TWO-MILE BOTTOM BAT HIBERNACULUM
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TWO MILE BOTTOM BAT HIBERNACULUM FROM FOLLY TO FANTASY NICK GIBBONS Introduction At some time in 2002 John Goldsmith suggested to me the idea of a new artificial bat hibernaculum for the Thetford Forest, a pipe-dream he had harboured for several years and, in a weak moment, I appear to have agreed with him. The site he had in mind, having considered most of the forest area, was at Two Mile Bottom where a small, shallow valley, possibly a site of old sand-diggings, ran down almost to the River Ouse. The bottom of the shallow valley had no trees and those at the top of the slopes were relatively immature at 22 years of age. It fulfilled several key requirements: near a river; existing bat usage along the water-course that had been confirmed by detectors; a north-facing entrance; shaded; away from existing used tracks and away from areas of high human usage; no archaeological sites present to disturb, while the existing valley shape meant much less soil to move, so a less expensive project. A plan for a 100 metre-long ‘Y’ shaped tunnel was put together by John Goldsmith and myself based on a similar construction to the very successful High Lodge hibernaculum that had been built in 1991 to a ‘Goldsmith/Tilford’ design although the general design and approach had been used at several sites. The High Lodge hibernaculum had a wide variety of hibernating bat species, including Barbastelle, At that point it was not thought that the new tunnel would be too expensive and the three quotes received for the work were a bit of a shock at over £40,000. With money from Forestry Commission and a grant from WREN supported by Forest Heath District Council it was decided that it would be possible to build a smaller, ‘Y’ shaped tunnel at around £20000, with provision to extend it at a later date if funds became available. In the autumn of 2003 the Friends of Thetford Forest (FoTF) volunteer group carried out clearance of obstructing scrub, and all was set to go. At the last minute additional funding became available from the Environment Agency, and Suffolk County Council also sponsored the interpretation and access facilities, thus allowing the tunnel to be built to the planned and full size.
Construction Although FC is technically exempt from the requirement to apply for planning permission from the local authority there is agreement that normal planning requirements are followed. A hibernaculum is something of a moot point as it does not neatly fit into any category such as a dwelling, agricultural building etc. Having got planning permission construction commenced in February 2004. The hibernaculum was built by a cut and back-fill process to produce a Y shaped tunnel some 95m long. The walls are concrete blocks whilst the ceiling was designed to be of floated reinforced concrete with bat bricks set into the ceiling. Due to its length manholes were fitted at the end of each arm
Trans. Suffolk Nat. Soc. 49 (2013)