Robot Mowers and Hedgehogs: Wildlife Safety

The one rule that matters most: only run a robot mower in daylight. Hedgehog Street, the campaign run by the British Hedgehog Preservation Society and the People's Trust for Endangered Species, advises daytime mowing and checking the lawn before the mower starts.

Why It Matters

Britain's hedgehogs have declined sharply. The State of Britain's Hedgehogs 2022 report found rural populations had fallen by between 30% and 75% since 2000, with the steepest losses in eastern England, although urban populations appear to have stabilised. In 2020 the Mammal Society's Red List classed the British hedgehog as Vulnerable to extinction, and the European hedgehog has since been moved to Near Threatened on the global IUCN Red List.

Gardens matter for hedgehogs, and hedgehogs are mostly active at night, which is exactly when an unattended mower on a timer might be running.

What the Research Found

In a peer-reviewed study published in 2021, a team led by Dr Sophie Lund Rasmussen of Aalborg University and Oxford's Wildlife Conservation Research Unit tested 18 robot mower models. The work was funded by the British Hedgehog Preservation Society and used hedgehogs that had already died in rescue centres, not live animals. They found:

• Every model had to physically touch a hedgehog to detect it.
• None detected young hedgehogs under 200 g.
• Some models caused extensive damage, while others consistently caused none.
• Pivoting blades, skid plates and front-wheel drive all made a mower significantly safer.

Separate Oxford-led behavioural tests with 50 live hedgehogs and a disarmed mower with no blades found that hedgehogs either fled, froze partly curled up, or sniffed the machine. Younger ones were bolder. Curling up does not protect a hedgehog from a blade.

In 2024, Oxford researchers announced a standard hedgehog safety test for robot mowers using 3D-printed hedgehog "crash test dummies", supported by STIHL, Husqvarna and the British Hedgehog Preservation Society. It gives manufacturers a common way to measure the risk.

How to Mow Safely

1. Schedule daytime mowing only. Set your schedule to finish well before dusk, and do not use night mowing modes.
2. Check the lawn first, especially long grass and the edges of beds, where hedgehogs and amphibians shelter. The RHS gives the same advice for strimming.
3. Use no-go zones around hedge bottoms, log piles and compost heaps.
4. Ask the manufacturer about hedgehog safety features before you buy, as the RHS suggests. Cameras and LiDAR can help a mower spot obstacles, but none of the product pages we checked quote independent hedgehog test results.

Seasons to Be Most Careful

The RHS says hedgehogs hibernate from about October or November until March or April. From spring to autumn, while they are active, daytime-only mowing matters most. Our mowing calendar shows how much cutting each month needs, and winter storage covers putting the mower away during hibernation.

Other Wildlife

Frogs, toads and slow worms also shelter in long grass. Plantlife's No Mow May campaign asks gardeners to leave the mower off for May. You can do the same with a robot mower, or set a no-go zone over part of the lawn as a wildflower patch all summer.

When you set up a new mower, our setup guide covers schedules and no-go zones.