The UK’s adder population has fallen sharply in recent decades. Surveys indicate 90% of monitored populations are shrinking, with many groups counting fewer than ten individual snakes.
To address this, two tunnels designed to help adders cross safely were installed under Old Thornford Road, between Greenham Common and Crookham Common. The road had split two previously connected snake groups, increasing the risk of genetic isolation and local extinction.
How the tunnels work
Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust (BBOWT) secured £113,000 from Natural England’s Species Recovery Programme in 2023 to fund the installation of two 10-metre-long reptile tunnels. ACO Water Management supplied the tunnels and wing walls, which guide snakes toward the entrances.
The tunnel design admits sunlight, fresh air and moisture, essential for cold-blooded reptiles. Removable grates allow for inspection and maintenance. Installed in 2024, the tunnels were lined with gravel and include predator refuge points. Vegetation was cleared around tunnel entrances to create basking spots, and habitat piles made from local logs and brash provide extra shelter.
Fitting into UK conservation efforts
Adders are a protected species under UK law and contribute to biodiversity by maintaining balanced heathland habitats. Their decline signals broader environmental issues.
Old Thornford Road posed a barrier to adder movement. Radio tracking between 2015 and 2022 showed separate populations on each side, exposing them to risks associated with genetic isolation, including disease and mutations.
Early signs of success
In autumn 2024, BBOWT tagged five adders with radio transmitters. Although minimal movement was expected with seasonal changes, the snakes remained close to tunnel entrances. Camera traps observed various wildlife, including rodents, birds and grass snakes using the tunnels.
In April 2025, footage captured an adder crossing through a tunnel from Crookham to Greenham Common, confirming the snakes were using the new passages to safely navigate below the road.
Long-term monitoring is required to evaluate impact, but early evidence suggests the tunnels improve connectivity between populations and support biodiversity.
What it changes for conservation
Terry Wilkinson, Specialist Design & Application Engineer at ACO, said: “We expect the tunnels to last many years and hope they help the adder population return to healthier numbers by enabling safer movement.”
Debbie Lewis, Head of Ecology for BBOWT, said: “The adder tunnels reconnect isolated populations, increasing their resilience. The ACO tunnels were robust and straightforward to install, making them ideal for this project.”
Projects like this reveal practical approaches to safeguarding vulnerable species affected by UK roads and infrastructure.
For more on wildlife and biodiversity solutions, visit ACO.co.uk.
