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Towards solving some prickly problems with hedgehog conservation

A talk to the Berkshire Mammal Group and EEG by Dr Phil Baker,
School of Biological Sciences, University of Reading, 5 April 2018

Dr Baker explained that the threat to hedgehogs and the need for their conservation had gone 'under the radar' until fairly recently, and now students of this creature were 'playing catch-up'. He argued that, as conservationists, we don't have the data we now need to establish scientifically how things have changed. He undertook to set out what we need to know; to establish if there is a decline in numbers and to quantify how much that decline might be; to identify what has caused it and what we need to do to conserve this culturally important species. Phil hinted at controversy, referring in passing to the problems of the human introduction of hedgehogs to island ecosystems, and warned he would be playing Devil's advocate. Indeed, as a clue, a couple of his many splendid photographs had humorously been annotated with red horns!


hedgehog First he defined the hedgehog as an insectivore, belonging to one of four groups that comprise the shrews, moles, solenodons and hedgehogs. Of the latter there are 16 species and the talk would be concerned with the West European Hedgehog (though Phil conceded the best hedgehog photographs were those of the African Pygmy Hedgehog.)

Anatomically modern hedgehogs have been found dating from the Miocene - five million years ago - so, when there were no hedgerows! We assume they were edge roaming, perhaps even woodland dwelling. ("Perhaps I should drop my aitches and call them 'edge'ogs'", Phil joked.) It is we who have changed the landscape and affected hedgehog behaviour and abundance.

The problem

Hedgehogs of the early modern period, c1600-1800, have been studied extensively by Roger Lovegrove (2007). He examined church records for evidence of animals killed by way of pest control. It was thought by some at the time that hedgehogs would drink milk direct from cows' udders and steal the yield. However, Lovegrove concentrated on records from ten just counties in southwestern England, concluding that half a million were killed over this period.

In the nineteenth century the human population doubled twice: 9m in 1801 to 38m in 1901. Moreover, during this period game shooting became large-scale and more organised. Gamekeepers were employed in considerable numbers, falling back only after the outbreak of war in 1914. Gamekeepers would kill anything that represented a threat to game bird production: foxes, wild cats, pine martens, stoats - even moles! Certainly hedgehogs were included for their likely predation of eggs, or even chicks. The oldest data sets we have date from the 1960s, and these reveal declining numbers of hedgehogs killed on game estates. But there is much less intensive pest control surrounding these estates, so killing predators locally creates a sink effect, with new animals moving in to vacant territories. Changing trap standards represents a threat too. Stoat traps will also kill rabbits and hedgehogs. A study in 2000 indicated they accelerated bi-catch, so the apertures of these traps were narrowed, causing a 75% reduction in kills. But such killing is no longer reported, and how can conservation work if one key group is silent? New self-setting traps from New Zealand have now been introduced and are deemed legal. These will become a threat as they catch animals repeatedly and without human involvement. There is bound to be an effect as stoats' and hedgehogs' heads are the same size!

Food shortages and rationing in the Second World War led to another cycle of threat. Farmers were encouraged to maximise food production; hedgerows were grubbed out to aid the efficiency of mechanisation; machines caused soil compaction and a reduction of earthworks abundance; chemicals reduced the number of invertebrates; even rodents were affected. These conditions have caused a reduction in biodiversity across all taxa - similar declines have been reported for flying insects and birds.

The road network has increased by a third since 1950 (especially with 'A' roads and motorways), and this has been accompanied by an increase in overall traffic volume.

Interestingly, the badger population, despite persecution and TB culls, has doubled over this time; the number of setts has increased 95% since 1985 and individual groups may also be bigger. But a study by Dave McDonald at Wytham Wood, having looked at pre- and over-winter conditions, indicates the adverse effects of climate change on food. It is much the same for hedgehogs. They have endured a 60-year onslaught!

How bad is it?

hedgehogThere have been several (though surprisingly not many) studies of hedgehog abundance and distribution, of which perhaps the best known was by Pat Morris in London in the 1980s. The classic work, however, was by Maurice Burton, a newspaper journalist in the 1950. Burton estimated from personal observation that in Oxfordshire there was one hedgehog per acre, so perhaps 30m hedgehogs in the UK. This is the questionable backdrop against which more recent surveys have been set.

Distribution was studied by Arnold (1993), but, like later studies, was dependant on the voluntary submission of data.

Steve Harris (1995) at Bristol mined the literature for published mammal surveys and estimated population numbers to 1km squares per land class. He allocated a score to each: 1, 'excellent' to 5, 'very poor'. There were only four studies of hedgehogs to draw upon, and the results spread over 20 land classes. Harris estimated one and a half million individuals, and rated hedgehogs 4: 'poor'. This work revealed just how much we did not know. And Defra's recent updates suggest there has been no progress. There are massive gaps in in our knowledge of population and habitat.

