At Greenham and Crookham Commons in West Berkshire we are lucky to have one of the best populations of adders in the county. These beautiful snakes are often maligned, being the UK’s only venomous snake. This could not be further from the truth as, despite being venomous, these snakes are shy and very sensitive to disturbance. They would always prefer to get away rather than attack.

Sadly, they really are in trouble with populations in decline across the UK. “Make the Adder Count”, a report collating surveys from many sites concluded that without immediate help, adders could be restricted to only a handful of sites in just 10 years’ time, with all other sites highly vulnerable to local extinction.

One of the main threats to adders is population fragmentation where groups can no longer mix and breed together. This causes issues with inbreeding and a reduced ability to adapt to sudden changes on site. Small populations can easily be wiped out with no way of numbers recovering as snakes can’t move in from elsewhere.

Through radio-tracking of adders in past years on Greenham and Crookham Commons, we have seen there are some small groups of snakes on parts of the common which are not mixing together.

Radio tracking involves sticking a small radio transmitter to the side of an adder with clear, medical adhesive tape. The weight and size are negligible and do not affect the snake’s ability to move, feed or mate. Using a receiver, we can find the signal every two-three days and record the snake’s location.

With this information we can build up a map of where snakes are moving across the common and crucially, where they are not. Barriers to the groups mixing could be very open short grassland, roads or even wide gravel paths. A snake’s willingness to cross these open areas will vary depending on time of year and the snake’s immediate needs.

Adders are most active in spring when males are exploring their local area looking for a mate, then again in summer when the snakes move from their breeding areas to the best local feeding spots. Here, their prey will include small mammals like voles or mice and amphibians like frogs and newts. An adult adder would typically eat 5-10 prey items in a typical year. Lastly, they move back to their favoured hibernation site in autumn. Adult adders, especially males can range 1-2km over a season moving between these different locations.

It is when adders are moving between sites during these periods when they may be forced to cross unfavourable areas and are at their most vulnerable. Adders are secretive animals and don’t like to be out in the open. This leaves them exposed to predators such as birds of prey, corvids, pheasants or larger mammals like foxes and stoats.

An adder is an ectotherm (cold-blooded) so need the sun’s heat for energy, but also loves to be next to scrubby cover like heather or bramble for protection. An adder’s preference is to be on the edges. The transition between the open space for sunlight and cover for protection.

BBOWT’s  radio tracking surveys showed that the Old Thornford Road at Crookham was a very clear barrier between two groups of adders. They were moving all through the heath and scrub either side of the road but never crossing it. A road poses double-danger to a snake. They are very exposed to predators while crossing and could easily be run over.

Knowing all this about adder behaviour and the distribution on the Commons, the Species Recovery Fund from Natural England presented an excellent opportunity to try something new and exciting to help them at Greenham and Crookham Commons.

So, the Adder Connections project was born. Unique in the UK, but modelled on successful projects in Canada and Spain, contractors installed two tunnels under Old Thornford Road in spring 2024 for adders and other wildlife to cross in safety.

Each tunnel is 0.5m x 0.5m in cross section and 10m long. The tunnel roof is an open grille which allows sunlight into the tunnel, warming the space to make it more inviting to cold-blooded reptiles. The base is lined with gravel providing a well-drained surface for snakes or other wildlife to cross.

Outside the tunnels is 100m of permanent reptile fencing on each side of the road, leading and funnelling the snakes to the tunnel entrances where hopefully their natural curiosity will lead them in and across the road to meet their long-lost cousins.

In addition, habitat work is being carried out to guide the snakes through favourable habitat to the tunnels. Snaking corridors (excuse the pun!) of open habitat with scrubby edges now wind through the site linking up the very best adder habitat with the tunnel entrances.

To monitor the success of the tunnels a trail camera has been secured inside each. This will record video of any movement in the tunnel. Initially, no reptiles were recorded but lots of small mammals including voles, mice and shrews went through. This is good news as they will be leaving little scent trails and are all on the menu for a hungry adder. But recently, we were delighted to spot a grass snake in a tunnel. An excellent sign that adders could soon be using them too.

Further radio tracking of adder movements in this area will be carried out in the autumn as the snakes make their way back to their hibernation sites. This will be another opportunity to detect any use of the tunnels.

In time, we hope to be able to demonstrate the success of these tunnels resulting in a healthier, more connected adder population locally. Other reserve managers will then be able to use this project as a case study to install similar structures and give these wonderful reptiles a fighting chance.

Roger Stace, Senior Land Manager (Berkshire)