Are hedgehogs declining in the UK and, if so, why?


It appears so; but it's been difficult to quantify. Over the years there have been various attempts to estimate the UK's hedgehog population, but all figures are guesstimates at best; we have no reliable method for surveying hedgehogs and without a decent handle on hedgehog numbers we struggle to say with any certainty whether numbers are increasing, decreasing or stable.

Circumstantial evidence from gardener questionnaires and the number of hedgehogs seen dead on the roadside implies that numbers are falling, perhaps dramatically, and recent figures in the media have quoted declines of up to 95%, from an estimated population of 36 million in the 1960s to fewer than a million today. This initial estimate is, however, widely considered to be a substantial overestimation. A recent comparative analysis of surveys conducted 25 years apart calculated that hedgehog abundance has declined by about 7% in England since the 1960s, but found the population to be more clustered now, implying a major population change. The 2015 State of Britain's Hedgehogs report suggests declines of up to one-third in our urban areas and 50% in the British countryside. The 2018 report notes a continued decline in rural hedgehog road casualties into 2017, while suggesting urban distribution may be changing, with fewer areas recording hedgehogs in 2017 vs. 2014, but more hedgehog seen in those areas where they were recorded. In a review of mammal trends based on survey data, published in British Wildlife during 2016, David Wembridge and Steve Langton note that Britain's hedgehog population has declined by 3.12% per year since 2003 in urban areas.

The proposed causes are many: changes to farming, and the move from pasture to arable in particular; application of pesticides, both on farms and gardens, with insecticides widely thought to both poison hedgehogs and kill their food; roads through collision with vehicles, roads restricting movement/recolonisation, and cattle grids); predators and the increase in the badger population particularly; and a variety of man-made hazards, including strimmers/mowers, discarded litter, bonfires, drowning in garden ponds, entanglement in netting, gardens that are “too tidy”, and even being fed inappropriate things, such as bread and milk, mealworms and peanuts. Fortunately, attitudes towards the environment are slowly changing and in recent years we've seen a move away from pesticides to use non-toxic methods of pest control and more appropriate supplemental feeding.

More sick and injured hedgehogs than ever before are also being taken to rescue centres, where they stand a better chance of being rehabilitated and released. Translocation of hedgehogs from island colonies where they are implicated in the decline of seabirds have also proved successful and offers hope for a possible “re-stocking” of some mainland areas. Furthermore, the evidence of a decline was considered sufficient for hedgehogs to be included (along with 17 other terrestrial mammals) on the British Government's UK Biodiversity Action Plan (part of the UK List of Priority Species and Habitats) in 2007.

The details

“Where have all our hedgehogs gone?” was one of several headlines to jump off the page of Tuesday 17th January 2006's The Guardian newspaper. Adam Nicholson's article painted a rather bleak picture of our hedgehog population and, at the end of his discussion, he summed up the problem very succinctly as:

The hedgehogs are dying because we don't know what we're doing to them. Without that knowledge, quite silently, an unobtrusive world is being mauled and, because it is largely invisible, nothing much is being said about it.”

The European hedgehog (Erinaceus europaeus) appears to be declining across much or Europe. - Credit: Kevin Robson

The idea that the British hedgehog population may be in decline is not a new one. In his Corgi Survival book The Hedgehog, published in 1969, Maurice Burton wrote how he had noticed the number of hedgehogs being killed on England's roads had fallen in the past few years:

My recollection is that from 1950 until now the [road] casualty rate per hundred miles in England has been much lower than for 1947. And my impression is that during the 1960s there has been a marked falling off in the numbers of hedgehogs has fallen throughout the country-side.

Similarly, most hedgehog books published since then have made some mention of a decline. A survey by the sustainability charity Environ, published in 2003, compared the number of hedgehog sightings to the same survey conducted in 1994 and found a 10% decline in the number of hedgehogs visiting the city gardens surveyed. Prior to these type of surveys, records from gamekeepers have suggested an 80% decline in hedgehogs caught between the 1960s and early 1990s, although these “gamebag” figures must be treated with caution because numbers can vary according to the changing opinion and effort of gamekeepers over the years. A survey of 2,600 people for the BBC Gardeners' World magazine in February 2017 found that only 49% of people saw a hedgehog in their garden in 2016, down from 52% in 2015; barely 10% saw a hedgehog regularly. As with the gamebag data, these surveys must be interpreted with caution. Without a trailcam most hedgehog visits to our garden would go unrecorded because they tend to happen in between about 11pm and 2am when few people are watching. The suggestion is, nonetheless, that hedgehogs are becoming less common.

