European hedgehog

Description

Erinaceus europaeus has a generalised body structure with unspecialised limb girdles. The animal appears brownish with most of its body covered by up to 6,000 brown and white spines. Length of head and body is ~160 mm (6.3 in) at weaning, increasing to 260 mm (10 in) or more in large adults. This species has an extremely short tail as an almost vestigial feature, typically 20 to 30 mm (0.79 to 1.18 in). Weight increases from around 120 g (4.2 oz) at weaning to > 1,100 g (2.4 lb) in adulthood. The maximum recorded weight is 2000 g (4.4 lb), though few wild specimens exceed 1,600 g (3.5 lb) even in autumn. Adult summer weight is typically somewhat less than in autumn, with an average of around 800 g (1.8 lb) and adult weights commonly as low as 500 g (1.1 lb). Males tend to be slightly larger than females, but sex differences in body weight are overshadowed by enormous seasonal variation.

E. europaeus is unlike any other creature across most of its range. Where it co-exists with the northern white-breasted hedgehog (Erinaceus roumanicus), the two species are difficult to distinguish in the field, the latter having a white spot on its chest. According to the Guinness Book of World Records, E. europaeus is probably the largest species of hedgehog and is possibly the heaviest member of the order Erinaceomorpha, although the moonrat (Echinosorex gymnura), similar in average mass if not known to equal the hedgehog's maximum weight, can attain a considerably greater length.

In Europe hedgehogs carry a large number of hedgehog fleas (Archaeopsylla erinacei).

Colour variation

Leucistic or 'blonde' hedgehogs occasionally occur. Such specimens are believed to have a pair of rare recessive genes, giving rise to their black eyes and creamy-colored spines; however, they are not strictly speaking albino. They are extremely rare, except on North Ronaldsay and the Channel Island of Alderney where around 25% of the population is thought to be blonde. True albino forms of the hedgehog do also occur infrequently.

Behavior

This species is largely nocturnal. It has a hesitant gait, frequently stopping to smell the air. Unlike the smaller, warmer-climate species, the European hedgehog may hibernate in the winter. However, most wake at least once to move their nests. They are solitary in nature with mature males behaving aggressively towards each other. Occasionally a male and female may share a hibernating spot.

Diet

The European hedgehog is omnivorous, feeding mainly on invertebrates. Its diet includes slugs, earthworms, beetles, caterpillars and other insects. The preferred arthropods are the millipedes Glomeris marginata and Tachypodoiulus niger as well as the ground beetle Carabus nemoralis. Some fruits and mushrooms may supplement their diet.

Breeding

The breeding season commences after hibernation. Pregnancies peak between May and July, though they have been recorded as late as September. Gestation is 31 to 35 days. The female alone raises the litter which typically numbers between four and six, though can range from two to ten. Studies have indicated that litter size may increase in more northern climes. The young are born blind with a covering of small spines. By the time they are 36 hours old, the second, outer coat of spines begins to sprout. By 11 days they can roll into a ball. Weaning occurs at four to six weeks of age.

Longevity and mortality

European hedgehogs may live to ten years of age, although the average life expectancy is three years. Starvation is the most common cause of death, usually occurring during hibernation. If alarmed, the animal will roll into a ball to protect itself. Many potential predators are repelled by its spines, but predation does occur. Remains of hedgehogs have been found in the stomachs of European badgers (Meles meles), red foxes (Vulpes vulpes) and pine martens (Martes martes). A large portion of these may be from hedgehog carcasses, especially road-kill. However, hedgehogs tend to be absent from areas where badgers are numerous.

Eurasian eagle-owls (Bubo bubo) and golden eagles (Aquila chrysaetos) are the only regular avian predators of this species and may even prefer them as prey. The owl, after grabbing the hedgehog by its face, tends to skin the mammal's prickly back with its talons before consumption, resulting in several hedgehog backs being found around eagle-owl roosts and nests. In Spain, reduction of European rabbit (Oryctolagus cuniculus) numbers due to rabbit haemorrhagic disease has made the European hedgehog one of the top preferred prey species for eagle-owls. Elsewhere, eagle-owls often prefer these hedgehogs to any other prey species, as the hedgehog can comprise up to 23% by number and 30.7% by biomass of eagle-owl prey remains. On the Swedish island of Gotland the golden eagle may take larger numbers of hedgehogs than any other prey due to an otherwise low diversity of native land mammals, although the introduction of European rabbits has shifted the eagle's prey preferences there.

Distribution

The European hedgehog is endemic to Europe (including European Russia), with a global distribution extending from the British Isles and the Iberian Peninsula eastwards through much of western to central Europe, and from southern Fennoscandia and the northern Baltic to north-west Russia. Present also on Mediterranean islands (Corsica, Sardinia, Elba, Sicily), on most of the French Atlantic islands as well as on British Islands (autochthonous and introduced). It is an invasive exotic species in New Zealand and has probably been introduced to Ireland and many of the smaller islands where it occurs.

