The largest brown long-eared bat maternity roost monitored anywhere in the country for the National Bat Monitoring Programme is located in the Ecclesbourne Valley in mid-Derbyshire. The average brown long-eared bat count for the site is 199 with a maximum of 252 in 2018. The roost is only counted for the NBMP during the month of June. The roost is also home to a small number of individual common pipistrelle bats and since 2018 we have also been aware of a few Natterer’s bats, up to eight, emerging with the brown long-eared bats in June which are differentiated from the brown long-eareds through each surveyor using a second detector tuned to 90kHz. Confidence in identification of the two species is high as the site location lends itself to being able to see the ears of the long-eareds particularly well against the sky. As a service to the roost owner, in return for kindly allowing us access to undertake the annual NBMP counts, we clean out the droppings from the attic each year in February. During the annual clean in 2024 we took the opportunity to install a trailcam in the roost space. Set to timelapse mode, it was programmed to take a photograph using 940nm infrared light at 10am each day. Focused on the ridge beam above one of the four main concentrations of droppings, we hoped that this would give some idea of when the bats arrived and left, how the numbers built and provide a nice timelapse video of the roost. The results were not what we expected. The photographs show a tight huddle of at least 45 Natterer’s bats during mid-May. These disappeared from the field of view of the camera on 25th May. They may of course have moved to a different area of the roof space but we know that on the date of the 2024 NBMP count, 20thJune, only six Natterer’s bats left the roost on a perfect night when 184 brown long-eared bats went out to forage. So it seems that in addition to the large brown long-eared bat maternity colony, we have a pre-maternity roost of Natterer’s bats sharing the roof space with them. Brown long-eared bats appeared on the trailcam photographs in mid-July, and some Natterer’s bats also re-appeared. You can see the two minute timelapse video here . It was clear from the accumulations of droppings during the February 2025 roost cleaning exercise that the main brown long-eared bat roost areas were at the other end of the attic space in 2024, out of view of the single camera we installed. We hope to extend the project next year and have four cameras covering all the principal areas of the ridge beam. The results should be fascinating. To learn more about the roost see Derbyshire Bat Group Newsletter number 80 (November 2017) in the Members’ Area of this website.
Steve & Alan Roe