So, we have at least some suspicions that hedgehogs are declining in the UK, but we lack the evidence needed by government and policy makers to justify imposing protection or diverting funds to redressing the problem. A significant part of the issue is that it is deceptively complicated and expensive to accurately estimate actual numbers of hedgehogs in Britain.

How many hedgehogs?

Tagging and tracking studies have provided valuable insight into the movements and habitat use of hedgehogs across Europe and this can be used to assess numbers. - Credit: Happy Hedgehog Rescue

Getting a handle on hedgehog numbers is not an easy task (see QA). Hedgehogs are reasonably small, nocturnal mammals that go about their business in an unobtrusive manner (they don't make many loud noises, or cause any major disturbance when feeding); they're also non-territorial and spend about one-third of the year in hibernation, away from prying eyes. Indeed, the only sign you may find that a hedgehog has visited your garden during the night is a dropping that's easily missed among grass or on loose soil.

There is an oft-cited estimation of 36.5 million hedgehogs in the late 1950s. This is an extrapolation, based on the amount of suitable hog habitat, of the hedgehog density of one per acre that Maurice Burton gave in The Hedgehog. Basically, this is a very rough extrapolation based on a couple of hours spent in Kew Gardens, and most biologists (including Burton) consider it is a substantial overestimate. The most recent attempt at an estimation was in 1995, which reached a figure of 1,555,000 hedgehogs in the UK, based on what we knew about hedgehog abundance in various habitat types: 1.1 million in England; 310 thousand in Scotland; and 145 thousand in Wales. This figure of 1.5 million is much more statistically robust than that based on Burton's estimate, but it is still just a best guess based on few data. Comparing this 1.5 million figure against 36.5 million in the 1950s suggests an almost catastrophic decline, but it very unlikely to paint an accurate picture. More recently The State of Britain's Hedgehogs report for 2015 suggested that, based on the surveys we shall review, the population probably stood at less than one million in 2010. No more recent estimates have been made, although there is a review of British mammals due to be published in 2017 that may provide some new data.

Going down?

So, if we don't have any empirical data to say hedgehogs are declining, where does the idea come from? The short answer is that it is largely a perceived decline—gardeners and naturalists have said that they've noticed fewer hedgehogs visiting their gardens, while motorists have reported fewer hedgehogs dead on the roadside and other wildlife surveys (such as gamebags, bird surveys and so forth) are generally receiving fewer sightings. The idea of a decline is not a new one and Maurice Burton wrote about how he was seeing fewer hedgehogs in the late 1960s. More recently, however, survey data have allowed us to have a stab at quantifying the decline.

The conclusion of Anouschka Hof in her Ph.D. thesis, completed at Royal Holloway in 2009, for example, was that the relative abundance of hedgehogs in the UK had fallen by about 16% in the previous 30 to 40 years. In 2011, the People's Trust for Endangered Species (PTES) and the British Hedgehog Preservation Society (BHPS) published the first The State of Britain's Hedgehogs report, in which they analysed data from five citizen science and volunteer surveys, most of which had been running since 2001. The report drew on data from the Living with Mammals (LwM), Mammals on the Roads (MoR), RSPB Garden BirdWatch, BTO Breeding Bird Survey and Waterways Breeding Bird Survey, to conclude that there had been a statistically-significant decline in the British hedgehog population between 1996 and 2010. The report author, David Wembridge, wrote:

“... at a conservative estimate a quarter of the population has been lost in the last ten years.

Updates to the State report, published in 2015 and 2018, suggested a continued decline in numbers. Overall, the Breeding Bird Survey recorded a roughly 14% decline in hedgehog records between 2011 and 2014, LwM reported about 3% fewer hedgehog sightings between 2003-2014 and the MoR survey recorded a decline in hedgehogs dead by the side of British roads of about 9% between 2001 and 2014, although counts were up in 2014 (similar to those in 2011), suggesting 2014 may have been a better year for hedgehogs.

A hedgehog killed on an urban street. One recent study suggested as many as 335,000 hedgehogs may be killed on Britain's road network every year. - Credit: Marc Baldwin

It may seem a little paradoxical to think that fewer hedgehogs dying on the roads is a bad thing; as a naturalist I could happily go the rest of my life without seeing another hedgehog lying lifeless on the road verge. In this case, however, it seems that fewer hedgehogs are dying on our roads because there are fewer hedgehogs around to be hit by cars. The decline in hedgehog road casualties, coupled with people simply saying that they don't see as many hedgehogs as they used to give sufficient cause for us to think that the hedgehog population is in decline.

