doodlerobots00GARDEN ROBOTS AND WILDLIFE
Robot mowers are good at grass. Hedgehogs are harder.
Hedgehogs are nocturnal, and robot lawn mowers are becoming popular in UK gardens. Researchers at the University of Oxford's WildCRU and in Denmark tested how well the machines notice a hedgehog, and the answer depended on the model.
When to mow01Principles
02THE SHORT ANSWER
The tests used hedgehogs that had died
of illness at rescue centres, not live animals.
THE CRASH TESTS
In a 2021 study of 18 robot mowers, every model had to touch a hedgehog to detect it. Some nudged it and turned away; others ran over it and caused serious damage.
See the numbersTHE HOGLETS
None of the mowers detected dependent juvenile hedgehogs under 200 g. Hoglets are usually born in June and July and start foraging at three to four weeks old.
When to mowTHE ADVICE
Researchers advise running robot mowers only in daylight and checking the lawn for hedgehogs, and other wildlife such as leverets, amphibians or baby birds, before starting.
Mow more safely03WHEN TO MOW
Hedgehogs are mostly out at night, but not always. The bar shows how likely a hedgehog is to be on the lawn, based on what hedgehog researchers and Hedgehog Street say about their habits.
Based on Rasmussen et al. (2021), Sophie Lund Rasmussen's ScienceNordic article and Hedgehog Street's pages on hoglets and robotic mower tests.
04TWO NUMBERS WORTH KNOWING
One number from the crash tests,
one from population surveys.
18 of 18
Mower models that had to touch a hedgehog to detect it
Each model was tested 12 times, with hedgehogs of four weight classes in three positions. Some models consistently caused no damage; others caused extensive damage.
CRASH TESTS · ANIMALS 2021
879,000
Hedgehogs in England, Scotland and Wales
About a quarter live in urban areas. Over half of hedgehogs have been lost from the countryside since 2000, and they have disappeared from a third of sites in towns and cities.
HEDGEHOG STREET · 2018 ESTIMATE
A later study of 19 models also found every mower had to touch the hedgehog, and that larger hedgehogs were less likely to be injured. It found very little evidence that technical features changed the risk.
05IF YOU HAVE A ROBOT MOWER
These come from the researchers' recommendations and Hedgehog Street's guidance for gardens with robot mowers.
Schedule the mower for daylight hours only, never dusk or overnight, when hedgehogs are most active.
Check for hedgehogs, and for leverets, amphibians or baby birds, before turning the mower on.
Hoglets under 200 g were not detected by any mower tested. June and July, when most are born, deserve extra care.
Researchers have designed a hedgehog crash-test dummy and propose that only mowers scoring 0–2 on their damage scale be labelled hedgehog-safe.
06BUILDING A SAFETY TEST
After testing 19 models, the researchers designed a standard test using two sizes of 3D-printed hedgehog dummy, one like a juvenile and one like an adult. They want it open-access so manufacturers can print it.
Hedgehog Street reports that the European Garden Machinery Federation, which represents robot mower makers, would soon bring in a hedgehog safety test. A label could help buyers choose hedgehog-friendly machines.
07Questions
Some do and some don't. In crash tests every model had to touch the hedgehog to detect it; some then turned away harmlessly, while others ran over it and caused serious damage.
No. The tests used hedgehogs that had died, mainly of infections, at hedgehog rehabilitation centres. Researchers have since designed 3D-printed crash-test dummies.
Researchers advise against it. Hedgehogs are nocturnal, so the recommendation is to run robot mowers only in daylight and check the lawn first.
In the 2021 tests, no mower detected dependent juvenile hedgehogs under 200 g. Larger hedgehogs were less likely to be injured in the later study.
A 2018 estimate put the number in England, Scotland and Wales at 879,000. Over half have been lost from the countryside since 2000.
08Sources
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