Lenni Sykes and Jane Durrant note, in their The Natural Hedgehog, that 80% of hedgehog admissions to the Welsh Wildlife Hospital in Llanddeiniol between 1986 and 1994 were due to manmade hazards; 18% were natural causes and 2% unknown. Similarly, in their Finnish study published in 2016, Anni Rautio and her team found that 75% of hedgehog carcasses they assessed had died from “human-related causes”. I know several hedgehog rescuers who consider anthropogenic impacts to far outweigh natural mortality in Britain’s hedgehogs, although I know of no empirical data to support this.
Perhaps the most obvious sign of the impact humans can have on the hog population can be seen on our roads. In 1999 Nigel Reeve and Marcel Huijser calculated that about 40% of hedgehogs treated by wildlife rescue centres in the UK and the Netherlands had been involved in road traffic collisions. Similarly, the vast majority (97%) of the hedgehogs classed as having died from human-related causes by Rautio and her colleagues had been killed on roads. In a short paper to Mammal Communications in 2016, David Wembridge and his colleagues reassessed the data on hedgehogs found dead on Britain’s road network and estimated as many as 335,000 are killed each year (see QA). Hedgehogs are most likely to be run over during the summer months, when they’re most active, but in London Pat Morris observed road casualties all year round. Similarly, in a 2014 paper to the journal Hystrix, Jorge Martinez and colleagues at the Centro de Recuperación de Fauna Salvaje noted that hedgehogs were brought into Spanish rescue centres all year around, albeit with a peak during the summer months.
As part of her Ph.D. research conducted at the University of Cork in Ireland, Amy Haigh generated some interesting data on how hedgehogs use roads, some of which was published in a paper to the journal Wildlife Biology in 2014. She radio-tracked a number of hedgehogs to try to assess their patterns of residency, movement and more general behaviour and, between April 2008 and November 2010, also surveyed 255 km (158 miles) of road around Cork City for hedgehog casualties. During the three years, 133 dead hedgehogs were recovered from the study area and a further 135 collected from roads elsewhere in Ireland. Almost two thirds (65%) of the casualties were males, with a peak in male fatalities between May and July, corresponding with the peak of the breeding season when males are moving widely looking for mates. Only in August did female casualties outnumber males, which the author suggests probably represents the end of the breeding season when females are moving around more trying to fatten up before hibernation.
More interestingly, Haigh’s tracking data showed that adult and juvenile hedgehogs of both sexes in County Cork entered fields and crossed roads at specific points. This suggests that it might be possible to direct mitigation activities (e.g. wildlife underpasses, warning signs or coordinating volunteers for ‘hedgehog patrols’) to maximum effect. If we can establish when and where hedgehogs are likely to try to cross a road, we can put measures in place to make it less likely they’ll get run over. Dr Haigh told me that her subjects tended to cross at the end of hedgerows.
The possible anthropogenic reasons for the observed decline in hedgehog populations are discussed elsewhere on this site (see QA), but sufficed to say cars are not the only human-related problem this species faces. Garden strimmers and lawn mowers kill many hedgehogs each year (although numbers can only be guessed at), while the removal of hedgerows and tidying of gardens reduces suitable habitat for them. Similarly, the widespread use of pesticides has probably led to a decline in their insect prey and/or the toxification of their main food sources, although studies are sorely lacking.
An additional manmade threat to hedgehogs exists in the form of discarded litter, particularly certain tin cans and yoghurt pots. It has been widely reported that hedgehogs, owing largely to their curiosity and gluttony, can easily get their noses cut on the sharp edges of tin cans – I have cut myself on both the lids and the inside rims of such cans on more than one occasion and have no doubt as to the damage they could do to the sensitive snout of a hedgehog.
Hedgehogs can easily become caught in some types of yoghurt pot. My own experience of this will remain with me forever, not least owing to the perplexed look on the face of a local fox bemused by the sight of a hedgehog with a pot on its head. A more detailed description of the event can be found elsewhere on this site (see QA), so I will summarise the relevant points. I was awoken in the early hours of the morning to find a hedgehog with a McFlurry® pot (the container of choice for fast food chain McDonalds’ ice cream dessert) wedged firmly on its head.
Upon going outside, I was able to easily catch the hedgehog in a towel and literally unscrew the pot from its head. The hog huffed, puffed and made various grunting noises in disgust at having been manhandled by yours truly, but upon removing the pot and putting it on the ground the animal scurried off into the bush; it had gone by the time I checked on my way out to work, so I assume it survived its ordeal. For those who have never seen a McFlurry pot before, they’re about 15cm (6 in.) tall and 9cm (3.5 in.) at their widest, tapering slightly towards the bottom; the cup itself has a dome-shaped lid with a hole roughly 5 cm (2 in.) in diameter, leaving a rim approximately 1cm (just under half-inch) wide. The hole is perfectly large enough to allow a hedgehog to stick its head in to get at the remaining sugar solution, but the spikes get caught on the rim, preventing the hog from getting back out.
Despite some rather amusing aspects to the above encounter, the threat posed by the McFlurry pot is not an insignificant one. I have no doubt, given the difficulty I had removing the pot, that had I or some other person not intervened, the hedgehog would never had got the pot off its head. The pot would prevent the hedgehog from eating or drinking and would ultimately lead to the animal’s death. Indeed, the McFlurry pot seemed such a significant threat to hedgehogs, and public opinion so strong, that a campaign by the British Hedgehog Preservation Society and Scottish Society for the Prevention of Cruelty to Animals caused McDonalds to agree to look into redesigning the packaging in 2002. Following four years of research, in August 2006, hedgehog lovers bore witness to the release of the new-look McFlurry containers. McDonalds announced that they had reduced the size of the hole in the lid to prevent hedgehogs getting their heads into the pots in the first place.