Some recent data suggest that hedgehog populations might be changing in more than just size. In a paper to the European Journal of Wildlife in 2016, Anouschka Hof and Paul Bright compared hedgehog survey data collected between 2000 and 2015 to that recorded between 1960 and 1975. Using some nifty statistical models, they were able to account for the difference in survey effort between the two periods to compare indexes of relative hedgehog abundance in England. They found that, although hedgehogs were still widespread, there was a decline in occupied grid cells of between 5% and 7.4%, suggesting a moderate decline in the relative abundance of English hedgehogs. Furthermore, Hof and Bright observed a distinct clustering of records in the 2000-2015 dataset, even after accounting for effort—these were around some major cities, including Southampton/Portsmouth, London, Bristol, Birmingham and Leeds. In their paper, the biologists explain:

The 5.0-7.4% decline we detect here may well underestimate actual population change since the scale of our measurement was per force relatively coarse. The increase in clustering of records is however illustrative of a major population change.

The 2018 State report also suggested a change in distribution, with fewer areas reporting hedgehogs in 2017 than 2014, but an increase in sightings in areas where hedgehogs were reported—frequently in cities, towns and villages. Nonetheless, in a review of mammal trends based on survey data that includes road-kill, published in British Wildlife during 2016, David Wembridge and Steve Langton calculated that Britain's hedgehog population has declined by 3.12% per year since 2003 in urban areas.

The sum of all of the above can be emphasised with a quote from the UK Mammals report. The report used data from six surveys—the National Gamebag Census, Breeding Bird Survey, Waterways Breeding Bird Survey, Mammals on the Roads, Living with Mammals, and Garden Bird Watch—although two either surveyed largely unsuitable (riverside) habitat or had insufficient data for trend analysis. Based on the data from the remaining surveys, only one showed an increase in hedgehog sightings (the BBS) and the report concludes that:

The varied results from the surveys make overall interpretation quite difficult. This species can exhibit large between year fluctuations in population size that are not related to long-term trends, but it is likely that there has been a real long-term decline.

Footprint tunnels, baited with peanut butter or some other attractive food and with an ink pad at the entrance, are increasingly used to monitor small mammal presence. This tube, set in Canterbury in New Zealand, shows the inky footprints of a hedgehog. - Credit: Jon Sullivan

While surveying is far from the ideal option for monitoring mammal populations, for many species it is all we have. The important message here is to continue with surveys such as Mammals on Roads, Living with Mammals and HogWatch—as Nigel Reeve points out in Hedgehogs, a long time-series of comparable records is necessary in order to make solid judgements about our hedgehog population and how it may be changing.

The hows, whys & wherefores?

Knowing, or at least suspecting, that the hedgehog population is in decline is one thing but it is also important to try and get a handle on why this should be, so that it may at least be stopped or, ideally, reversed. Even before there was any real indication of a decline in numbers, scientists and animal welfare organisations alike were highlighting the plight of the hedgehog in our modern world. The malentities and misfortunes of hedgehogs are many and include: roads; pesticides; predators; habitat change; disease; strimmers and mowers; miscellaneous natural mortality (e.g., hibernation, old age, fights, climate change, etc.); and miscellaneous human-mediated mortality (e.g., litter and non-mechanised garden hazards).

The Long and Winding Road

Roads can take their toll on animals trying cross them. Anyone who has been a driver or passenger for a journey along pretty much any A or B road, dual carriageway or motorway can testify to it being neigh-on impossible to drive for more than a few minutes without seeing the carcass of a dead animal along the verge. Roads can also serve to fragment and isolate populations, inhibiting the gene flow between groups and preventing recolonization following local extinction. Additionally, roads can serve to concentrate pollutants in its vicinity. These issues are discussed at greater depth elsewhere (see QA).

Hedgehogs are—or were—familiar sights lying by the roadside. Ironically, it is the lack of hedgehogs to be found along the roadside that has been the driving force behind the idea that hedgehogs are in decline. Throughout the UK, some studies have suggested that hedgehogs die on the road at an average of one per kilometre (i.e., an average of 1.5 hogs per mile driven). The Mammals on Roads survey—a joint venture between the Mammals Trust and People's Trust for Endangered Species, which used driver surveys showing hedgehog casualties—recorded about a 70% decline in the number of dead hedgehogs between 2001 and 2015. There is variation in the casualty distribution and when you average the data out, you find that more hedgehogs seem to be killed per 100km of Scottish road than either English or Welsh road. In rural areas, the data suggest a decline in numbers of more than 7% per year. The consensus is that fewer are dying on roads because there are fewer around to be hit by cars.

Roads, particularly large fast ones such as motorways and dual carriageways, can be significant sources of mortality for wildlife and act as barriers to movement, resulting in habitat fragmentation. - Credit: Marc Baldwin

Outside of the direct mortality resulting from collisions with vehicles, hedgehogs also suffer mortality in cattle grids. Following public campaigns (largely championed by Major Adrian Coles, who went on to setup the British Hedgehog Preservation Society in 1982), there is now a trend for building escape ramps into cattle grids. Currently, in the UK, the design of cattle grids is regulated by the British Standard 4008 and BD37/88; ramps permitting the escape of small mammals, reptiles and amphibians are a recommended inclusion.

