Est. Reading: 2 minutes

The recent chilly Siberian conditions meant that those creatures that hibernate would have been well and truly hunkered down and tucked up. In our considerably more open winters animals tend to break their hibernation during mild spells.

Bats in particular were once thought to hibernate all winter but recording and research has shown this is not the case. They will move between sites as weather conditions dictate. Indeed, on occasion the odd bat can be seen flying during very mild spells. On 21st December a Noctule, our largest species of bat, was mobbed by gulls while flying during the day over North Meadow Common. By and large, however, bats are much less active during the winter because their food resource is scarce and hunting for insects in cold weather expends more energy than can be replaced.

In the early 1990s the Sudbury Common Lands Charity converted the King’s Marsh World War Two pillbox into a bat hibernacula. Bulmer brickworks produced special ‘bat bricks’ with bat-sized cavities in them and these were fixed to the roof. A door is required to prevent entry and disturbance throughout the year. Indeed, most people would have been shocked at the unimaginable quantity of accumulated rubbish in every pillbox. Now, with access denied to human mammals, they provide pristine accommodation for our only flying mammals as well as for over-wintering butterflies.

The King’s Marsh conversion was followed by funding and conversion work by the Dedham Vale and Stour Valley Countryside Project for further pillboxes in the valley including four on the Sudbury riverside plus a more secure steel door for the King’s Marsh box. The Sudbury boxes attracted wintering bats almost immediately, albeit in very low numbers, while those elsewhere are only just beginning to attract residents.

Each winter all ten boxes are surveyed for hibernating bats. Surveyors are qualified specialists who hold licences to carry out this work. This winter the count recorded twenty four bats, only two of which were found in boxes outside Sudbury. This count was down from thirty two for last year but weather conditions affect where bats roost and hibernate. It is also possible that the accommodation may not entirely suitable for bats as temperatures inside can fluctuate. There is certainly more to be learned about their requirements.

During February hibernating species included Natterer’s, brown long-eared and Daubenton’s and these records contribute to the bigger picture. Gemma Holmes of the Suffolk Bat Group took a superb photograph of a brown long-eared bat tucked up in a drilled-out breeze block in one of the Sudbury pillboxes. As time passes, more bats are taking residence in these ‘desirable developments’ during the winter so these defences untested by war are serving a very useful purpose seventy five years on after their construction.




The Christopher Centre
10 Gainsborough Street
CO10 2EU
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