The Hedgehog Erinaceus europaeus has an unmistakable appearance with its back and flanks covered with around 6,000 sharp brown spines and its face and underside with coarse grey-brown fur. Depending on age, adult body length can range from 20-30cm, with weight reaching up to two kg in the autumn when hedgehogs are at their heaviest. The average life expectancy in the wild is around two to three years with over half dying in their first year, although some can live for five years or more.
Hedgehogs are nocturnal and largely solitary, with the exception of mothers with young. Litters of four to five hoglets are born typically between May and September with young born later often dying as they are too small to survive hibernation, at the start of which juveniles need to be at least 450 g to ensure fat deposition is adequate. Hedgehogs hibernate from November to March to conserve energy, although the length of this period is weather dependent. During winter they wake on average once a week in order to forage, during which body temperature is raised from 5°C to 30°C, a process taking several hours. Once active in the spring they may re-enter hibernation during a cold snap.
Diet consists predominantly of ground-dwelling invertebrates including earthworms, beetles, caterpillars and slugs, with approximately 70 g of food being consumed per night, during which Hedgehogs will travel one to two km over home ranges of 10-30 ha. Hedgehogs are not territorial and radio-tracking studies have shown that there can be considerable overlap between foraging areas. During the day they rest in nests lined with leaves, grass and twigs, although if the climate is warm enough they may sleep under wood piles, pine needles or bushes and foliage. Hedgehogs use many day nests and each can be frequented by many individuals.
Hedgehogs are present throughout the UK, with the exception of some Scottish islands, in almost all lowland habitats where there is sufficient nesting cover. They are particularly abundant where woodland edges and hedgerows are in close proximity to grassland. With the decline of these traditional habitats, parks, gardens and brownfield sites in urban areas are becoming increasingly important.
Although there has never been a full national survey, it is generally accepted that the UK population has been in significant decline for a considerable time. Estimated to number around 30 million in the 1950s, a 1995 Joint Nature Conservation Committee (JNCC) study based on hedgehog densities per habitat type indicated that the population had fallen to 1.5 million (Harris et al, 1995).
More recent surveys in urban and rural areas show a continuing decline with a 2011 report suggesting that, at a conservative estimate, a quarter of the population has been lost during the last 10 years (Wembridge, 2011). Hedgehog populations can fluctuate from year to year due to the weather and the subsequent availability of prey and also whether conditions are suitable to allow a second litter to be raised. Nevertheless, nationally the survey evidence indicates a continual average decrease of several per cent per year. The current population is unknown due to the inherent difficulties in surveying a nocturnal creature.
This decline can be attributed to several factors, all with varying degrees of contribution. Land use change resulting in the spread of urban landscapes and a move towards more intensive agriculture has led to the loss and fragmentation of suitable habitat. With the development of larger, arable fields to increase agricultural productivity, hedgerows, rough field edges and permanent grassland have been lost, limiting the availability of nesting sites and reducing the Hedgehog carrying capacity. Within urban areas tidier, more sterile gardens with impenetrable boundaries have removed hibernation sites and restricted the extent of wildlife corridors for this mobile species. Small populations have become increasingly isolated and vulnerable to local extinction. In addition, the use of agricultural and garden pesticides has reduced the insect food supply and may also result in secondary poisoning through the food chain.
As there are now fewer areas for Hedgehogs to take refuge in, it is thought that Badgers Meles meles are presenting an increasing problem. Although Badgers are a natural predator of Hedgehogs, usually the two can co-exist where the habitat provides sufficient cover, for example in Gosforth Park Nature Reserve in Newcastle upon Tyne. Studies in suburban habitats indicate that the probability of Hedgehog occurrence declines towards zero in areas of high Badger density, with Badger presence limiting the ability of hedgehogs to move between patches of habitat (Young et al, 2006). It is not known as to what extent this is an issue in the North East where there are few populations of urban Badgers.
Having spines reduces the requirement for Hedgehogs to run for cover, a habit which has not aided Hedgehogs in the age of the motor vehicle. However it has been suggested that overall roads may not represent a major threat to the population (Morris, 2006), although they can be a locally important cause of mortality and therefore a key technique for measuring Hedgehog numbers. Since the first national survey in 2001 a decline in road casualty records despite an increase in traffic reliably indicates a downward trend in the population (People’s Trust for Endangered Species, 2011).
Within the North East, records indicate that the population is concentrated in lowland areas including urban gardens, away from the less favoured upland habitats such as heather moors, which tend to have fewer areas for nesting and a decreased number and variety of invertebrates. However, Hedgehogs are occasionally found on higher ground with recent sightings in the College and Harthope Valleys, Northumberland. A further record of note is from 2009 when a Hedgehog was sighted foraging on Holy Island, which is linked to the Northumberland mainland at low tide by a causeway. A large number of Hedgehog records have been generated from public surveys including a Durham BAP survey in 2006-2007, which will skew the results towards human habitations. Road kill sightings have been significant and are noticeably important in determining the extent of Hedgehog distribution but these also skew the distribution of records, though some trends still emerge. For example Ian Bond (pers. comm., 2012) has noted that in the Tees Valley, Hedgehog road kills are concentrated on the perimeters of villages or hamlets and are very rarely encountered on stretches of road through the open countryside between them. This could suggest that the wider countryside may currently be of less value for Hedgehogs.
Written by Francesca Leslie (last updated Nov 12)