In his The New Hedgehog Book, Pat Morris made a rough calculation suggesting that about 15,000 hedgehogs were killed on Britain's road network each year. In a short paper to the journal Mammal Communications in 2016, however, David Wembridge and colleagues (including Morris) conducted a more systematic analysis of surveys conducted between 1952 and 2004, accounting for how long carcasses remain on the road and how likely you are to spot a hedgehog from a car.

The analysis estimated that between 167,000 and 335,000 hedgehogs died on our road network each year. This suggests that about 10% of Britain's hedgehogs die in collisions with traffic each year. Very few hedgehog experts think that roads are going to lead to the extinction of the UK's hedgehog population, but on a local scale it can have a large impact. Studies by Marcel Huijser and his colleagues in The Netherlands indicate that road traffic may reduce hedgehog population density by almost one-third in the 200m (~ 656 ft.) wide areas bordering roads. It is also a concern that we don't know how roads, in conjunction with the various other factors, add up to impact the hedgehog population.

Slugging it out

In recent years, there has been a massive drive towards a more ecologically friendly way of life, and one area where this has been particularly evident is in gardens. There is now a large culture of organic gardening, moving away from using pesticides to kill off species that eat your plants. Of particular concern for hedgehog welfare groups has been the unrestricted use of slug pellets on both a commercial and amateur basis. There is little doubt that slugs can do considerable damage to crops and some estimates put the number of slug pellets used annually in the UK to more than one million tonnes. Despite such a liberal application of mollusciside, it was not until the mid-1970s that any work was done to establish what impact these might have on hedgehogs that come into contact with them (see QA for more detailed coverage).

A variety of slug-killing chemicals are available in garden centres. It is suspected that the routine application of these treatments not only removes a potential prey source for hedgehogs, but may also result in direct or indirect poisoning. - Credit: Marc Baldwin

Death as a result of consumption of slug pellets is typically considered unlikely. Food preference studies suggest that, although hedgehogs will eat the pellets in the laboratory, they don't actively choose them over regular prey. According to Morris, Swiss biologist Schlatter calculated that it would take about 250 mg of metaldehyde to kill a 500g (1 lb.) hedgehog, suggesting the consumption of about 5,000 poisoned slugs, or 800 pellets. Metaldehyde doesn't appear to accumulate in tissues or the environment, so it seems unlikely that a hedgehog could easily reach the lethal 250mg level. Absence of evidence is not evidence of absence, however, and hedgehogs have been found suffering from metaldehyde poisoning. Some authors have found sufficient levels to conclude that this was the cause of death and remain convinced that hedgehogs can and do eat enough pellets to result in serious poisoning or death. In The Complete Hedgehog, Les Stocker explains that, in his experience, the “classic symptoms of metaldehyde poisoning” in hedgehogs are extreme excitement and tremors, with some muscle stiffening and even partial paralysis.

Whether or not hedgehogs are particularly likely to be killed by slug pellets, it has been suggested that they may suffer sublethal effects (reproductive failure, behavioural changes, etc.) that could impair their survival or reproduction. They may also suffer from the same decline in invertebrate prey (through the application of various pesticides) that has been linked to a drop in farmland bird species.

One man went to mow…

In recent years, the increasing popularity of electric lawn mowers and strimmers have become a problem for hedgehogs. We have already seen that, when confronted with danger, hedgehogs seldom flee; rather, they curl up and rely on their spines to afford them protection. Unfortunately, spines are just as ineffective against lawn mowers and garden strimmers as they are against cars. What's worse is that hedgehogs like to lie up in the exact lanky, overgrown vegetation that many gardeners want to mow or strim. In an article to the May 2000 issue of BBC Wildlife Magazine, Pat Morris wrote:

A newer threat comes from the proliferation of mowing machines, which slice not just grass, but also the legs, nose and skin of sleeping hedgehogs. While other animals would flee to safety at the sound of an oncoming strimmer, hedgehogs lie there motionless, relying naïvely on their spines for protection.”

