Researchers develop hedgehog safety test for robotic lawnmowers

Their aim is to establish a certification system, enabling consumers to select 'hedgehog-friendly' lawnmowers, thereby safeguarding these cherished mammals.

The popularity of robotic lawnmowers is on the rise. Yet, there is a growing concern regarding their operation, particularly at night, which coincides with the peak activity time for hedgehogs. The European hedgehog population is experiencing a sharp decline due to various factors, including habitat loss, traffic accidents, intensive farming, and injuries from dogs and garden equipment. Notably, hedgehog rehabilitation centres have seen an increase in injuries attributed to robotic lawnmowers.

Dr Sophie Lund Rasmussen from the University of Oxford, also known as 'Dr Hedgehog', emphasised: “There is an urgent need to identify and phase out models of robotic lawnmowers that pose a threat to hedgehogs. Our new standardised safety test will greatly aid hedgehog conservation, by enabling manufacturers of robotic lawnmowers to ensure their models are ‘hedgehog friendly’ before they are put on the market.”

Inspired to create this test after conducting collision experiments between robotic lawnmowers and deceased hedgehogs, Dr Rasmussen observed: “All the robotic lawn mowers I tested had to physically touch the hedgehog in order to detect it, and some did not even detect the dead hedgehog. In mild cases, the robotic mower would lightly nudge the hedgehog then change direction, but in the worst-case scenario, the machine ran straight over it with the blades still running, causing extensive damage to the hedgehog carcass.”

The novel safety test employs specially crafted hedgehog 'crash test dummies' to ascertain a robotic lawnmower's ability to avoid real hedgehogs and the extent of damage in the event of a collision.

In pursuit of realism, the researchers collaborated with a Danish hedgehog rehabilitation centre to understand how rehabilitated hedgehogs, ready for release, react to robotic lawnmowers. They observed fifty hedgehogs' responses to a deactivated (bladeless) mower in a controlled environment. The hedgehogs demonstrated three primary reactions: fleeing, freezing partially curled up, or curiously inspecting the mower. Younger hedgehogs tended to be bolder than their adult counterparts.

Dr Rasmussen noted: “Each hedgehog was tested twice and, interestingly, they tended to act more shyly on their second encounter. This is hugely important, since it suggests that hedgehogs may learn from their first encounter with a robotic lawnmower. Potentially, if a hedgehog survives its first encounter with a robotic lawnmower, it is less likely to be injured in the future because this may cause it to avoid them. So, the more hedgehog friendly mowers out there, the more chance there is that the first mower a hedgehog meets is a hedgehog friendly one. If these hedgehogs meet a mower again later in their lives, they will then likely be more cautious.”

Using these observations, the researchers determined the optimal positions for the crash test dummy, designed based on the initial collision tests, and made of a soft, rubbery plastic to mimic a hedgehog's body composition. They plan to publicly release the dummy design for 3D printing, assisting robotic lawnmower companies in developing hedgehog-friendly models. Ultimately, they aim to integrate the hedgehog safety test into official European testing protocols for robotic lawnmowers, potentially leading to a certification scheme for 'hedgehog-friendly' models.

Dr Rasmussen added: “A key first step is to improve the sensors, so that they detect the hedgehogs and avoid them. Developing additional technologies such as camera recognition could eventually allow the robotic lawn mowers to detect hedgehogs at a distance and change direction before they get close. It is also important that the blades of the mowers are pivoting, so that they fold away under a protective surface when hitting something harder than grass.”

Dr Stephan Meyer, R&D manager at STIHL and a member of the project team, shared: “STIHL highly values the effect of these findings on the development of robotic lawn mowers, and we are using the learnings from this interactive project to improve the situation for people and animals. The results of the studies will form the scientific basis for the development of a safety standard to protect hedgehogs.”

A spokesperson from Husqvarna, a manufacturer of robotic lawnmowers, stated: “At Husqvarna we have a 30-year-old history in robotic lawn mowing and safety has always been our top priority. We were early to introduce the light-weight pivoting blades, which research has proven to be more ‘hedgehog-friendly’. Today, technology is moving faster than ever and all learnings we can get from the research conducted by Dr Rasmussen and her team will help us develop functions that will even more help to cater for keeping wildlife safe in our home gardens.”

Owners of robotic lawnmowers can contribute to hedgehog safety by checking for hedgehogs before using the mowers and operating them during daylight hours, as hedgehogs are mostly nocturnal.

Co-author Dr Anne Berger from the Leibniz Institute for Zoo and Wildlife Research in Germany, who has researched hedgehog injuries from robotic lawnmowers, commented: “Cut injuries from robotic lawnmowers are placing an enormous burden on many hedgehog care centres and using up important resources, as these injuries often require above-average care and treatment. Moreover, the majority of hedgehogs with cut injuries are found days or weeks after the accident happened and therefore have to endure considerable suffering, pain, and harm until they are found. The development of ‘hedgehog friendly’ models could therefore help prevent a considerable amount of animal suffering.”

Fay Vass, Chief Executive at the British Hedgehog Preservation Society, expressed: “We are pleased to have been involved in funding this important piece of research. The population decline of hedgehogs is alarming and unsustainable, so it is crucial to find out which potential dangers are actually causing problems, and which are not. We can then focus our efforts on issues that are impacting on hedgehog numbers to help minimise the threats against them. Hopefully, the results of this work will stop or drastically reduce the risk of robotic lawnmowers causing harm to hedgehogs.”

This research, aligning with the CENELEC protocol EN 50636-2-107 for the safety of household and similar appliances, signifies a significant step in hedgehog conservation. The protocol, established by the European Committee for Electrotechnical Standardization in Brussels, Belgium, in 2015, sets the framework for the development and approval of robotic lawnmowers in the European market. The integration of these new findings into the protocol could greatly enhance the protection of hedgehogs, contributing to the survival of this iconic species.