Briefing Sheet: Badgers and hedgehogs

Species background

Hedgehogs

European hedgehog (by Alma, licensed under CC BY-SA 3.0)

European hedgehogs are unmistakable. Small, nocturnal mammals native to the UK1,2, they live in woodlands, field borders, hedgerows, and suburban habitats – but are typically habitat generalists3,4. They are generally active from April to October/November5, hibernating through winter and early spring when food is less available6. They are protected under multiple pieces of legislation, including the Wildlife and Countryside Act, 1981 and Wild Mammals Protection Act, 19967.

Hedgehogs are opportunistic feeders8,9 and can travel 1-2km a night looking for food10. They have a wide diet consisting mainly of invertebrates, commonly hunting for slugs, earthworms, millipedes, earwigs, beetles, caterpillars, and sometimes fruits and mushrooms2,3,10

Unfortunately hedgehogs have experienced severe declines and are now classed as vulnerable and of conservation concern in the UK11, thought to occupy just 22% of rural landscapes in England and Wales12. There were an estimated 30 million hedgehogs in the UK in the 1950s1 but by 1995 numbers were thought to have fallen to just 1.5 million. Based on data from recent surveys (such as the People’s Trust for Endangered Species ‘Mammals on Roads’ survey, which began in 200113), estimates from 2016 suggest that there are just 522,000 hedgehogs left in the UK14. That said, since 2012 fewer urban hedgehog sites have been lost, and where populations have persisted hedgehog numbers appear to be growing13,15.

Badgers

Badger in a garden. (by Chris P, licensed under CC BY 2.0)
Badger in a garden. (by Chris P, licensed under CC BY 2.0)

European badgers are charismatic, medium-sized mammals native to the UK16,17. They are generally nocturnal but are also active around dawn and dusk18 and can be active throughout the year as they do not properly hibernate, instead going into a type of rest called torpor – waking in milder weather to find food17.

Badgers are well known as the UK’s largest land predators, but they are actually opportunistic omnivores – feeding on items such as earthworms, snails, slugs, amphibians, birds eggs, cereals, and soft fruit like blackberries19,20. Badgers can also hunt small mammals such as rodents and hedgehogs, but these make up a small proportion of their overall diet21-23. Earthworms provide both water and protein24 and are the most important food source for badgers4, making up anywhere from 54% to 89% of badger diets21,25.Living in large social groups in communal burrows called setts18, badgers occupy broadleaved woodlands, open pasture and fields, gardens, and embankments17. They are generally more abundant in the south of England due to the greater availability of hilly landscapes and broadleaved woodland4. Recent population estimates from 2018 suggest that there are around 562,000 badgers in the UK14, all of which are protected under the Protection of Badgers Act, 1992 and Wildlife and Countryside Act, 198120. It is estimated that there was an 88% increase in badgers in England and Wales when comparing survey data from 1985-1988 and 2011-201326.

The relationship between hedgehogs and badgers

The habitats that badgers and hedgehogs inhabit in the UK overlap greatly9,12. They also share very similar diets and foraging grounds3, with both species maximising their consumption of prey items like earthworms24,27. Badgers are also what are called ‘intraguild predators’, meaning that they not only compete for a lot of the same prey as hedgehogs, but can also hunt hedgehogs themselves when other food is scarce28,29.

Although species such as foxes and domesticated pets are known to attempt to eat hedgehogs13, badgers are the main predator of hedgehogs in Great Britain2,30,31. This is because they are the only species believed to be able to manoeuvre and prise open hedgehogs when they roll into a defence curl32,33.

Do badgers drive hedgehog declines?

There is a range of evidence that suggests that the abundance of badgers has a negative effect on the presence and abundance of hedgehogs31,32, particularly on a local scale28. This conclusion was reached by studies looking at roadside wildlife sightings and deaths34 and using experimental evidence from randomised badger culling trials. The latter suggested that in areas where there was suitable habitat, hedgehog numbers more than doubled over five years when badger numbers were controlled35. In contrast, there are several studies that state that badgers and hedgehogs can live alongside each other9,12, with hedgehogs and badgers often observed finding food in the same areas without hedgehogs showing signs of predator avoidance3 or changes in habitat selection or use36,37.

There is some evidence which suggests that badgers may manage hedgehog numbers in rural areas38 and that hedgehog occurrence is more likely as the distance from badger activity increases39, seeming to avoid areas with higher badger densities and occupying more urban areas12,30,33. One study by Hof, Snellenberg and Bright (2012) found that the mean distance from edge habitat – such as near hedgerows or the borders of woodlands – that hedgehogs ventured was 7m when badgers were present and 27m when they were absent, indicating that hedgehogs tend to keep closer to shelter when in areas with badgers present and may live in a ‘landscape of fear’9,36,40. That said, suggestions that hedgehogs occupy more urban areas because they are often badger-free could be the result of hedgehogs utilising easily accessed pet-food, rather than because they are trying to avoid badgers39,41.