Strimmers pose a significant risk to hedgehogs, which choose areas of long grass and leaves to nest. Strimmer-related injuries, included amputated spines, noses and legs, are increasingly seen by hedgehog rescuers. - Credit: Marc Baldwin

There is no central database of hedgehog admissions to wildlife rescue centres, so we have no “official” figures for how many are injured by strimmers. That said, on their website the Epping Forest Hedgehog Rescue team report that in 2007 they had 50 hogs brought in with injuries caused by strimmers and it appears this is about average for the rescue. Unfortunately, none of the hedgehogs survived, despite the veterinary care administered. Elsewhere, Jayne Morgan, who runs The Happy Hedgehog Rescue in Yatley, tells me she received at least 20 hogs with strimmer injuries during 2016, an increase over the 15 they had the previous year.

In 2014, Hedgehog Bottom rescue in Thatcham, Berkshire took in 722 hedgehogs, 173 (24%) of which suffered from “gardening injuries”. Hedgehog Bottom founder Gill Lucraft tells me that almost all of these were strimmer-related injuries, with a few mower-related and seven animals impaled on garden forks. This was a pretty typical year for the rescue, apparently. The Jersey Hedgehog Preservation Group, meanwhile, admitted 580 hogs during 2016, about 10 (1.7%) of which were suffering from strimmer-related injuries—this follows a significant publicity campaign on the island aimed at reducing such incidents. In some cases, skin grafts are possible, but in many instances the hedgehogs do not survive. Over the country as a whole, the number of hedgehogs that could be saved if people took a moment to check before strimming, lighting their bonfire or turning their compost heaps must be sizeable.

There is a thought-provoking (if a little macabre) poem by the fantastic late poet, novelist and even jazz critic Philip Larkin on the subject of hedgehogs and lawn mowers, spawned from a fateful day in June of 1979, when he was pushing a Victa lawnmower—which, rumour has it, he never used again—around his garden in Hull. In his poem entitled “The Mower”, Larkin wrote:

The mower stalled, twice; kneeling, I found
A hedgehog jammed up against the blades,
Killed. It had been in the long grass.
I had seen it before, and even fed it, once.
Now I had mauled its unobtrusive world

It cannot be over-emphasised how important it is to check the area to be cut before starting. It sounds rather melodramatic, but a few minutes of your time really can mean the difference between life and death for a snoozing hedgehog.

Digging the dirt

The Honourable Lady Nicolson (better known as the English poet, novelist and gardener Vita Sackville-West) is quoted as saying: “The man who has planted a garden feels that he has done something for the good of the world.” Gardening is certainly an increasingly popular pastime and the 2014 report by Verdict Research estimated the UK gardening sector to be worth almost £13 billion per year; a figure increasing year on year.

Following the First World War (1914-1918), Britain saw a change to its farming practices, with a shift away from more traditional grazing pastures towards arable (crop) farming; horses were replaced by machinery and hedgerows removed to make the fields large enough to accommodate the vehicles and maximize available space for crops. In The New Hedgehog Book, Pat Morris notes how, over the past 50 years or so, we have seen the replacement of small, closely-grazed fields, with plenty of invertebrate-rich dung and hedgerows, with large, intensively-farmed arable (mainly cereals) fields treated with various chemicals manufactured to kill the “pests” that hedgehogs feed on.

The value of mature hedgerows to wildlife, particularly hedgehogs, cannot be underestimated - providing food, nesting sites and material and shelter from the elements and predators. - Credit: Tim Sheerman-Chase

The importance of hedgerows as a habitat for hedgehogs cannot be overemphasised. During their tracking study of hedgehogs in a 202 hectare (2 sq-km, or three-quarters sq-mi) area near Elbug in The Netherlands, Marcel Huijser and his colleagues found that, although hedgerows only comprised about 10% of the study site, hedgehogs spent one-third of their time in them and along the edge of woods; altogether, they spent 60% of their time either in or within 5m (16.5 ft.) of hedgerows or forest edges. Huijser and his team also observed that 82% of 271 day nesting sites they located were found among bramble bushes, dense shrubs or grasses and herbs situated within hedgerows (60%) or woods (22%). The biologists were only able to locate 15 hibernacula but, of these, almost 90% were found either in hedgerows (46.7%) or in wooded areas (40%); similarly, all eight breeding nests were located in one of the two habitats (six in hedgerows, two in woods). While tracking hedgehogs around Nottinghamshire, Richard Yarnell and his team found that just over half the nests they found were in bramble and hedgerow and, while studying hogs for her Ph.D. at Oxford University, Carly Pettett found that hogs preferred to nest in shorter and wider hedges and that hedgerows were warmer than surrounding fields.

With hedgehogs apparently so dependent upon hedgerows to provide safe resting, hibernating and breeding nest spots, it is not difficult to see how the loss of these landscape features is likely to be problematic. According to DEFRA, between 1984 and 1991 England has lost 21% of its hedges, while Scotland and Wales have lost 27% and 25%, respectively (overall, within the UK some sources suggest we now have half the length of hedges now than in 1950); losses are a result of a combination of direct removal and neglect. In many arable fields, ancient hedgerows (those in existence since the passing of the Enclosure Acts, mainly between 1720 and 1840 in Britain and from the mid seventeenth century in Ireland) have all too often been replaced by tree stumps or wire strung between posts.