Colonists took hedgehogs from England and Scotland to New Zealand on sailing ships from the 1860s to the 1890s mainly for sentimental reasons. Few survived the 4-6 month voyage, but those that did had lost all their fleas. Animals found their first homes in the South Island, where their spread was helped by guards dropping them off at country railway stations. Hedgehogs were introduced to the North Island about 1906 and, from then on, their numbers increased at an exponential rate. By the 1920s they had become so numerous that game-bird hunters blamed them for reduced bag-sizes. Hedgehogs were declared noxious animals and a bounty of one shilling a snout paid by regional authorities for several years. By the 1950s, hedgehogs could be found over the whole country with the exception of the coldest wettest corner of the South Island and alpine areas of permanent snow. Nevertheless, hedgehogs have been seen climbing New Zealand glaciers. Hedgehogs do not reach the same weight in New Zealand as in colder parts of Europe. With its milder winters, New Zealand hedgehogs hibernate for only three months of the year so do not need to put on so much weight in autumn as their ancestors. In northern New Zealand, many hedgehogs do not hibernate at all. One of New Zealand's pioneer hedgehogs probably had faulty teeth for this feature is found in about 50% of today's animals. Most New Zealanders welcome hedgehogs in their gardens as they relish slugs and snails. Conservationists are less happy as hedgehogs compete for invertebrate food with native bush birds and prey on some rare insects, lizards and ground-nesting birds. As a result, extensive hedgehog-control programs are under way in some parts of the country, killing thousands of them. To judge by roadkill counts, North Island hedgehogs were at their highest numbers in the 1950s. Since then, roadkill counts have fallen dramatically from about 50/100 km to less than 1/100 km. refs Brockie, R.E. in Carolyn King (Ed) The Handbook of New Zealand Mammals. 1998. Oxford.

Habitat

The European hedgehog is found across a wide range of habitat types, encompassing both semi-natural vegetation types and those areas that have been heavily modified by man. The range includes woodland, grasslands such as meadows and pasture, arable land, orchards and vineyards as well as within the matrix of habitat types found in human settlements. It prefers lowlands and hills up to 400–600m, but is also locally present on mountains, exceptionally up to an altitude of 1500-2000m (e.g. Alps and Pyrenees). Outside cultivated land it prefers marginal zones of forests, particularly ecotonal grass and scrub vegetation.

Hedgehogs are most abundant within the gardens, parks and amenity land close to or within human settlements. They are generally scarce in areas of coniferous woodland, marshes and moorland, probably because of a lack of suitable sites and materials for the construction of winter nests (or hibernacula), which have specific requirements.

Protection

Generally, the hedgehog is widely distributed and can be found in good numbers where people are tolerant of their residence in gardens. To date, the IUCN classifies the species as Least Concern and currently the population as Stable. In some areas, they are common victims of road kills and may be hunted by dogs, such as in Sardinia. On 28 August 2007, the new Biodiversity Action Plan (BAP) included the European hedgehog on the list of species and habitats in Britain that need conservation and greater protection.

In Denmark and Poland, hedgehogs are protected by law. It is illegal to capture or hurt them, but the housing of underweight hedgehogs found outside during winter is accepted.

Hedgehogs are protected in all European countries which have signed the Berne Convention on the Conservation of European Wildlife and Natural Habitats.

A low coverage assembly of the genome of Erinaceus europaeus was released by the Broad Institute in June 2006 as part of the Mammalian Genome Project.

Population size

An estimate of 36.5 million by Burton was based on extrapolating up from a density of 2.5 animals/ha (one per acre), but this was based on limited data and is probably an overestimate. A more recent estimate of 1,550,000 in Great Britain (England 1,100,000, Scotland 310,000, Wales 140,000) is more reliable, but still has a high degree of uncertainty as it is based on very limited information about hedgehog density estimates for different habitat types. Given this figure, and more firmly established rates of decline, it is now thought likely that there are fewer than a million hedgehogs in Great Britain.

Population status

In 2007 the hedgehog was classified a Biodiversity Action Plan ‘priority’ species in Britain, largely in response to negative trends identified in national surveys such as Mammals on Roads survey, run by People's Trust for Endangered Species (PTES), that found an annual decline in counts of road casualties of around 7% from 2001 to 2004. Historic data from the National Gamebag Census suggest a steady decline between 1960 and 1980. Evidence from a questionnaire in 2005 and 2006 also supported an ongoing decline, with almost half of ~20,000 participants in PTES' Hogwatch survey reporting the impression that there were fewer hedgehogs than there were five years earlier.

A review of the available survey data for the population trend of the hedgehog in Britain was undertaken by the British Trust for Ornithology (BTO) in a report commissioned by PTES and the British Hedgehog Preservation Society (BHPS). This concluded that, at a conservative estimate, 25% of the British hedgehog population had been lost in a decade. The report also highlighted the importance of long-term monitoring to provide datasets with sufficient power to allow the changes to the population to be identified. Currently, the most important monitoring programmes involved in collecting information about the status of the British hedgehog population are PTES’ Mammals on Roads and Living with Mammals surveys, and the BTO Breeding Bird Survey and Garden BirdWatch survey. A recent review of these surveys now suggests that rural populations have declined by at least a half and urban populations by up to a third since 2000.

Pest status

This species has become a serious pest in areas where it has been introduced outside of its native range. One such location is the Western Isles of Scotland, where introduced hedgehogs eat the eggs of ground-nesting waders such as common snipe, dunlin, common redshank and northern lapwing. It is also considered a pest in New Zealand where it preys upon various native fauna.