Dormice typically hibernate between October and May, but they can arouse roughly every 10 days to defecate/urinate.

During winter hibernation dormice use tightly woven (often from honeysuckle), elliptical nests which are roughly the size of the tennis ball. As dormice prefer damp conditions for hibernation, these nests will usually be found beneath leaf litter, moss, logs or within hedges. Therefore, above ground clearance works are likely to disturb hibernating dormice and there is a risk of destroying any nests present.

  • If the work site is more likely to support dormice, because it falls within the known range, there are local dormice records or because of the habitat (dense scrub, hedgerows or broadleaf woodland), a pre-works survey should be conducted.
  • A useful survey method over winter is to search for gnawed hazelnuts if hazel is present on site. Dormice leave a distinctive smooth rim to these nuts unlike wood mice or bank voles. An ecologist may be necessary to confirm that these nuts have been chewed by dormice, or to perform a more extensive nest survey.
  • If evidence of dormice is found as a result of these surveys, a mitigation licence will be required from Natural England before works can proceed. 
  • Low population numbers makes it difficult to ever rule out the presence of dormice on site, so operatives should always be aware of the potential for dormice to be found during works.