The oft-quoted figure of a 90% crash between the 1950s and 1990s suggests - contentiously - that hedgehogs are worse off than tigers! But not everything is as it seems. Burton himself used the caveat, "highly unlikely" when arriving at his headline figure, and in Germany the estimate is a considerably more conservative one hedgehog per 25 acres. It is generally believed there has been a decline, but almost certainly not by as much as the quotations suggest.

We need monitoring programmes, Phil argued, such as those conducted in Hyde Park with thermal imaging equipment, but the cost usually forces us to use alternative means. There have been several ongoing crowd-sourced surveys in recent years, such as those by the People's Trust for Endangered Species in London and the British Trust for Ornithology in East Anglia:

Mammals on Roads One a year, reporters drive their usual routes. 3% decline since 2002
Living with Mammals Garden survey by PTES.2% decline since 2004
Garden Birdwatch Mammals are an optional inclusion. 2% rise since 2007

Likewise the Breeding Bird Survey from 1996, for which volunteers walk a transect twice a year. However, these are very partial, reliant on the self-selecting involvement of volunteers and partial submission of records, with no randomisation of samples and no standardisation of effort.

Take the counting of squashed hedgehogs on roads. How does the number reflect population and vulnerability to traffic? Is it true that the more casualties, the bigger the total population must be in proportion; or conversely, that the population must have suffered a decline due to increasing attrition? This becomes more complicated when one realises that, according to a Dutch study, hedgehogs actively avoid roads. Such evidence is borne out by further work at Southampton by Rondini and Doncaster (2002). Also, the access to the evidence is transient as carcasses disappear quickly and so is difficult to verify or even quantify.

Finding an effective technique

hedgehogTo make matters worse, however imperfect the evidence, the conclusions of these various surveys are inconsistent and even contradictory. They simply don't tell us the same things or even present a coherent trend. While most indicate decline, one (urban) survey suggests increasing numbers. What we need, Phil argued, is a robust technique allied to randomness of application so as to avoid the effects of recorder bias. Equipment should be accurate, cheap and verifiable if it is to keep the public engaged and allow widespread effort.

As gauging absolute numbers appears to be impossible for the present, let's settle for presence/absence. For this the hedgehog tunnel has been developed, allowing the capture of footprints in ink. However, we must also be aware of false absence; if we have no evidence of presence, how do we know if hedgehogs are not there? We may simply have missed them. How much is apparent absence down to animal distribution and have much to inaccurate technique?

One technique (Williams et al) is to work on a site that is under the management of one person alone. Ten tunnels are set out and checked repeatedly over five days. Tunnel locations are sited appropriately, though it is accepted that the reliance on edges is an assumption. In the reference survey 261 volunteers took part in monitoring rural sites - one of the biggest citizen science projects - while 219 volunteered for urban sites (in Reading). In the latter there was a 32% success rate in 2013 and 40% in 2014.

The urban study in 2013 indicated a 60% chance each day that hedgehogs would be present over the week; and in 2014, 68%. It revealed a tendency for hedgehogs to return each day and suggested that, if a tunnel was in a garden, they'd find it. Indeed, there was a 78% consistency of use. Conversely, if you don't get inky paw prints, it is because the hedgehog isn't in the garden. When homeowners where asked if they thought they had hedgehogs, or to predict their presence, 35% got it wrong. Indeed lots of residents thought there were very few in the Reading area, whereas Lower Earley actually has a good population.

Phil expressed himself satisfied with the technique for garden monitoring; it is certainly better than householder perception.

Impact of badgers

Badger sett density has a negative impact on hedgehogs - whereas houses appear to have a positive effect! After you've accounted for badgers, there are few impacts of significance. Badgers affect hedgehogs like nothing else does. Just how bad for hedgehogs might they be?

Actually, this is a more widely studied field, with three studies as a result of the government-sponsored badger cull alone! Hedgehogs don't tolerate badgers, so after the cull their numbers increased. Objectively, the lesson is clear: "fewer badgers; more hedgehogs". Hedgehogs are more present in urban areas than rural, a pattern that reflects badger distribution. Hubert et al (2011) studied the indirect evidence of food supply and concluded that hedgehogs avoid badgers by moving into town, where, coincidentally, people will also feed them!

Why are badgers a problem for hedgehogs? Eagles apart, badgers are the most likely source of predation, though no studies have been carried out on the direct effect of predation on the overall hedgehog population. More importantly, they compete for the same foodstuffs. One badger can eat as much as seven hedgehogs can. However, it is not the case that total food supplies have dwindled, as there has been sufficient to support an increase in badger numbers.

