooks a small population of polecats in Scotland — Birks and Kitchener (1999b) estimated the population in Scotland to be between 345 and 483 — but this is unlikely to have a major impact on the total figures for Great Britain.

 Density estimates are based on the number of sightings per survey. Therefore, they provide a minimum number, rather than a modelled estimate of density. Surveys were conducted between 1997 and 1999, so it would be beneficial to reassess population densities across the species’ range, including recently recolonised region.

Changes through time.

Population size was estimated to be 15,000 by Harris et al. (1995), comprised of 2,500 polecats in England and 12,500 in Wales. Population sizes were estimated using more than one method, including applying high (1km-2) and low (0.1km-2) densities across the species’ range. These density estimates resulted in population sizes ranging from approximately 2,000 to 21,000, and are comparable methodologically to the current review. Population sizes have increased significantly between the two reviews. This appears to be entirely driven by an increase in range, although more recent density data would help to verify this conclusion.

Population trends. Increase. Range ,increase, habitat stable. 

Mink. Neovison vison. 

American Mink Neovison vison. Image courtesy of Pdrejinders CC BY-SA 3.0 license.American Mink.jpg

Mink, preferred habitat.

The American mink became established in Britain following escapes or releases from fur farms in the early 20th century (Macdonald and Harrington, 2003). It is a generalist predator and shows a strong preference for riparian habitats, particularly those with abundant cover, where it feeds on a wide range of prey, including waterfowl, fish and water voles. High population densities are also found in undisturbed rocky coastal areas. Estuaries, urban canals, and habitats away from water may, also, provide sufficient habitat if cover and prey, such as rabbits, are available (Dunstone and Macdonald, 2008). In the Upper Thames region, mink were found to favour areas with tree and scrub cover and to avoid open areas, particularly farmland (Yamaguchi et al., 2003). There is inter-specific competition with the otter: declines in mink signs, and a shift towards a more terrestrial diet and diurnal rather than nocturnal behaviour, have been noted to correlate with the resurgence of otter populations (Bonesi and Macdonald, 2004; Bonesi et al., 2006; McDonald et al., 2007; Harrington et al., 2009)

status

Native -non native

Conservation status - • IUCN Red List (GB: n/a; England: n/a; Scotland: n/a; Wales: n/a; Global: LC). • This species has not been assessed for Article 17 of the EU Habitats Directive.


 • IUCN Red List (GB: n/a; England: n/a; Scotland: n/a; Wales: n/a; Global: LC). • This species has not been assessed for Article 17 of the EU Habitats Directive.

 • IUCN Red List (GB: n/a; England: n/a; Scotland: n/a; Wales: n/a; Global: LC). • This species has not been assessed for Article 17 of the EU Habitats Directive.

Population and distribution.

A distribution map is presented in Figure 8.9a. Gaps in the species’ distribution in the Scottish Borders and Argyll are likely to represent areas lacking survey effort, rather than true absences. The species is known to be present in all areas of mainland Scotland except for the far north (see Fraser et al., 2015b; Gaywood et al., 2016).

 The length of riparian habitat for Scotland, England and Wales was taken from Table 4 in the previous Review of British Mammals (Harris et al., 1995) and multiplied by the percentage of each country included in the species’ distribution to give the length of available riparian habitat. Percentage occupancy was taken from Bonesi et al. (2006), using the percentage of sites (n=3188) within 32 50 x 50km squares surveyed during the National Otter Survey of England. The length of suitable coastline was taken from Table 10.3 in Jefferies et al. (2003). As there have been no records of mink in the Outer Hebrides since 1995, these islands were not included. The coastlines of Arran, Skye and Mull were adjusted using the percentage occupancy for Arran (Jefferies et al., 2003)

 Eight papers were identified by the literature search. One reported a pre-breeding population density estimate for rivers, and two gave pre-breeding density estimates for coastal populations. One paper contained home range estimates (Males = 1.5 km, females = 1.09 km; Dunstone and Birks, 1985), and one gave presence and occupancy data. The remaining papers contain post-breeding or relative measures of population density. Percentage occupancy was estimated to be 74% by Bonesi et al. (2006) for riparian populations, whilst occupancy for coastal populations was taken from Jefferies et al. (2003): 5.97% in England; 15.15% in the Scottish mainland; 37.5% in Arran (applied to all currently occupied Scottish islands); and 3.57% in Wale.

 Population size in riparian habitats was estimated from a single density estimate. Coastal populations, which account for only 2% of the total population size, were based on two density estimates. The small contribution of coastal areas to the overall population is, in part, owing to the length of available coastline, which is substantially shorter than the length of available riparian habitat. However, there is also a large difference in the percentage occupancy values for the two habitat types. The most recent values for percentage occupancy were used in each case, with the value for coastlines taken from Jefferies et al. (2003) and riparian habitats from Bonesi et al. (2006). Occupancy of riparian habitats was also provided in Jefferies et al (2003) and, as for coastlines, was calculated as the percentage of 10 x 10km squares positive for mink within Water Authority Regions, or longitudinal sections of differing river length and 100km width. In contrast, Bonesi et al. (2006) used the percentage of occupied sites within alternate 50km x 50km squares. Both Jefferies et al. (2003) and Bonesi et al. (2006) reported the same declining temporal trend in occupancy relative to the same measures of occupancy in previous years, but the absolute occupancy values are not comparable between studies. For the older survey of riparian habitats (Jefferies et al., 2003), the values were 13.42% in England, 10.69% in Scotland and 3.74% in Wales. If these values are used in place of those from Bonesi et al. (2006), the population size estimate is reduced considerably to 20,300 in Britain, comprised of 11,600 in England, 8,000 in Scotland and 700 in Wales.

Image courtesy of Ryzhkov Sergey CC BY-SA 4.0 licenseFile:American mink.jpg

Changes through time.

The population size estimated by Harris et al. (1995) was at least 110,000 individuals, with 46,750 in England, 52,250 in mainland Scotland and 9,750 in Wales. The authors stated, however, that more information was needed on the coastal and island population to improve the reliability of the estimate, and suggested that the percentage of occupied habitat (which was based on data from the English National Otter Survey and expert opinion) was likely to be underestimated. The same problems persist in the current review, and so the identification of temporal trends has been limited to comparisons within survey types, i.e., The Water Vole and Mink Survey of Britain (Jefferies, 2003), or The National Otter Survey dataset (see Bonesi et al., 2006).

 was based on data from the English National Otter Survey and expert opinion) was likely to be underestimated. The same problems persist in the current review, and so the identification of temporal trends has been limited to comparisons within survey types, i.e., The Water Vole and Mink Survey of Britain (Jefferies, 2003), or The National Otter Survey dataset (see Bonesi et al., 2006). The GWCT National Gamebag Census for mink suggests a decrease of 41% (95%CI = 49%-33%) in culling rates between 1995 and 2009. However, this trend is not adjusted for effort, which may also vary over time.

Future trends. Population possible decline due to culling.

Habitat- Stable 

Range stable. 

 

 

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