New research into hedgehogs injured by robotic lawn mowers discovers a significant but solvable animal welfare and conservation problem

Scientists from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) analysed 370 documented cases of hedgehogs being injured (cut) by electric gardening tools in Germany. Almost half of the hedgehogs found between June 2022 and September 2023 did not survive the injuries. The data reveal a serious animal welfare and conservation issue for these specially protected animals, as most hedgehogs were only found hours or even days after the accidents. In two further studies, an international team of scientists analysed how hedgehogs behaviourally respond to an approaching robotic lawn mower. The observed behavioural responses were used to develop a scientifically sound, standardised safety test to protect hedgehogs for robotic devices. The three scientific papers are published in the special issue “Applied Hedgehog Conservation Research” of the scientific journal “Animals”.

Since September 2022, the Leibniz-IZW has collected reports of hedgehogs with injuries caused by cuts from electric gardening tools via a closed Facebook page in collaboration with hedgehog rescue centres. The cases are becoming more frequent, placing an enormous burden on many hedgehog rescue centres and tying up important resources, as the injured hedgehogs often require an above-average amount of care and treatment. Almost half of the animals found and reported (at 47%) did not survive the injury, but had to be euthanised or died during care.

“The analysis of the 370 cases reported across Germany showed that there is not a single day of the week on which hedgehogs suffer cuts particularly rarely or particularly often. This is a clear indication that robotic lawn mowers – whose sales figures are increasing year on year – are often the cause of these injuries, as these devices are the only ones that can legally be used on a Sunday”, says Dr Anne Berger from the Leibniz-IZW, who led the scientific study. The rescue centres also report a steady increase in the number of cases of injured hedgehogs, which indicates a growing conservation problem in the context of declining hedgehog populations in Germany. “On the one hand, we suspect that a high number of cases of injured or deceased hedgehogs are not even found or unreported”, says Berger. “On the other hand, the analysis of the reported cases demonstrates a considerable animal welfare problem, as at least 60 per cent of hedgehogs with cuts were only found days or in some cases even weeks after the accident and therefore had to endure considerable suffering, pain and harm over a long period of time. Such suffering of animals is prohibited by law, provided there are alternatives that do not cause suffering.”

Together with international colleagues, Berger carried out two further research projects that could advance the development of alternatives to current robotic tools and solve the animal welfare and conservation problem. Earlier scientific investigations had already shown that – contrary to the claims of many manufacturers – robotic lawn mowers are unable to recognise small animals such as hedgehogs and usually cause serious injuries. A key factor in this process is therefore, among other things, how the hedgehogs themselves behaviourally respond to the robotic mowers. “Hedgehogs are shy and live hidden from us, but they are often also curious. We wanted to investigate this in more detail and carried out experiments with a total of 50 hedgehogs and a robotic mower with the cutting blades removed, which was never allowed to come into direct contact with the hedgehogs”, says Sophie Lund Rasmussen from WildCRU, University of Oxford and Aalborg University, who led this study. The hedgehogs showed seven different behavioural and positioning patterns during encounters and could be classified into “shy” and “bold” hedgehogs. “Adult hedgehogs tended to react more shyly. Also, the tested hedgehogs generally behaved less boldly when they encountered a robotic lawn mower for a second time”, says Rasmussen.

These findings were incorporated into the concept for a standardised hedgehog safety test for robotic mowers, which was developed by Rasmussen, Berger and the team. They analysed how 19 commercially available robotic mowers reacted to hedgehog carcasses. “Our results show that some models can injure hedgehogs, while others are harmless to them. Apart from one single incident, all robotic mowers had to physically touch a hedgehog carcass to detect it”, summarise Rasmussen and Berger. Smaller hedgehogs proved to be considerably more vulnerable. Based on these and other findings from the experiments, the team developed a test protocol that should eventually lead to the production and approval of hedgehog-friendly robotic lawn mowers that pose no hazards to the animals. The team advocates the mandatory introduction of such a test protocol at the European level by the European Committee for Electrotechnical Standardisation (CENELEC), thus reducing the chance of injuries of hedgehogs and enabling evidence-based consumer education.

According to the scientists, this research shows that alternatives to the use of current robotic mowers are technically feasible that do not entail animal suffering. In addition, political measures such as a ban on night-time operation for the devices should be implemented and more educational work carried out. This is because, in contrast to other electric lawn mowers, robotic mowers are allowed to be also used at night, on Sundays and on public holidays because of their low noise emissions. Unsupervised operation at night is particularly dangerous for hedgehogs, as they are nocturnal and do not run away from danger, but remain stationary and as quiet as possible. If they are run over and injured by the robots, they will – if they still can – silently seek the protection of hedges and bushes so as not to attract the attention of predators, for whom they would then be easy prey. Unfortunately, even minor cuts can later lead to severe inflammation or the laying of fly eggs in the wounds and thus, if left untreated, to death.

The population of hedgehogs – more precisely the European hedgehog (Erinaceus europaeus), also known as the Western European hedgehog or common hedgehog – is declining. The hedgehog was placed on the early warning list of the German Red List in 2020. In 2024, the hedgehog was named Wild Animal of the Year by the German Wildlife Foundation.