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WILDLIFE OF NORTHERN ENGLAND

Mammal status. UK, part 3 Hedgehog. Text courtesy of Natural England .org

Image courtesy of Marek Szczepanek CC BY-SA 3.0 license.Erinaceus europaeus (Marek Szczepanek).jpg

Habitat preference.

The hedgehog is found in most habitats, although it is increasingly associated with urban areas, and is often observed in gardens and amenity grasslands. Because it is a mobile, generalist species, road fatalities are fairly common, but these have declined over recent decades, providing some indication of a declining population (Wembridge et al., 2016b). Hedgehogs in rural villages have recently been shown to have small home ranges compared with other habitats, presumably because of greater foraging resource and nest site availability (Pettett et al., 2017). Density is higher in areas with amenity grassland compared with pasture (Micol et al., 1994; Young et al., 2006; Parrott et al., 2014); key prey items, including earthworms, ground beetles and tipulid larvae, are important in determining their distribution. The presence, and abundance, of badgers — one of the few natural predators of hedgehogs — is inversely linked with hedgehog distribution patterns (Doncaster, 1994; Young et al., 2006; Parrott et al., 2014; Trewby et al., 2014).

Status

Native.

Conservation status.

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

Habitat size and population.

England 123,000 Area of suitable habitat 2km2  population size [320,000]

 Scotland 47,100   Area of suitable habitat  2km 2 population size.[145,000]

 Wales 18,800  Area of suitable habitat  x 2km 2 Population size. [56,800]

 Britain 189,000 Area of suitable habitat  2km2 Population size. [522,000]

Distribution UK

Gaps in the species’ distribution in Scotland are likely to represent areas lacking survey effort, rather than true absences. Further survey effort is recommended in these areas to increase confidence in the current distribution.

 

 Hedgehog occurrence has been monitored by a number of nationwide surveys, where percentage occupancy is the percentage of unique locations where hedgehogs or field signs were observed. Several of these studies have measured hedgehog occurrence in gardens and amenity grassland (Micol et al., 1994; Roos et al., 2012; Parrott et al., 2014). The results of Living with Mammals (PTES), Garden Birdwatch (BTO), Make Your Nature Count (The Royal Society for the Protection of Birds) and HogWatch (PTES) are summarised by Roos et al. (2012). The mean percentage occupancy for the most recent year (per country where available) from these surveys, and from Micol et al. (1994) and Parrott et al. (2014), was used as percentage occupancy for urban and gardens. The HogWatch data came from 2006, as very few responses were received in subsequent years.

 

 Percentage occupancy was also available for some other habitats, including pastoral land, grassland, woodland, arable land, roads and along waterways. However, most of the surveys incorporate a variety of habitats, rather than providing habitat-specific occupancy values. Data from a range of studies conducted since the Harris et al. (1995) review were summarised by Roos et al. (2012). Mean percentage occupancy for the most recent year (per country where available) from these surveys, and from Hof and Bright (2012) and Parrott et al. (2014), was used as percentage occupancy for all other habitats.

 

 Ten papers were returned from the literature search in total. Two papers contained prebreeding population density estimates, although one paper only contained density estimates for blackland (peatland) and machair habitats that are specific to the north west of Scotland and the offshore islands (Jackson, 2007), and so was not included in the analysis. Three papers contained measures of percentage occupancy, two contained post-breeding density estimates, one contained relative abundance measures, and two presented habitat suitability measures.


 Hedgehog occurrence has been monitored by a number of nationwide surveys, where percentage occupancy is the percentage of unique locations where hedgehogs or field signs were observed. Several of these studies have measured hedgehog occurrence in gardens and amenity grassland (Micol et al., 1994; Roos et al., 2012; Parrott et al., 2014). The results of Living with Mammals (PTES), Garden Birdwatch (BTO), Make Your Nature Count (The Royal Society for the Protection of Birds) and HogWatch (PTES) are summarised by Roos et al. (2012). The mean percentage occupancy for the most recent year (per country where available) from these surveys, and from Micol et al. (1994) and Parrott et al. (2014), was used as percentage occupancy for urban and gardens. The HogWatch data came from 2006, as very few responses were received in subsequent years.

 Hedgehog occurrence has been monitored by a number of nationwide surveys, where percentage occupancy is the percentage of unique locations where hedgehogs or field signs were observed. Several of these studies have measured hedgehog occurrence in gardens and amenity grassland (Micol et al., 1994; Roos et al., 2012; Parrott et al., 2014). The results of Living with Mammals (PTES), Garden Birdwatch (BTO), Make Your Nature Count (The Royal Society for the Protection of Birds) and HogWatch (PTES) are summarised by Roos et al. (2012). The mean percentage occupancy for the most recent year (per country where available) from these surveys, and from Micol et al. (1994) and Parrott et al. (2014), was used as percentage occupancy for urban and gardens. The HogWatch data came from 2006, as very few responses were received in subsequent years.