In addition, there is also some evidence of hedgehog numbers being negatively related to badger sett density, with some studies citing a strong negative relationship between the two12. Other studies suggest that proximity to badger setts may have a strong negative effect on hedgehog reproductive success41. While there may be a relationship between hedgehog numbers and the number of badger setts, it is important to note that sett density does not translate directly to the number of badgers, making it a poor indicator of badger abundance28. Research by Williams et al. (2018) found that hedgehogs only occupy around 22% of rural areas in England and Wales, and are absent from 71% of sites that do not have badgers12, suggesting that badgers are not the main factor impacting hedgehog populations.

Some studies have found evidence of badgers consuming hedgehogs in the UK and throughout Europe, but few have reported predation21,28,42,43. Documented evidence varies, with cases including four hedgehogs being consumed by a single badger found dead in England in the 1930s44; to 11.2% of collected badger scats containing hedgehog remains across three sites in Poland through 1986-94 25; and two out of 69 badger stomachs assessed in Italy between 1996-1998 containing hedgehog remains45. Although there is lots of evidence to suggest that badgers do occasionally predate hedgehogs, this only makes up a small proportion of hedgehog deaths compared to other factors such as road-traffic accidents37,46. A study from 2017 found that of 78 hedgehogs detected, eight died – only one of which was suggested to be the result of possible badger predation36. Similarly, a study in 2011 recorded only one case of badger predation despite regular sightings of badgers in the study area, with the remaining 23 hedgehog deaths recorded attributed to factors such as dog attacks, road traffic accidents, and illness37.

A more complicated picture

The question of whether badgers drive hedgehog declines is not simple, and as with many things in the natural world, depends greatly on the context. As badgers and hedgehogs share lots of the same habitats and food sources, there is certainly opportunity for competition and conflict, but correlations and trends do not imply cause27.

Lots of studies point to badgers and hedgehogs being able to coexist across landscapes9,12,39. However, the role badgers potentially play in hedgehog declines is not clear or evidenced at a national scale28, with predation appearing to have smaller, local impacts at most – such that it is unlikely to drive population declines31. Studies show that incidence rates of badgers consuming hedgehogs is generally low across the UK and Europe21,25,42-45. It is also not accurate to characterise badgers as diet specialists or generalists, as their diet will reflect availability of food and alternatives, as well as learnt experience21,28. As a result, it is much more likely that predation is the result of low invertebrate availability, potentially causing more competition between the two species and leading to predation of hedgehogs3,4,28.

Higher numbers of hedgehogs in ‘badger-free’ areas also warrants discussion, as despite some studies stating that hedgehogs occupy smaller, urban or suburban gardens to avoid badgers30,47 the reality appears to be more complex. The availability of easy-access pet food and nest boxes make urban and suburban areas very attractive to hedgehogs13,41, and as competition for food can cost vital energy, it is logical that hedgehogs would seek out easy food37,48. Hedgehogs have been found to avoid badger odour, however this does not persist and is only a short-term effect37,49. Similarly they have been show to both avoid and prefer broad-leaved woodland – which is typically badger habitat – showing no consistent avoidance of typical badger habitats across different studies4,14,50.

A study by Trewby et al. (2014) that investigated hedgehog numbers through a five-year badger-culling cycle found that hedgehog numbers significantly increased in grassland areas. This result was initially suggested to be the result of changes in hedgehog behaviour due to reduced competition for food, but the finding was attributed to increases in hedgehog numbers – although it was not clear if this was because of reduced predation, or less competition for food, or both35. This uncertainty could have also been emphasised by the fact that detection rates can sometimes be low for hedgehogs, with many studies also having small numbers of hedgehogs to investigate51.

Other causes of hedgehog decline

Unfortunately, hedgehogs are threatened by several factors in the UK9, having been in considerable decline since the 1960s4,13,52. We should also remember that hedgehog decline data are largely based on extrapolated estimates sourced from citizen-science data, so it is difficult to create an accurate picture of decline34

Earthworm (by Luis Miguel Bugallo Sánchez, licensed under CC BY-SA 3.0)
Earthworm (by Luis Miguel Bugallo Sánchez, licensed under CC BY-SA 3.0)

Availability and accessibility of food is considered to be a determining factor for hedgehog distribution3, and as hedgehogs mainly consume items such as earthworms2, global declines in invertebrates pose a big problem for the species28. Earthworms in particular are sensitive to changes in temperature, humidity and soil moisture3, so could be vulnerable to the effects of climate change, affecting natural food availability for hedgehogs. They may also be sensitive to chemical pollution and/or poisoning53.

Over recent years more of the public have started to provide food for hedgehogs in their gardens, but the impact of this has not been researched thoroughly9 and initial studies suggest that this is increasing winter activity when hedgehogs should be hibernating9,54. This could be exaggerated by climate change, which could threaten the stability of hibernation for hedgehogs as winter temperatures increase55. Temperature-related food and winter nest availability are thought to be major factors influencing hedgehog populations and winter survival rates, with warmer summers and unstable winters likely to result in more hedgehogs failing to survive winter and/or entering wildlife care4,41. This is particularly concerning for the hedgehogs in urban areas, as they are approximately 2°C warmer than nearby areas of countryside41.

