One of Britain’s largest barbastelle bat populations found near St Paul’s Walden just outside Stevenage.

The colony of a minimum of 90 bats was found as part of the Hertfordshire Barbastelle Project - a research collaboration between Herts and Middlesex Bat Group and Herts and Middlesex Wildlife Trust. The project aims to learn more about the barbastelle bat which is one of the rarest bat species in the UK. The maternity colony near Stevenage is only the third to be discovered in Hertfordshire.

Tracking is done using specialist equipment to find maternity roosts. The team uses remote detectors to find a concentration of barbastelle activity and commuting routes. Nets are then set up to catch the bats which are fitted with radio tags that lead the researchers to the maternity roost where emerging bats can be counted and surveyed.

Matt Dodds is Planning & Biodiversity Manager at the Trust and one of the leads of the project. “This is a nationally important discovery – not only the existence of the population, but its sheer size is extraordinary”, he says. To put this number into perspective, Paston Great Barn Nature Reserve in Norfolk is a Special Area of Conservation (SAC), a National Nature Reserve (NNR) and a Site of Special Scientific Interest (SSSI) for its barbastelle population and is home to only 40-50 individuals.

Dr Chantal Helm is the Chair of the Herts and Middlesex Bat Group and co-leads on this project. “Thanks to our collaboration with the Trust and with the support of all the Bat Group members who contributed to the surveys, this discovery of a nationally important Barbastelle maternity colony will allow us to better understand the distribution and abundance of this rare species in Hertfordshire and help us to target monitoring and conservation efforts appropriately.”

Fergus Bowes-Lyon who owns the land the bats were found on says: "We are thrilled to discover this amazing maternity roost for barbastelle bats. This shows the benefits of the conservation approach across Easthall Farm and the woodland. We are looking forward to continuing with this work with Natural England funding. We believe that these environmental schemes, including grassland, hedges and field margins on the surrounding farm land, have made a significant role in creating a supportive habitat for these bats."

Now in its fourth year, and having already found two maternity colonies, the project aims to find out more about the distribution of barbastelle bats in the county and to get insights into the behaviour of this rare species. These findings can then be used to work with landowners to identify suitable roost sites and hopefully find more colonies. If you believe that your land comprises the features barbastelles need – old oak trees with splits, cracks and peeling bark in ancient woodland – please make sure to get advice before doing any tree removal work.