We know from tracking studies that hedgehogs make little use of arable fields, preferring pasture land that provides a mixture of short grassland and scrub/hedge patches for nesting. While there has been a recent drive by the government and farmers to try and restore some of our countryside and farm it in a more sustainable manner, it is not difficult to see why many gardens, with their short lawns and mixture of trees, bushes and grasses, provide a refuge for hedgehogs. Not all gardens are equal, however, and not all provide the habitat needed by hedgehogs. People who take pride in their gardens being neat, tidy and pest free are unlikely to receive more than transient visits from hedgehogs.

Gardening for the future

Fortunately, one sector of gardening that has seen a considerable expansion during the last 20 years is “wildlife gardening”. A significant stimulant for this pastime has been the book How to Make a Wildlife Garden, by Urban Wildlife Trust president Chris Baines. Part of the appeal of wildlife gardening is not just that it attracts various species to your garden, but also that you don't need a massive garden to make it happen—in chapter three of his second edition (2000), Baines writes:

Don’t imagine you need a five-acre country estate before you can begin to plan for wildlife. Even a window box can provide a welcome resting place for passing butterflies if you plant the right flowers...”

Large gardens, particularly those with a mix of short grass on which to hunt beetles and worms and mature bushes/shrubs for cover and nesting material offer ideal habitat to hedgehogs. - Credit: Marc Baldwin

The crucial aspect of creating a wildlife garden is variety; a variety of different habitat types (from trees and bushes, to flower beds and ponds). As a general rule of thumb, the greater the diversity of habitats you can provide, the more wildlife you garden will attract. The reason for this is simple: more habitats provide more sources of food and a greater number of different shelter features. In the case of hedgehogs, they like the short-cut grass of lawns (which provides excellent worm and beetle hunting) but also the seclusion of dense bushes which provide resting sites and nesting material for hibernaculums. Ponds provide a welcome source of freshwater for most species and log piles are a hotbed of insect activity.

Unfortunately, gardens or any sort are increasingly under threat. Under the UK government's Planning Policy Guideline 3 (PPG3), gardens are considered “brownfield sites”. In their broadest context, brownfield sites are any areas of land that have previously been developed. Most typically, brownfield developments are flats that go up on the sites of previous houses or factory sites. With brownfield land including that attached to a development, however, householders are free to sell their gardens to developers, who invariably build more houses on it. Moreover, there has been a trend for developers to buy bungalows (which often have large gardens attached), knock them down and build flats on the former building and its garden. The rush to develop brownfield land is perhaps not surprising, given the UK government's target of building three million new homes by 2020.

Garden hazards

Where gardens remain, it is worth bearing in mind that they can also pose a considerable number of hazards for hedgehogs. While hedgehogs can swim, they can easily drown if they fall into a pond with sides too steep to climb out. If digging a wildlife pond, at least one side should have a shallow slope to allow easy access to, and escape from, the water—alternatively, a short plank of wood (wrapped in chicken wire for extra grip) can be situated at one end to act as an escape ramp. As with escape ramps from cattle grids, the gradient shouldn't be too steep; not more than 30-deg from horizontal.

Hedgehogs frequently become entangled in netting, particularly low-hung netting used to protect plants from birds. - Credit: Hedgehog Bottom Rescue

Netting can also be a big problem for hedgehogs. In The Complete Hedgehog, Les Stocker writes: “Hedgehogs make a habit of getting trapped in the plastic bean netting, twisting and turning until they nearly sever a leg or seriously damage their throats.” It is recommended that garden netting is started at least 30cm (1 ft.) above the ground. Pea and bean netting aren't the only culprits; as a child, I recall watching with interest as a member of staff from a local leisure centre took the utmost care untangling a hedgehog from a football goal net.

The provision of the wrong types of food can also pose a problem. We have seen elsewhere on this site that bread and milk, while commonly offered to hedgehogs, doesn't represent a good source of nourishment and can lead to diarrhoea. Similarly, people involved in rehabilitating hedgehogs can cause problems if they provide only pet food. In an article published in the Veterinary Record during 1996, Pat Morris and biologists from the Institute of Zoology's Veterinary Science Group report on the fate of 12 hedgehogs kept for one winter at an animal hospital in Somerset before being released back into the wild. During the pre-release health checks the biologists found that all of the animals had inflamed gums, a response, the authors believe, to the diet of soft food (pet food, insect mix and day-old chicks) offered in captivity, which sticks to the gums and can lead to microbial infection.

