There are eighteen species of bat found in the UK, although the further north you travel, the range of species declines.
In the Scottish Borders there are at least six species : common and soprano pipistrelle, Daubenton’s bat, Natterer’s bat, brown long-eared bat and, the largest species, the noctule. Two other species have also been recorded. Some of these species may hibernate in the cool damp recesses of ruined buildings.
The 16th century ruin of Cardrona Tower, located in the Tweed Valley Forest Park, has been monitored for over twenty years for the presence of bats by a team of Bat Conservation Trust volunteers and Forestry Commission Scotland rangers.
The work began when the potential for bat colonies within the vaulted roof of the cellar was realised by local bat experts. This significant long-term bat survey has recently been joined by a detailed archaeological laser scan and historic building survey. Both surveys help to enhance our understanding of the important natural and historic features present at Cardrona.
Cardrona Tower is relatively undisturbed, being little visited by humans. Access to the tower is controlled by a locked metal yett (gate). The cellar space allows for a stable cool damp climate – vital for the bats in order to remain in their torpid state. The damp affords them some condensation to drink from and ensures their survival.
In the wintertime, the bat volunteer team come to carry out two survey counts, each separated by a month. The bat workers are licensed by Scottish Natural Heritage and are well trained in bat identification. The bats are searched for using torches, to seek out their presence in amongst the crevices and, once located, are identified and counted. Any signs of damage to the bats or to the structure are also noted and a temperature reading is taken, both inside and outside the building.
Cardrona Tower doesn’t have many bats found in it each year, but does host the species expected in this area. The next nearest suitable hibernation site, or hibernaculum, is in a similar tower house located about eight miles away.
The tower was once a desirable residence with fine views down the Tweed valley. Although now ruined, it is good to know that it is still providing comfort and shelter to some important occupants…
You can find out more about Bats in the Scottish Natural Heritage leaflet Bats and People. See also http://www.snh.gov.uk/about-scotlands-nature/wildlife-and-you/bats/
With sincere thanks to Matt Ritchie (Forest Enterprise Scotland) and Laurie Campbell (bat images – pipistrelle in flight and soprano pipistrelle on wall)