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 malenities and misfortunes of hedgehogs are many and include: Roads; Pesticides; Predators; Habitat Change; Disease; Strimmers & 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.
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 ½ 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 a 20% decline in the number of dead hedgehogs between 2001 and 2005. Indeed, the surveys found that the number of hedgehogs being killed on our roads was closer to one or two per 100km (67 ½ mi.) driven in the south of England in 2004 – in the east of England, road casualties have halved between 2002 and 2004. In rural areas, the data suggest a decline in numbers of more than 7% per year. Quite plainly, hedgehogs haven’t learnt their Green Cross Code (which is, perhaps ironically, advertised using cartoon hedgehogs); rather fewer are dying on roads because there are fewer around to be hit by cars.
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.
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 Dr 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
Death as a result of consumption of slug pellets is typically considered unlikely – from food preference studies it seems that, although hedgehogs will eat the pellets in the laboratory, but there is no evidence to suggest that they are actively chosen over regular prey. According to Dr Morris, Swiss biologist Prof. Schlatter calculated that it would take about 250 mg of metaldehyde to kill a 500g (1 lb.) hedgehog. Based on this, it has been suggested that a hedgehog would need to eat somewhere in the region of 5,000 slugs, or some 800 pellets, before it hit the 250mg dose. Given that metaldehyde doesn’t appear to accumulate within biological tissues or the environment, it is generally considered unlikely that a hedgehog could reach the 250mg level. Nonetheless, hedgehogs have been found suffering from metaldehyde poisoning and some authors have found sufficient levels to conclude that this was the cause of death – similarly, some authors remain convinced that hedgehogs can and do eat sufficient pellets to result in serious poisoning or death. In The Complete Hedgehog, Mr. 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.
The problems associated with getting an idea of hedgehog numbers also pose problems for getting a handle on pesticide poisoning. The point here is that simply because hedgehogs seldom show up with signs of molluscicide -- or more generally, pesticide -- poisoning does not mean that they are not at risk from it. Moreover, there is very little information regarding how other (i.e. non-molluscidal) pesticides affect hedgehogs. Pesticides such as dieldrin and chlordane (the latter of which was used to kill earthworms!) have been banned by most governments, but animals still turn up having died from dieldrin poisoning, which points to the persistence of this toxin in the environment.
Whether or not hedgehogs are particularly likely to be killed by slug pellets, it has been suggested that they may 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; still, evidence for this is currently lacking.
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 motor vehicles. 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 naively on their spines for protection.”
If any (more graphic) proof were needed to testify that hedgehogs come off worse from encounters with strimmers, it can be found on Derek and Sandra Knight’s (together they are Epping Forest Hedgehog Rescue - EFHR) website (Warning: Some photos may cause distress). There don’t appear to be any official statistics on how many hedgehogs are killed or injured each year by strimmers and mowers, but last year (2007), EFHR took in more than 50 animals suffering from strimmer injuries – on their website Derek and Sandra write: “Believe it or not 2007 was NO WORSE than any previous year.” The couple go on to say that none of those unfortunate hedgehogs survived, despite the veterinary care administered.
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 (UK). 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
Unmendably.
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.
"Feeling lucky, punk?"
[You must be registered and logged in to see this image.]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 latest (June 2006) UK Market Synopsys of Gardening and Garden Services estimates the UK gardening sector to be worth some £5 billion per year; moreover, this figure is increasing at a rate of some 20% per annum.
Following the First World War (1914 to 1918), Britain saw a change to its farming practices, with a shift away from more traditional grazing pastures towards arable farming; horses were replaced by machinery (with 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 dung (very rich in insects and a veritable buffet for hedgehogs) and hedgerows, with large, intensively-farmed arable (mainly cereal crop) fields treated with various chemicals manufactured to kill the ‘pests’ that hedgehogs feed on.
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 3/4 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 33% of their time in them and along the edge of woods; altogether, they spent 60% of their time either in or within 5m (16 ½ ft) of hedgerows or forest edges. Dr 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 (6 in hedgerows, 2 in woods).
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. However, not all gardens are equal, 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.
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), Mr. 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…”
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. However, with brownfield land including that attached to a development, it has meant that 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 every available scrap of brownfield land is perhaps not surprising, given the UK government’s target of building three million new homes by 2020. Fortunately, despite the increase in house building, not everyone is willing to sell off their back garden; to quote the American naturalist Henry David Thoreau: “In wildness is the preservation of the world.”
