A study conducted by Patty Briggs in East Anglia showed that 82% of the old barns with suitable features had evidence of use by bats; of these 37.5% had eveidence of the rare Natterer's bat. Many bats may be affected by timber treatment chemicals, accidentally entombed in the timbers or are driven out. Involvement of a bat specialist in the design of barn conversion at an early stage can prevent the loss of these important roosting sites.HBRC together with the Bat Group are in the process of surveying all listed barns in Hertfordshire for the presence of bats.
A Species Action Plan for the Natterer's bat Myotis nattereri has been included in the Local Biodiversity Action Plan for Hertfordshire. The recent growth in the number of barn conversions in Hertfordshire is posing a threat to many bat species including the Natterer's bat which is known to favour timber-framed barns more than 100 years old. A specific target in the Hertfordshire's Natterer's Bat Action Plan is to survey all listed barns in the county for the presence of bats by the year 2000.During the Summer of 1998, 125 Listed Barns were surveyed. Most were in East Hertfordshire (92 barns) with 27 barns in North Hertfordshire and 6 in the District of Welwyn and Hatfield.
The features of the barns were recorded along with details of bat signs and (if possible) determination of species. The habitat surrounding the barn was also documented to identify key landscape features of importance to the bats.
Of the barns visited, 74 showed evidence of use by bats; this represents 59% of the barns surveyed. Most of the barns (55 barns) had evidence for use by one species of bat with the remainder being used by two species (14 barns) or even three species (5 barns). Analysis of the barn features showed that the majority of barns (42 barns) without bats also had no obvious suitable roosting areas. This demonstrated that 89% of the barns with suitable roosting features supported bats.
The commonest species encountered was the Pipistrelle bat Pipistrellus pipistrellus which was found in 65 barns (88% of the barns used by bats). The second most common species was the Brown Long-eared bat Plecotus auritus which was roosting in 29 barns (39% of the barns used by bats). Natterer's bats Myotis nattereri were positively identified as roosting in 5 barns ( 7% of the barns used by bats). Droppings found in 6 barns could not be positively identified to species. Follow-up evening visits will be carried out to confirm the species (where not positively identified) and gain further information to establish the importance of the roosts and surrounding habitat.
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