DEAD hedgehogs were 'badly mutilated' by robotic lawn mowers in a study to reveal technology's impact on hedgehogs and make gardens safer.

Robotic grass cutters running at night may threaten the lives of hedgehogs roaming in gardens as a new study reveals inconsistency between brands and models. 

Research by Dr Sophie Lund Rasmussen, who is known as Dr Hedgehog due to work in hedgehog ecology, and colleagues from Oxford University and Aalborg University show that different models of robotic grass cutters vary substantially in their capability to detect and avoid hurting hedgehogs.

The team tested 18 models of robotic lawn mowers in collision tests with dead hedgehogs - some of which were 'badly mutilated'.

The dead hedgehogs in the study were collected from hedgehog rehabilitation centres, where they had been too poorly to save.

Each robotic lawn mower was tested 12 times; with four dead hedgehogs representing four different weight classes, each tested in three different positions.

According to the study, certain technical features significantly improve the mowers’ safety index.

Dr Rasmussen said: “It is important to discover and document what is causing the horrific injuries we see inflicted on hedgehogs every year so that we can improve the conservation initiatives directed at this declining species.

"We already knew that garden strimmers and dog bites unfortunately are the causes of numerous injuries to hedgehogs, but we didn’t know if the robotic lawn mowers were also a problem."

The results showed that some models of the grass cutters caused extensive damage to the dead hedgehogs in the tests, but there were 'noteworthy' differences in the degree of harm inflicted, with some machines consistently causing no damage.

Dr Rasmussen added: “I was very surprised to discover how differently the robotic lawn mowers performed in our tests. It was devastating to witness how some models badly mutilated the dead hedgehogs. But at the same time, other models did quite well, and did not seem to harm the hedgehogs."

None of the models could detect the hedgehog cadavers until they bumped into them, and none of the robotic lawn mowers tested were able to detect the presence of dead, dependent juvenile hedgehogs, which weighed less than 200g.

Technical features such as pivoting blades, skid plates and front-wheel drive significantly increased the safety index of the machines, making the machines less harmful to hedgehogs.

Researchers hope the research will encourage hedgehog conservationists and mower manufacturers to work together and make hedgehog-friendly garden technology.

Fay Vass, chief executive of the British Hedgehog Preservation Society, which funded the study, said: “This is important work that we are pleased to be able to support. We needed to find out for sure if these mowers were in fact harmful to hedgehogs.

"Hopefully now we have this information we can offer advice to industry on producing hedgehog safe mowers and to the public on how best to help hedgehogs when caring for the lawn.

"In the meantime, we would suggest people refrain from using these machines at night (from dusk to dawn) when they are more likely to encounter hedgehogs.”

The organisation says hedgehogs are nocturnal but might occasionally be active during daytime for example if their nest has been disturbed, a mother hedgehog is collecting nesting materials or if they are poorly or injured and in urgent need of help.

The research comes ahead of Hedgehog Awareness Week next month, from May 2 to 8, 2021.