The authors suggest that, in the wild, the hard exoskeletons of insect prey probably serve to scrape plaque and tartar off the teeth, helping to maintain dental health. The recent trend for householders to feed hedgehogs copious quantities of mealworms and peanuts may lead to future issues. These are very high in phosphorous, relative to calcium, and this retards calcium absorption in the stomach—the result can be osteodystrophy and bone metabolic disease. Some rescues have recently started seeing hedgehogs with bone deformities that they suggest might be a result of bone-thinning from too many mealworms and peanuts.

We have already seen that hedgehogs have something of a penchant for falling into things, so it is not difficult to see how uncovered garden drains can represent a threat. Similarly, the application of pesticides (by you or your neighbours) can have an impact on the wildlife you see in your garden. There are also more seasonal hazards, such as bonfires. Every autumn there is a plea from hedgehog carers for people to check in that pile of old wood and garden refuse for hedgehogs before setting it on fire. Again, there aren't any national stats so we don't know how many hogs are killed in bonfires each year. In the literature, the only specific reference is a 1988 paper to the Journal of Zoology in which Chris Dickman reports that almost 2% of the 109 corpses he studied had died from burns. Talking to some of the hedgehog carers I know, they see very few burn victims (maybe only one or two per year), but they suspect this is probably because most either go unnoticed or get thrown away.

Les Stocker sums the situation up well when he wrote: “Remember, if there is a hazard in the garden, a hedgehog is bound to find it.

Don’t drop it. Bin it.

Outside of the garden, the problem of littering can be a major problem to wildlife and, because of their inquisitive nature, hedgehogs seem particularly susceptible. In The Complete Hedgehog, Les Stocker writes of cases where hedgehogs have crawled through various plastic hoops, elastic bands and key rings, which have become lodged and cut into the animal as it grew. Hedgehogs are also renowned for getting their heads stuck in yoghurt pots and tin cans. Perhaps the most famous of these are the McFlurry® pots, which contain a variety of ice cream fillings and are sold by the fast-food chain McDonald's. The pots consist of two parts, the cup itself (this is cardboard, standing about 8.5 cm tall and is about 9cm/3.5 in. at the neck) that holds the ice cream and a plastic lid that clips on to the cup—it is the lid that has caused the problem.

A McDonald's McFlurry pot. - Credit: Marc Baldwin

The problem with the original design of the McFlurry® pot was that it had a hole just large enough for a hedgehog to get its head in; unfortunately, the lid had a deep lip that catches on the spines and prevents the hog from pulling its head back out. In September 2006, following five years of pressure from the British Hedgehog Preservation Society and the public, McDonald's released the new look pot design, with a smaller hole (now 3.5 cm/~1.5 in. wide) that's designed to prevent hedgehogs getting their heads into. The lid also now contains the warning “Bin it - Litter can harm wildlife” in raised letters. While I don't doubt this will help adult hedgehogs (which must be a step forward) it strikes me that juvenile animals will continue to face the problem. In my opinion, it is disheartening that McDonald's even needed to redesign their packaging, when the problem can be so easily overcome with a little thought on the part of the people disposing of their litter.

Nature, red in tooth and claw

To this point, I have talked largely of the anthropogenic (man-made) threats to hedgehogs: roads, pesticides, garden hazards, litter, etc. There are, however, numerous “natural” sources of injury and mortality faced by hedgehogs. After all, everything that lives will eventually die and hedgehogs are certainly no exception. Indeed, assuming a hedgehog lives to see the outside of its nursery nest (some 20% won't), the single biggest threat it faces is hibernation. Hibernation is a major physiological readjustment and an inherently dangerous undertaking. It is estimated that as many as 70% of hedgehogs don't survive their first year and half of those will die during their first winter. During hibernation, hedgehogs are vulnerable to predators, flooding and quite literally running out of fuel (if sufficient fat reserves cannot be deposited during the summer and autumn months).

Next to hibernation predators probably represent the second biggest threat to a hedgehog's continued survival. Hedgehogs have relatively few predators, but seem to feature fairly high on the badger's menu; foxes are also widely reported to take them, but probably to a lesser extent than badgers (see QA). Badgers are widely implicated in the decline of hedgehogs across the UK; data from tracking studies suggest that the location of badger setts can present a strong barrier to hedgehog movement, and that hogs respond to badger odour by making a bee-line away from areas of badger habitation. Some authors have suggested that part of the reason hedgehogs do well in the urban sprawl of our settlements is that these areas tend to provide respite from badger predation. In addition, The State of Britain's Hedgehogs 2015 report points out that badgers also compete for food with hedgehogs, noting that “one badger eats enough to support five hedgehogs”. Hedgehogs may also be killed by overzealous domestic dogs, although it is unknown how often this happens.