Humans have altered the rural landscape and unintentionally made the problem of predation and competition worse. Historically they co-existed after all. Gardens, however, represent a refuge from both. The challenge is to find sites that allow co-existence. Trading badgers for hedgehogs would be a 'hot potato', as the reaction to Phil's earlier comments by some members of the audience made only too clear!

Planting more hedgerows would be one answer, but that would cost large sums and having to record multiple sites to get the supporting information. Then farmers would have to be funded in order to make change viable. It would undoubtedly be expensive.


hedgehog Over-wintering behaviour has been studied in Sweden, where 25% to 40% of hedgehogs die each year. In the UK, survival rates are better: 18%-21%. The University of Reading has studied hibernation at locations near student accommodation in Gloucestershire and Nottingham, using radio tagging. The research has revealed multiple nests, nest movement, moving around a lot before hibernation - but also two or three moves during the period of deep sleep. In one of the studies, 22 animals used an average of 6.5 nests. Good nest sites are required for security, cover, warmth and the abundance of nesting materials. Hedgehogs like to have options, to be able to move if needed. Good quality hedgerows, woodland and brambles offer the best bets. If they get too cold (-5oC to -10oC) they will have to wake up, so climate change is a potential problem as well. Perhaps the urban heat island effect is another reason for the perceived increase in preference for urban locations?

Fragmentation by roads

Hedghogs need help with roads as the width of pavement and the speed and volume of traffic represent considerable challenges. Williams studied the effect of motorways for his PhD and tentatively came to the conclusion that they separated distinct populations that had little or no contact with each other. Populations are already patchy, with more places where hedgehogs are absent now than in the 1990s. And things are getting worse, as the Highways Agency installs solid concrete barriers rather than the old metal ones. The only viable crossings are bridges and underpasses - or purpose-built badger tunnels which come with an inherent danger! But even urban roads are a challenge.

Prospects, especially in town

Suffering poor, fragmented habitat and threatened by badgers, no wonder hedgehogs are heading for the towns! The only 'good news' for hedgehogs is the badger cull. (Interestingly the hedgehog hotspots are East Anglia, with a tradition of gamekeeper control of badgers and Yorkshire, with a tradition of badger-baiting.) More hedgerows are vital, but expensive. In the short term we can at least help the urban hedgehog.

It has been suggested that foxes pose a problem and indeed when the foxes of Bristol were suffering from mange a few years ago, hedgehogs appeared more numerous. However, although there have been a hundred studies of foxes' diet, hedgehogs feature very infrequently. And dogs tend to be indoors at the times hedgehogs are out and about.

We can provide sources of food (but should not offer cow's milk or mealworms), shelter and access. All sorts of threats can be moderated: litter, fences, rat boxes, bonfires, rubber bands. Decking is not good for food supply, though it is a good source of shelter. Phil noted that gardening and maintenance practice does make a difference. Ten years ago, you'd find plenty in the Harris Garden between 9-12pm, but not since the refuges have been systematically mown. As for holes in fences, 48,000 people have signed up to Hedgehog Street. According to the Earley gardens project (Piper 2016), we locally could do better!

If we double the access, we double the number of hedgehogs. There is no obvious difference in the gardens used. On any one night, a hedgehog might use eight gardens; a female might cover an area of 100m x 100x, or more if mating. So why not use all the gardens available? Is fear a deterent? We need to radio-track to see whether they use different gardens on different nights. Hog boxes - of which there are dozen of designs - are more likely to make a garden attractive, especially if placed nearer the house! It might take time, for although hedgehogs make repeat visits, their pattern of travel will change from year to year.


  • We are at a moment of crux; hedgehogs are declining throughout Europe and soon to be reclassified as 'near threatened'.
  • We are now getting the data we need and urban areas are increasingly recognised as important.
  • Difficult decisions have to be made; it's in our hands, but we need buy-in from farmers and householders. Funding will be vital to make any wider scale difference.

Summarised by Edwin A.R. Trout


Phil had promised to be provocative and play the devil's advocate, and certainly prompted reactions from the floor on a number of occasions during his talk. Where possible, the subject matter of interjected questions has been incorporated into the foregoing account, but there were several others on additional topics, as answered below.

Over the past 10-15 years there has been an upswing in the study of hedgehogs. However, there have been only two studies of diet since the 1970s. There have been no studies of the impact of deer on the density of woodland vegetation, though the question prompted an interested response.

The rehabilitation of injured hedgehogs provides a valuable function, except where the release occurs in an area remote from the hedgehogs' home territory.

'Tip-ex surveys' are a useful way of monitoring the number of individuals in a local population, thought this has raised concerns about the possible need for training and licensing in wildlife handling.

Do hedgehog have fleas? No, not to any significant degree.

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