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 (like many other small animals) 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 30o from horizontal.
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 (1ft) above the ground. Pea and bean netting aren’t the only culprits; I recall watching with interest a member of staff from a local leisure centre take the utmost care to untangle a hedgehog from a football goal net when I was a child.
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 (UK) 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.
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 don’t seem to be any statistics for the number of hedgehogs killed or injured in bonfires (presumably many go unnoticed) but in a 1988 paper to the Journal of Zoology, Dr Chris Dickman reports that almost 2% of the 109 corpses he studied had died from burns. Mr Stocker sums the situation up well when he writes: “Remember, if there is a hazard in the garden, a hedgehog is bound to find 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, Mr Stocker writes of cases where hedgehogs have crawled through various plastic hoops 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 and other dessert pots. 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 ½ cm tall and is about 9cm/~3 ½ in. at the neck) that holds the product and a plastic lid that clips on to the cup – it is the lid that has caused the problem.
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 ½ cm/~1 ½ in. wide) that’s designed to prevent the hedgehog getting its head into the pot in the first instance. 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 still face the same 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. However, there are 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, the goal of which is to reduce the animal’s metabolism (in the case of mammals, by turning down their internal ‘thermostat’) thereby conserving precious energy stores during periods when food is in short supply – it is 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 of the hibernaculum 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. The impact that foxes and badgers seem to have on hedgehog numbers is discussed in a separate Q/A. Suffice to say that 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. Hedgehogs may also be killed by over zealous domestic dogs, although this can hardly be considered predation and, more often than not, it is the dog rather than the hedgehog that comes off worse from the encounter.
Hedgehogs may drown in ponds, lakes and even in the sea. They may also fall foul of various parasites (especially lungworm) and diseases (see Q/A) 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 when talking of threats to hedgehogs is that of 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 (it does seem to be causing serious problems for some species, while others are thriving); hedgehogs do well in warmer climes (e.g. in the milder winters of New Zealand’s north island) and provided that 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.
Hedgehogs begin feeding ravenously during the late summer and autumn months in order to lay down sufficient energy reserves (i.e. fat) to last them through the winter. They may enter hibernation at any time between November and January and will generally remain inactive (excluding periodic arousals, shuffling and perhaps moving to a new hibernaculum) until April. Coming out of hibernation uses up a considerable amount of energy. So, when we experience several weeks of mild, wet weather during winter we see the hedgehog’s food (slugs, insects etc.) out and about – the warmer temperatures can lead the hedgehog to arouse from hibernation, under the false impression that it’s spring. Provided the weather holds and the food remains, this wouldn’t necessarily pose a threat to survival. However, these mild weeks are often punctuated by shorter spells of very cold weather – this leads to a rapid decline in the insect and mollusc population (i.e. the hedgehog’s food) and can lead to starvation of the hedgehogs. The hedgehog will have used most of its energy reserves arousing from hibernation, so if it re-enters hibernation it will almost certainly die of starvation. Ideally, we need warm summers and cold winters in order for hedgehogs to hibernate ‘properly’; less well defined seasons are almost certainly bad news.
I have said that a generally warmer climate may not be a big deal for hedgehogs; 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.
Warming weather punctuated by sudden cold snaps (especially with heavy frosts or snow) are bad news for hibernating animals
Redressing the balance
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 (by organisations such as The Mammals Trust, British Hedgehog Preservation Society, Mammal Society etc.) to put out food for their local hogs and even to splash out of custom-built hedgehog houses that provide the creatures with 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.
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. The example of Epping Forest Hedgehog Rescue illustrates how local organisations can play a role that is just as important as the nationwide charities. Public support (in terms of donations – both of time and money) allows charities to rescue, rehabilitate and release sick and injured hedgehogs, which invariably provides a lifeline for these animals. The fortunes of translocated hedgehogs has recently been studied by several groups of biologists and it seems that it is entirely feasible to move hedgehogs from islands such as Uist in the Outer Hebrides (where they are heavily 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 Q/A.
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 12 years ago, 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 lead to some dramatic increases in several bird species. However, the revised list is 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, including the University of London and Bristol University (who are due to undertake a new PhD project looking into the factors associated with the decline in hedgehogs across agricultural Britain). Data collected from scientists, coupled with that provided by the general public -- in the form of driver or gardener 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.
Fri Jan 06, 2012 12:51 pm