Badgers aren't just predators of hedgehogs; they're also their competitors. Badgers are adept wormers and one can eat several hundred worms in a single night, enough to support several hedgehogs. - Credit: Alan Baldry.

Hedgehogs may drown in ponds, lakes and even in the sea. They may also fall foul of various parasites (especially lungworm) and diseases or may contract infections in cuts, bites and scratches obtained while fighting with conspecifics (i.e., other hedgehogs) or predators. Alternatively, in presumably rare cases (for wild animals), they may die from the organ failure associated with old age.

Feeling hot, hot, hot!

One final aspect to consider is climate change. While scientists continue to argue as to the causes, there is no longer any doubt that our climate is changing: it's getting warmer. A warming climate per se may not be a major threat to hedgehogs and they do well in warmer climes such as the milder winters of New Zealand's north island. Provided their food supply doesn't disappear, we will probably just see a reduction in the period spent in hibernation, or an abolition of hibernation altogether. The big problem comes in the form of unpredictable cold snaps.

Coming out of hibernation uses up a considerable amount of energy. So, when we experience several weeks of mild, wet weather during winter hedgehogs wake up more frequently than normal and go looking for food, which may or may not be there to find. Provided the weather holds and the food remains, this wouldn't necessarily pose a threat to survival. These mild weeks are, however, often punctuated by shorter spells of very cold weather—this caused the hogs' natural food to disappear and can lead to hedgehog starvation. Furthermore, the cold may trigger the hog to re-enter hibernation and, having used so much energy waking up, it may not have sufficient reserves to see it through the rest of winter—particularly if there are several mild spells. Ideally, we need warm summers and fairly consistently cold winters in order for hedgehogs to hibernate “properly”; less well defined seasons are almost certainly bad news.

Climate change and the unpredictable/changeable weather that it brings could be the final straw for Britain's hedgehogs. - Credit: Marc Baldwin

I have said that a generally warmer climate may not be a big deal for hedgehogs, but I must stress that the overriding provision here is that the food supply isn't detrimentally influenced. Unfortunately, there is good reason to think that changes to the climate will lead to changes in the breeding cycles of insects. If this change is drastic, even hedgehogs—which feed on a large variety of different things—may not have time to adapt and may therefore face extinction.

The future

I hope that by this stage, I have convinced you of the need to monitor animal populations—without this it is feasible to think that they could fade into extinction. After all, we can't help conserve something if we don't know what's causing it to decline in the first place. Fortunately, while there is still considerable cause for concern, there are some positive aspects of the hedgehog's case. We have seen that there is already a substantial trend towards wildlife-friendly gardens; people are also encouraged to put out food for their local hogs and even to splash out of custom-built hedgehog houses that provide a safe spot to pass the winter months—these houses may not protect against the effects of climate change, but they do provide refuge from predators, strimmers and (provided they're placed correctly) flooding.

The UK Post-2010 Biodiversity Framework, published in July 2012 by the JNCC and Defra, sets out the government's conservation strategy until 2020. - Credit: Joint Nature Conservation Committee

Conservation organisations have also gone a long way in recent years to publicise the threats that hedgehogs are facing; this is especially true around bonfire night and when it comes to strimmer and mowers. Public support in the form of donations (time and money) allows charities to rescue, rehabilitate and release sick and injured hedgehogs, which probably helps boost the population. The fortunes of translocated hedgehogs have recently been studied and it seems that it is entirely feasible to move hedgehogs from islands such as Uist in the Outer Hebrides, where they are implicated in the decline of local seabird populations, to the UK mainland in order to bolster numbers—the question of how well hedgehogs survive when released from captivity is discussed in a separate QA.

Protection, championed by conservation societies, is one thing but in many cases legislation and action is required by governments. In August 2007, the hedgehog was included along with 1,148 other species of animals and plants on the British government's Biodiversity Action Plan (BAP). The idea of the BAP is to describe the UK's biological resources and set out a detailed plan explaining how these resources are to be protected. Since the BAP was drawn up, there is little doubt that it has played an important part in focusing attention on species in trouble, and the protective measures implemented seem to have led to some dramatic increases in several bird species. The revised list is, however, now almost twice as long as the original list, which was drawn up in response to the 1992 Convention on Biological Diversity.

Research is currently under way by a number of different bodies and data collected by scientists, coupled with that provided by the general public (driver or garden surveys) will, we hope, provide a clearer picture of what is happening to our hedgehogs and, perhaps more importantly, why. It is to be hoped that, through a combination of research, education and government policy the hedgehog will be around for many more generations to enjoy.