Movement of hedgehogs into more urban areas also has the potential to expose hedgehogs to weedkillers and pesticides through contact with treated plants and ingestion of prey such as slugs8,9 which can lead to poisoning51,56 and is known to have an accumulative effect on hedgehogs, with unknown impacts on populations28,56. This problem is not isolated to urban areas, with secondary poisoning – usually by eating poisoned food – being a long-term threat to both suburban and arable hedgehogs57. Slugs and snails are beneficial ‘decomposers’, but some species only consume plant matter and so can be pests for horticulture, field vegetables and arable crops58. They can be controlled using chemical pellets, which usually contain chemicals such as ferric phosphate, methiocarb or metaldehyde59,60. Metaldehyde is the active ingredient in 80% of globally used slug pellets and has been used since 1940s61, with agricultural use greatly increasing since 1990 and over 1,640 tonnes of metaldehyde used in Great Britain between 2008 and 201461.

These slug pellets are generally applied between September and December to autumn-sown wheat and oilseed rape crops, when slug pressures are at their highest62 and when hedgehogs are still active and building up fat reserves for winter. Metaldehyde has been found to move easily through soils and water, exposing and having adverse effects on earthworms and other soil invertebrates in the process53,61. Although some studies have shown that consuming poisoned prey does not appear to have an impact on hedgehogs63,64, particularly as they are unlikely to consume high enough levels of poisoned prey to have an effect in the wild65 – it remains that there is often no antidote to chemical poisons66 and metaldehyde is thought to be a big enough pressure on wildlife and environmental health to be banned for outdoor use from 1 April 2022. It is also important to note that even if molluscicide poisons found in slug pellets do not directly cause harm to hedgehogs, their wider impact on key prey items such as slugs, snails and earthworms is a concern for hedgehog food availability. 

Loss or fragmentation of habitat is another factor that is thought to have a large impact on hedgehog populations37. It is well known that hedgehogs are associated with hedgerows, field borders, arable land, woodlands, and urban or suburban gardens3,4,14,50. Loss or lack of healthy hedgerows51,67, intensification of agriculture, and disturbance create unfavourable conditions for hedgehogs, particularly with increasing ‘tidying’ that results in loss of shelter, nesting, and hibernation spaces and materials9. Despite increasing numbers of hedgehogs in urban areas, hedgehog presence is negatively related to built-up areas28. Even though gardens make up 22-36% of urban land cover68, gardens and surrounding habitats can become inaccessible through the addition of roads, railways, pathways and fences9,34,69,70. This can cause what is called an ‘extinction debt’, where previous habitat losses or population declines result in populations becoming isolated, eventually perishing if not supported9,71,72

Road networks add to this problem, and while some roads can offer small amounts of roadside habitat, most roads present a major barrier31 and are significantly avoided by hedgehogs70. Roads present several issues, resulting in habitat loss and fragmentation, increased disturbance, pollution, and death69,73. In the UK there are approximately 400,000km of roads, with around 9% considered to be ‘high risk’ for hedgehogs, equivalent to around 36,000km of road73. As hedgehogs can travel several kilometres a night, it is expected that they will often come into contact with some of these roads74. Recent studies suggest that between 167,000 and 350,000 hedgehogs are killed every year on roads75, accounting for 10-20% of annual hedgehog deaths in the UK46. This appears to peak in July and August when hedgehogs are most active, and when juveniles are leaving their nests75, supporting the idea that road networks can greatly affect hedgehog populations4

In addition to these factors, several other animals can have impacts on hedgehogs. Foxes, birds of prey, and domestic cats and dogs are all thought to disrupt or threaten hedgehogs to some degree4. Foxes are known to attack and attempt to predate hedgehogs occasionally, but are more likely to present competition for urban food sources34,39. Similarly, domestic cats and dogs are known to predate young or injured hedgehogs, as well as disturb adults76, with hedgehogs having a significant negative relationship with the presence of dogs4. As well as the actual animals presenting a threat to hedgehogs, they can also expose hedgehogs to unsuitable foods such as milk or high-fat pet foods10.

Hedgehogs are also known to be susceptible to a wide range of diseases and parasites such as ticks and lungworm2,9,28,77, although the impacts on populations is not well understood77.

Conclusion

Overall, despite experimental and small-sample evidence of predation in badger cull zones and on local scales, predation and competition from badgers is unlikely to be the main explanation for hedgehog declines nationally9. Badger presence can be an important factor in determining the presence or absence of hedgehogs on local scales, but factors such as good habitat and food availability are much stronger predictors of where hedgehogs will and will not occur28. Habitat loss and fragmentation, road networks, and climate change are major threats to hedgehogs and significantly impact hedgehog declines9, with road networks in particular resulting in great annual losses of hedgehogs46,75. That said, predation from badgers does occur and in order to more accurately assess the relationship between hedgehogs and badgers in the context of habitat quality, more research is needed36.

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