Bat Hibernaculum

Second World War pillboxes have been converted in a number of locations into winter quarters for hibernating bats – a hibernacula - and in 2012 Ely Wildspace suggested to East Cambridgeshire District Council (ECDC) that the pillbox on the west side of Ely Common might be similarly converted. Nearby woodland, meadows, the open water of Roswell Pits, and the River Great Ouse all provide excellent habitat for bats, and the Common provides a corridor for bat movement. Surveys have confirmed the presence of Daubenton's bats (Myotis daubentonii), common pipistrelle (Pipistrellus pipistrellus) soprano pipistrelle (Pipistrellus pygmaeus), Brown long-eared bats (Plecotus auritus) and Noctule bats (Nyctalus noctula) around Roswell Pits, and serotine bats are suspected of being present.

Advice was given by the Cambridgeshire Bat Group on what could be done to encourage bats to use a pill box for hibernation. Firstly the pill box was secured by the addition of a robust door to prevent access by unauthorised persons. We were fortunate in having two volunteers at steel fabricators W.A. Cooke in Kiln Lane who made up a lockable steel door and fitted it in the pillbox entrance, following a clean-up operation by ECDC .

brown long-eared bat

To reduce air flow and maintain a more constant temperature internally the rear openings and one of the five firing ports were partly bricked up and the remainder bricked up completely by our volunteers. To judge the effectiveness of the closing-up of the pillbox, temperature and humidity data-loggers were placed in the interior and exterior over the winter of 2014 -2015. Whilst outside temperatures varied from -2C to 14C the internal temperatures remained in the range 2C to 10C. Relative humidity externally varied from 60% to 100%, but internally from 80% to 100%. These results showed that the extremes of temperature and low humidity were eliminated, making the conditions inside the pillbox eminently suitable for bat hibernation.

Finally, hibernation features were created inside the pillbox. Volunteers stacked bricks on the firing port ledges to provide numerous vertical gaps; bricks with frogs (hollows) were modified to form openings and the bricks suspended on back boards; and a number of wooden structures were fabricated to create both vertical and horizontal crevices of types that bats are known to utilise. The modified pillbox with its internal additions became the perfect place for bats to spend the winter.

The bats however stayed away until December 2017, when a brown long-eared bat occupied a niche in the brickwork and became the first bat to occupy the roost.

We have shown that with co-operation between stakeholders and willing volunteers, a worthwhile facility for wildlife may be created without huge effort and great expense, just perseverance and patience.

Bat boxes

In October 2015 we constructed six bat boxes. These were installed on the Ely Wildspace land at the bottom end of the boating lake. Of the six boxes that were made, five are still in place. The sixth one was damaged by squirrels or maybe a woodpecker, but has been litterally destroyed. Until now we have been unable to check these boxes as a livcence is required. It is hoped that Cambridge Bat Group will come and check the boxes for us. It is hopefuly that we will have bats using these boxes are there are a number of bird boxes we have installed and some of them have evidence of bats having been in them (guan: bat poo, in the bottom)

Want to learn more?

Click on the links below to find out more about Ely's wild spaces and how to get involved.

Get Involved: We are running events all through the year.
Using Heritage Lottery funding: memories of Ely Pits and Meadows.