Hedgehogs

Chosen as Britain's favourite mammal, the Western European hedgehog (Erinaceus europaeus) is cute and charismatic, but these prickly animals are in worrying decline.

Hedgehogs are unmistakeable nocturnal mammals; they 20-25cm long, weigh up to 1.2kg, and are covered in around 6000 yellow tipped spines. Hedgehog spines are made from keratin and used for defence - if threatened, a hedgehog will curl up into a prickly ball by contracting a muscle which runs around it's body. The primary predators of hedgehogs are badgers, though hoglets are also at risk of predation from foxes, and in some places tawny owls, golden eagles, pine martens, weasels, stoats and rats. 

Hedgehogs themselves are also predators, and emerge at night to eat a variety of invertebrate prey. The species makeup of hedgehog's a diet will vary throughout the year, but incudes earthworms, slugs, and beetles, and sometimes carrion and the eggs of ground nesting birds. As they hunt in darkness, hedgehogs don't need good eyesight and navigate mostly using smell and hearing. Hedgehogs are solitary and have home ranges where they will hunt, but are not territorial. The size of their home range varies between the sexes but is typically between 10 and 20 hectares. On average, individuals travel 2km a night to feed, and when looking for a mate in the breeding season, males may travel up to 3km. Hedgehogs occupy a range of habitats, including woodland, grassland, parks and gardens.


A hedgehog on a suburban street

The annual phenology of hedgehogs is interesting - they are one of just 3 British mammals that hibernate. In October/November hedgehogs make a nest of fallen leaves and enter a state of torpor, which slows their bodily functions and saves energy. This lasts until March/April, but they often move to another nest site at least once during this time. Being disturbed from hibernation can have severe detrimental impacts on hedgehogs, as it uses a lot of energy for them to become active again. From spring through summer hedgehogs mate, initiated by the male displaying by noisily puffing and circling the female. Challenges from other males can lead to chases and headbutting. Litters of 4-5 hoglets are born in summer, though usually only 2 or 3 are successfully weaned. After around a month hoglets venture out to forage with their mother, then alone 10 days later. Hedgehogs reach sexual maturity at about 12 months old, and typically live 2 to 3 years, but can live up to 7. 

Once a common sight across the UK, hedgehog populations have declined sharply in recent years. A method to reliably estimate numbers is yet to be established, but multiple surveys by NGOs have suggested staggering declines; since 2000, the number of hedgehogs in urban areas is thought to have decreased by a third, and halved in rural areas. This is due to a variety of threats, one being habitat loss and degradation. Destruction of habitat deprives hedgehogs of food and shelter, leaving them vulnerable to starvation and predation by badgers. Development of land and erection of impermeable fencing breaks up hedgehog habitat, fragmenting it into areas too small to be functional. Pesticide use in agriculture and in gardens also harms hedgehogs by reducing their food supply. Due to the timing of hibernation, hedgehogs are also at risk of being killed in bonfires, as they can attempt to nest in the assembled fires, which are then set alight.
 
Possibly the primary threat to hedgehogs is roads - an estimated 167,000–335,000 hedgehogs are killed on Britain's roads each year. The mortality rate peaks in July when hoglets leave to forage alone. Certain areas have higher roadkill rates, with the most deaths recorded on roads adjacent to grassland and in urban outskirts. Efforts to reduce hedgehog roadkill involve research to discover high risk areas, often through charities such as The Mammal Society and PTES encouraging the public to submit their records of hedgehogs, dead and alive. Potential mitigation methods in these areas include reducing speed limits in hotspots, and installing bridges and tunnels, though these are only effective when crossing points are at restricted locations. Improving habitats parallel to roads can also discourage hedgehogs from crossing. 

Other conservation methods to reduce hedgehog decline include helping landowners manage their land for hedgehogs. An example of this is the guide for farmers published by Hedgehog Street, which recommends reducing ploughing, reducing field sizes and increasing hedgerows and scrub areas. The British Hedgehog Preservation Society also runs the 'Hedgehog Friendly Campus' campaign, encouraging universities to improve their land for hedgehogs. UEA has achieved silver accreditation from this scheme. 

A hedgehog highway hole in a fence on the UEA campus

Individuals can also help conserve hedgehogs by having hedgehog houses in their gardens, leaving log piles, overgrown areas and compost heaps and providing food and water. People can help ensure no hedgehogs die horrible death in bonfires by building them just before use, or thoroughly checking and flushing out any nestled in hogs. 


A hedgehog snacking on some food left out in a garden.

If a collective effort is made to help these spiky mammals they could return to healthy numbers once again. 
 

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