 Hedgehog occurrence has been monitored by a number of nationwide surveys, where percentage occupancy is the percentage of unique locations where hedgehogs or field signs were observed. Several of these studies have measured hedgehog occurrence in gardens and amenity grassland (Micol et al., 1994; Roos et al., 2012; Parrott et al., 2014). The results of Living with Mammals (PTES), Garden Birdwatch (BTO), Make Your Nature Count (The Royal Society for the Protection of Birds) and HogWatch (PTES) are summarised by Roos et al. (2012). The mean percentage occupancy for the most recent year (per country where available) from these surveys, and from Micol et al. (1994) and Parrott et al. (2014), was used as percentage occupancy for urban and gardens. The HogWatch data came from 2006, as very few responses were received in subsequent years.

Image courtesy of Jorg Hempel CC BY-SA 2.0 license de.Erinaceus europaeus LC0119.jpg

Very few recent density estimates were found for hedgehogs: data were available only for improved grasslands and urban areas (Parrott et al., 2014). Median density estimates for both of these habitats are supported by four individual density estimates from one study. Despite improved grassland being the most common habitat across the species’ distribution the population size is largely determined by density estimates in unimproved grassland and broadleaved woodland. These estimates, which are based on Harris et al. (1995), are substantially higher than for other habitats. However, the density estimates presented in Harris et al. (1995) for improved grasslands and urban areas (5km-2 and 10km-2) are an order of magnitude greater than more recent estimates for these habitats, and were largely based on the expert opinion expressed in Burton (1969). It is therefore concluded that the estimates from Parrott et al. (2014) are more reliable.

 As the current estimate is largely based on density estimates from Harris et al. (1995), the reason for a reduction in population size is likely to be the use of percentage occupancy data, rather than differences in population density, as occupancy data were not used in Harris et al. (1995). Percentage occupancy was taken from a large number of sources (see Micol et al., 1994; Hof and Bright, 2012; Roos et al., 2012; Parrott et al., 2014), although a mean value was used for most habitats. Percentage occupancy ranged from 0% to 81% across all studies, in all parts of Great Britain, so stratification by area, with habitat-specific occupancy data, would provide a significant improvement to the current analysis.

 

 If we assume the estimate provided in Harris et al. (1995) to be the best estimate available for that time period, then applying the decline in relative abundance of hedgehogs estimated by Roos et al. (2012) from citizen-science surveys (40% every 10 years) would result in a total population size of 560,000 in Britain, which is close to our estimate. This extrapolation is, however, subject to uncertainty in the original population size as well as in the trend data. The species’ range has remained relatively stable since 1993 (Arnold, 1993), suggesting that declines in population size are owing to reduced density or occupancy. Inferences about density declines are supported by the relative lower density estimates in Parrott et al. (2014) compared with those from studies in continental Europe, which are between 2km-2 and 300km-2, depending on habitat type (Huijser and Bergers, 2000). The recent density estimates are also lower than those from Harris et al. (1995), although the latter were largely based on expert opinion rather than empirical data. As well as suggesting that hedgehog

 density is highly variable, these figures highlight the need for more empirical data on the population density and occupancy of hedgehogs to improve confidence in the current population density and subsequent size estimates. To reflect the uncertainty arising from the use of expert opinion in Harris et al. (1995), the density estimates classified as having been derived from a restricted range.

Changes through time.

Harris et al. (1995) provided an estimate of 1,555,000 hedgehogs in Britain. The current estimate is substantially lower (-67%). Nationally, there are changes between the two reviews in the estimated availability of key habitats (broadleaved woodland, improved and unimproved grassland, and arable land), generated by a combination of true change and methodological differences, irrespective of any range change.     Adjusting the results to reflect more probable temporal changes in the composition of the British landscape — using differences between the 1990 and 2007 Countryside Surveys (Carey et al., 2008) — generates a population size of 423,000, which is a 73% decrease.

 

 Even greater declines would be implied were the estimates based entirely on the density data given by Parrott et al. (Parrott et al., 2014). It is therefore possible that population size has declined further than estimated here, but all current estimates are very uncertain.

 The relative abundance of hedgehogs has been monitored by several organisations in the UK over the last 25 years. These studies, which used different methodologies and were of varying duration, were reviewed by Roos et al. (2012). There was considerable inter-annual variation within each study, and also variation between them — annual declines ranged from a mean of 1.8% to 10.7% — but there was consistency in the direction of the effect. The authors inferred a decline in relative abundance of 40% in 10 years. However, the scale of this decline contrasts with another study which used non-systematic occupancy records from Biological Records Centres and adjusted for survey effort (Hof and Bright, 2016). Here, a decline of between 5.0% and 7.5% was found for England over a 40- year period, which would mean a maximum decline of 1.9% over 10 years.

The population trend is one of decline in all countries. 

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